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Dateianzeige für spax (3.4.0)
usr/share/doc/spax/spax.txtSPAX(1L) Schily´s USER COMMANDS SPAX(1L)
NAME
pax - portable archive interchange
SYNOPSIS
spax [other options] [-cdnv] [-H|-L] [-f archive] [-o options]...
[-s replstr]... [pattern...]
spax -r [other options] [-cdiknuv] [-H|-L] [-f archive] [-o options]...
[-p string]... [-s replstr]... [pattern...]
spax -w [other options] [-dituvX] [-H|-L] [-b blocksize] [-a] [-f ar-
chive] [-o options]... [-s replstr]... [-x format] [file...]
spax -r -w[other options] [-diklntuvX] [-H|-L] [-o options]...
[-p string]... [-s replstr]... [file...] directory
DESCRIPTION
The pax utility shall read, write, and write lists of the members of ar-
chive files and copy directory hierarchies. A variety of archive formats
shall be supported; see the -x format option.
The action to be taken depends on the presence of the -r and -w options.
The four combinations of -r and -w are referred to as the four modes of
operation: list, read, write, and copy modes, corresponding respectively to
the four forms shown in the SYNOPSIS section.
list In list mode (when neither -r nor -w are specified), pax shall write
the names of the members of the archive file read from the standard
input, with pathnames matching the specified patterns, to standard
output. If a named file is of type directory, the file hierarchy
rooted at that file shall be listed as well.
read In read mode (when -r is specified, but -w is not), pax shall
extract the members of the archive file read from the standard
input, with pathnames matching the specified patterns. If an
extracted file is of type directory, the file hierarchy rooted at
that file shall be extracted as well. The extracted files shall be
created performing pathname resolution with the directory in which
pax was invoked as the current working directory.
If an attempt is made to extract a directory when the directory
already exists, this shall not be considered an error. If an attempt
is made to extract a FIFO when the FIFO already exists, this shall
not be considered an error.
The ownership, access, and modification times, and file mode of the
restored files are discussed under the -p option.
write In write mode (when -w is specified, but -r is not), pax shall write
the contents of the file operands to the standard output in an ar-
chive format. If no file operands are specified, a list of files to
copy, one per line, shall be read from the standard input. A file of
type directory shall include all of the files in the file hierarchy
rooted at the file.
copy In copy mode (when both -r and -w are specified), pax shall copy the
file operands to the destination directory.
If no file operands are specified, a list of files to copy, one per
line, shall be read from the standard input. A file of type direc-
tory shall include all of the files in the file hierarchy rooted at
the file.
The effect of the copy shall be as if the copied files were written
to an archive file and then subsequently extracted, except that
there may be hard links between the original and the copied files.
If the destination directory is a subdirectory of one of the files
to be copied, the results are unspecified. If the destination direc-
tory is a file of a type not defined by the System Interfaces volume
of IEEE Std 1003.1-2001, the results are implementation-defined;
otherwise, it shall be an error for the file named by the directory
operand not to exist, not be writable by the user, or not be a file
of type directory.
In read or copy modes, if intermediate directories are necessary to extract
an archive member, pax shall perform actions equivalent to the mkdir()
function defined in the System Interfaces volume of IEEE Std 1003.1-2001,
called with the following arguments:
· The intermediate directory used as the path argument.
· The value of the bitwise-inclusive OR of S_IRWXU, S_IRWXG, and
S_IRWXO as the mode argument.
If any specified pattern or file operands are not matched by at least one
file or archive member, pax shall write a diagnostic message to standard
error for each one that did not match and exit with a non-zero exit status.
The archive formats described in the EXTENDED DESCRIPTION section shall be
automatically detected on input. The default output archive format shall be
implementation-defined.
The spax implementation defaults to -x ustar.
A single archive can span multiple files. The pax utility shall determine,
in an implementation-defined manner, what file to read or write as the next
file.
If the selected archive format supports the specification of linked files,
it shall be an error if these files cannot be linked when the archive is
extracted, except that if the files to be linked are symbolic links and the
system is not capable of making hard links to symbolic links, then separate
copies of the symbolic link shall be created instead. For archive formats
that do not store file contents with each name that causes a hard link, if
the file that contains the data is not extracted during this pax session,
either the data shall be restored from the original file, or a diagnostic
message shall be displayed with the name of a file that can be used to
extract the data. In traversing directories, pax shall detect infinite
loops; that is, entering a previously visited directory that is an ancestor
of the last file visited. When it detects an infinite loop, pax shall
write a diagnostic message to standard error and shall terminate.
OPTIONS
The pax utility shall conform to the Base Definitions volume of IEEE Std
1003.1-2001, Section 12.2, Utility Syntax Guidelines, except that the order
of presentation of the -o, -p, and -s options is significant. See also the
OTHER OPTIONS section.
The following options shall be supported:
-r Read an archive file from standard input.
-w Write files to the standard output in the specified archive format.
-a Append files to the end of the archive. It is implementation-defined
which devices on the system support appending. Additional file for-
mats unspecified by this volume of IEEE Std 1003.1-2001 may impose
restrictions on appending.
-b blocksize
Block the output at a positive decimal integer number of bytes per
write to the archive file. Devices and archive formats may impose
restrictions on blocking. Blocking shall be automatically determined
on input. Conforming applications shall not specify a blocksize
value larger than 32256. Default blocking when creating archives
depends on the archive format. (See the -x option below.)
-c Match all file or archive members except those specified by the pat-
tern or file operands.
-d Cause files of type directory being copied or archived or archive
members of type directory being extracted or listed to match only
the file or archive member itself and not the file hierarchy rooted
at the file.
-f archive
Specify the pathname of the input or output archive, overriding the
default standard input (in list or read modes) or standard output
(write mode).
-H If a symbolic link referencing a file of type directory is specified
on the command line, pax shall archive the file hierarchy rooted in
the file referenced by the link, using the name of the link as the
root of the file hierarchy. Otherwise, if a symbolic link referenc-
ing a file of any other file type which pax can normally archive is
specified on the command line, then pax shall archive the file ref-
erenced by the link, using the name of the link. The default behav-
ior shall be to archive the symbolic link itself.
-i Interactively rename files or archive members. For each archive mem-
ber matching a pattern operand or file matching a file operand, a
prompt shall be written to the file /dev/tty. The prompt shall con-
tain the name of the file or archive member, but the format is oth-
erwise unspecified. A line shall then be read from /dev/tty. If this
line is blank, the file or archive member shall be skipped. If this
line consists of a single period, the file or archive member shall
be processed with no modification to its name. Otherwise, its name
shall be replaced with the contents of the line. The pax utility
shall immediately exit with a non-zero exit status if end-of-file is
encountered when reading a response or if /dev/tty cannot be opened
for reading and writing.
The results of extracting a hard link to a file that has been
renamed during extraction are unspecified.
-k Prevent the overwriting of existing files.
-l (The letter ell.) In copy mode, hard links shall be made between the
source and destination file hierarchies whenever possible. If speci-
fied in conjunction with -H or -L, when a symbolic link is encoun-
tered, the hard link created in the destination file hierarchy shall
be to the file referenced by the symbolic link. If specified when
neither -H nor -L is specified, when a symbolic link is encountered,
the implementation shall create a hard link to the symbolic link in
the source file hierarchy or copy the symbolic link to the destina-
tion.
-L If a symbolic link referencing a file of type directory is specified
on the command line or encountered during the traversal of a file
hierarchy, pax shall archive the file hierarchy rooted in the file
referenced by the link, using the name of the link as the root of
the file hierarchy. Otherwise, if a symbolic link referencing a
file of any other file type which pax can normally archive is speci-
fied on the command line or encountered during the traversal of a
file hierarchy, pax shall archive the file referenced by the link,
using the name of the link. The default behavior shall be to archive
the symbolic link itself.
-n Select the first archive member that matches each pattern operand.
No more than one archive member shall be matched for each pattern
(although members of type directory shall still match the file hier-
archy rooted at that file).
-o options
Provide information to the implementation to modify the algorithm
for extracting or writing files. The value of options shall consist
of one or more comma-separated keywords of the form:
keyword[[:]=value][,keyword[[:]=value],...]
Some keywords apply only to certain file formats, as indicated with
each description. Use of keywords that are inapplicable to the file
format being processed produces undefined results.
Keywords in the options argument shall be a string that would be a
valid portable filename as described in the Base Definitions volume
of IEEE Std 1003.1-2001, Section 3.276, Portable Filename Character
Set.
Note: Keywords are not expected to be filenames, merely to follow
the same character composition rules as portable filenames.
Keywords can be preceded with white space. The value field shall
consist of zero or more characters; within value, the application
shall precede any literal comma with a backslash, which shall be
ignored, but preserves the comma as part of value. A comma as the
final character, or a comma followed solely by white space as the
final characters, in options shall be ignored. Multiple -o options
can be specified; if keywords given to these multiple -o options
conflict, the keywords and values appearing later in command line
sequence shall take precedence and the earlier shall be silently
ignored. The following keyword values of options shall be supported
for the file formats as indicated:
delete=pattern
(Applicable only to the -x pax format.) When used in write or
copy mode, pax shall omit from extended header records that
it produces any keywords matching the string pattern. When
used in read or list mode, pax shall ignore any keywords
matching the string pattern in the extended header records.
In both cases, matching shall be performed using the pattern
matching notation described in Patterns Matching a Single
Character and Patterns Matching Multiple Characters. For
example:
-o delete=security.*
would suppress security-related information. See pax Extended
Header for extended header record keyword usage.
When multiple -o delete=pattern options are specified, the
patterns shall be additive; all keywords matching the speci-
fied string patterns shall be omitted from extended header
records that pax produces.
exthdr.name=string
(Applicable only to the -x pax format.) This keyword allows
user control over the name that is written into the ustar
header blocks for the extended header produced under the cir-
cumstances described in pax Header Block. The name shall be
the contents of string, after the following character substi-
tutions have been made:
┌─────────────────┬─────────────────────────────────────────────┐
│string Includes: │ Replaced By: │
├─────────────────┼─────────────────────────────────────────────┤
│%d │ The directory name of the file, equivalent │
│ │ to the result of the dirname utility on the │
│ │ translated pathname. │
├─────────────────┼─────────────────────────────────────────────┤
│%f │ The filename of the file, equivalent to the │
│ │ result of the basename utility on the │
│ │ translated pathname. │
├─────────────────┼─────────────────────────────────────────────┤
│%p │ The process ID of the pax process. │
├─────────────────┼─────────────────────────────────────────────┤
│%% │ A '%' character. │
└─────────────────┴─────────────────────────────────────────────┘
Any other '%' characters in string produce undefined results.
If no -o exthdr.name= string is specified, pax shall use the
following default value:
%d/PaxHeaders.%p/%f
globexthdr.name=string
(Applicable only to the -x pax format.) When used in write or
copy mode with the appropriate options, pax shall create
global extended header records with ustar header blocks that
will be treated as regular files by previous versions of pax.
This keyword allows user control over the name that is writ-
ten into the ustar header blocks for global extended header
records. The name shall be the contents of string, after the
following character substitutions have been made:
┌─────────────────┬─────────────────────────────────────────────┐
│string Includes: │ Replaced By: │
├─────────────────┼─────────────────────────────────────────────┤
│%n │ An integer that represents the sequence │
│ │ number of the global extended header record │
│ │ in the archive, starting at 1. │
├─────────────────┼─────────────────────────────────────────────┤
│%p │ The process ID of the pax process. │
├─────────────────┼─────────────────────────────────────────────┤
│%% │ A '%' character. │
└─────────────────┴─────────────────────────────────────────────┘
Any other '%' characters in string produce undefined results.
If no -o globexthdr.name=string is specified, pax shall use
the following default value:
$TMPDIR/GlobalHead.%p.%n
where $TMPDIR represents the value of the TMPDIR environment
variable. If TMPDIR is not set, pax shall use /tmp.
invalid=action
(Applicable only to the -x pax format.) This keyword allows
user control over the action pax takes upon encountering val-
ues in an extended header record that, in read or copy mode,
are invalid in the destination hierarchy or, in list mode,
cannot be written in the codeset and current locale of the
implementation. The following are invalid values that shall
be recognized by pax:
+ In read or copy mode, a filename or link name that
contains character encodings invalid in the destina-
tion hierarchy. (For example, the name may contain
embedded NULs.)
+ In read or copy mode, a filename or link name that is
longer than the maximum allowed in the destination
hierarchy (for either a pathname component or the
entire pathname).
+ In list mode, any character string value (filename,
link name, user name, and so on) that cannot be writ-
ten in the codeset and current locale of the implemen-
tation.
The following mutually-exclusive values of the action argu-
ment are supported:
bypass In read or copy mode, pax shall bypass the file, caus-
ing no change to the destination hierarchy. In list
mode, pax shall write all requested valid values for
the file, but its method for writing invalid values is
unspecified.
rename In read or copy mode, pax shall act as if the -i
option were in effect for each file with invalid file-
name or link name values, allowing the user to provide
a replacement name interactively. In list mode, pax
shall behave identically to the bypass action.
UTF-8 When used in read, copy, or list mode and a filename,
link name, owner name, or any other field in an
extended header record cannot be translated from the
pax UTF-8 codeset format to the codeset and current
locale of the implementation, pax shall use the actual
UTF-8 encoding for the name.
write In read or copy mode, pax shall write the file, trans-
lating the name, regardless of whether this may over-
write an existing file with a valid name. In list
mode, pax shall behave identically to the bypass
action.
If no -o invalid=option is specified, pax shall act as if -o
invalid= bypass were specified. Any overwriting of existing
files that may be allowed by the -o invalid= actions shall be
subject to permission(-p) and modification time (-u) restric-
tions, and shall be suppressed if the -k option is also spec-
ified.
linkdata
(Applicable only to the -x pax format.) In write mode, pax
shall write the contents of a file to the archive even when
that file is merely a hard link to a file whose contents have
already been written to the archive.
listopt=format
This keyword specifies the output format of the table of con-
tents produced when the -v option is specified in list mode.
See List Mode Format Specifications. To avoid ambiguity, the
listopt= format shall be the only or final keyword= value
pair in a -o option-argument; all characters in the remainder
of the option-argument shall be considered part of the format
string. When multiple -o listopt= format options are speci-
fied, the format strings shall be considered a single, con-
catenated string, evaluated in command line order.
times (Applicable only to the -x pax format.) When used in write or
copy mode, pax shall include atime and mtime extended header
records for each file. See pax Extended Header File Times.
In addition to these keywords, if the -x pax format is specified,
any of the keywords and values defined in pax Extended Header,
including implementation extensions, can be used in -o option-argu-
ments, in either of two modes:
keyword=value
When used in write or copy mode, these keyword/value pairs
shall be included at the beginning of the archive as typeflag
g global extended header records. When used in read or list
mode, these keyword/value pairs shall act as if they had been
at the beginning of the archive as typeflag g global extended
header records.
keyword:=value
When used in write or copy mode, these keyword/value pairs
shall be included as records at the beginning of a typeflag x
extended header for each file. (This shall be equivalent to
the equal-sign form except that it creates no typeflag g
global extended header records.) When used in read or list
mode, these keyword/value pairs shall act as if they were
included as records at the end of each extended header; thus,
they shall override any global or file-specific extended
header record keywords of the same names. For example, in the
command:
pax -r -o "gname:=mygroup," s.
Any non-null character can be used as a delimiter ( '/' shown here).
Multiple -s expressions can be specified; the expressions shall be
applied in the order specified, terminating with the first success-
ful substitution. The optional trailing 'g' is as defined in the ed
utility. The optional trailing 'p' shall cause successful substitu-
tions to be written to standard error. File or archive member names
that substitute to the empty string shall be ignored when reading
and writing archives.
-t When reading files from the file system, and if the user has the
permissions required by utime() to do so, set the access time of
each file read to the access time that it had before being read by
pax.
-u Ignore files that are older (having a less recent file modification
time) than a pre-existing file or archive member with the same name.
In read mode, an archive member with the same name as a file in the
file system shall be extracted if the archive member is newer than
the file. In write mode, an archive file member with the same name
as a file in the file system shall be superseded if the file is
newer than the archive member. If -a is also specified, this is
accomplished by appending to the archive; otherwise, it is unspeci-
fied whether this is accomplished by actual replacement in the ar-
chive or by appending to the archive. In copy mode, the file in the
destination hierarchy shall be replaced by the file in the source
hierarchy or by a link to the file in the source hierarchy if the
file in the source hierarchy is newer.
-v In list mode, produce a verbose table of contents (see the STDOUT
section). Otherwise, write archive member pathnames to standard
error (see the STDERR section).
-x format
Specify the output archive format. The pax utility shall support the
following formats:
cpio The cpio interchange format; see the EXTENDED DESCRIPTION
section. The default blocksize for this format for character
special archive files shall be 5120. Implementations shall
support all blocksize values less than or equal to 32256 that
are multiples of 512.
pax The pax interchange format; see the EXTENDED DESCRIPTION sec-
tion. The default blocksize for this format for character
special archive files shall be 5120. Implementations shall
support all blocksize values less than or equal to 32256 that
are multiples of 512.
ustar The tar interchange format; see the EXTENDED DESCRIPTION sec-
tion. The default blocksize for this format for character
special archive files shall be 10240. Implementations shall
support all blocksize values less than or equal to 32256 that
are multiples of 512.
Implementation-defined formats shall specify a default block size as
well as any other block sizes supported for character special ar-
chive files.
Any attempt to append to an archive file in a format different from
the existing archive format shall cause pax to exit immediately with
a non-zero exit status.
In copy mode, if no -x format is specified, pax shall behave as if
-x pax were specified.
-X When traversing the file hierarchy specified by a pathname, pax
shall not descend into directories that have a different device ID (
st_dev; see the System Interfaces volume of IEEE Std 1003.1-2001,
stat()).
Specifying more than one of the mutually-exclusive options -H and -L shall
not be considered an error and the last option specified shall determine
the behavior of the utility.
The options that operate on the names of files or archive members (-c, -i,
-n, -s, -u, and -v) shall interact as follows. In read mode, the archive
members shall be selected based on the user-specified pattern operands as
modified by the -c, -n, and -u options. Then, any -s and -i options shall
modify, in that order, the names of the selected files. The -v option shall
write names resulting from these modifications.
In write mode, the files shall be selected based on the user-specified
pathnames as modified by the -n and -u options. Then, any -s and -i
options shall modify, in that order, the names of these selected files. The
-v option shall write names resulting from these modifications.
If both the -u and -n options are specified, pax shall not consider a file
selected unless it is newer than the file to which it is compared.
List Mode Format Specifications
The manual page for spax is not yet ready. The following text is a quota-
tion from the POSIX.1-2001 standard.
In list mode with the -o listopt=format option, the format argument shall
be applied for each selected file. The pax utility shall append a
to the listopt output for each selected file. The format argument shall be
used as the format string described in the Base Definitions volume of IEEE
Std 1003.1-2001, Chapter 5, File Format Notation, with the exceptions 1.
through 5. defined in the EXTENDED DESCRIPTION section of printf(3), plus
the following exceptions:
6. The sequence (keyword) can occur before a format conversion speci-
fier. The conversion argument is defined by the value of keyword.
The implementation shall support the following keywords:
· Any of the Field Name entries in ustar Header Block and
Octet-Oriented cpio Archive Entry. The implementation may
support the cpio keywords without the leading c_ in addition
to the form required by Values for cpio c_mode Field.
· Any keyword defined for the extended header in pax Extended
Header.
· Any keyword provided as an implementation-defined extension
within the extended header defined in pax Extended Header.
For example, the sequence "%(charset)s" is the string value of the
name of the character set in the extended header.
The result of the keyword conversion argument shall be the value
from the applicable header field or extended header, without any
trailing NULs.
All keyword values used as conversion arguments shall be translated
from the UTF-8 encoding to the character set appropriate for the
local file system, user database, and so on, as applicable.
7. An additional conversion specifier character, T, shall be used to
specify time formats. The T conversion specifier character can be
preceded by the sequence (keyword=subformat), where subformat is a
date format as defined by date operands. The default keyword shall
be mtime and the default subformat shall be:
%b %e %H:%M %Y
8. An additional conversion specifier character, M, shall be used to
specify the file mode string as defined in ls(1) Standard Output. If
(keyword) is omitted, the mode keyword shall be used. For example,
%.1M writes the single character corresponding to the
field of the ls -l command.
9. An additional conversion specifier character, D, shall be used to
specify the device for block or special files, if applicable, in an
implementation-defined format. If not applicable, and (keyword) is
specified, then this conversion shall be equivalent to %(keyword)u.
If not applicable, and (keyword) is omitted, then this conversion
shall be equivalent to .
10. An additional conversion specifier character, F, shall be used to
specify a pathname. The F conversion character can be preceded by a
sequence of comma-separated keywords:
(keyword[,keyword] ... )
The values for all the keywords that are non-null shall be concate-
nated together, each separated by a '/'. The default shall be (path)
if the keyword path is defined; otherwise, the default shall be
(prefix, name).
11. An additional conversion specifier character, L, shall be used to
specify a symbolic line expansion. If the current file is a symbolic
link, then %L shall expand to:
"%s -> %s", ,
Otherwise, the %L conversion specification shall be the equivalent of %F.
OPERANDS
The following operands shall be supported:
directory
The destination directory pathname for copy mode.
file A pathname of a file to be copied or archived.
pattern
A pattern matching one or more pathnames of archive members. A pat-
tern must be given in the name-generating notation of the pattern
matching notation in Pattern Matching Notation , including the file-
name expansion rules in Patterns Used for Filename Expansion. The
default, if no pattern is specified, is to select all members in the
archive.
STDIN
In write mode, the standard input shall be used only if no file operands
are specified. It shall be a text file containing a list of pathnames, one
per line, without leading or trailing s.
In list and read modes, if -f is not specified, the standard input shall be
an archive file.
Otherwise, the standard input shall not be used.
INPUT FILES
The input file named by the archive option-argument, or standard input when
the archive is read from there, shall be a file formatted according to one
of the specifications in the EXTENDED DESCRIPTION section or some other
implementation-defined format.
The file /dev/tty shall be used to write prompts and read responses.
ENVIRONMENT VARIABLES
The following environment variables shall affect the execution of pax:
LANG Provide a default value for the internationalization variables that
are unset or null. (See the Base Definitions volume of IEEE Std
1003.1-2001, Section 8.2, Internationalization Variables for the
precedence of internationalization variables used to determine the
values of locale categories.)
LC_ALL If set to a non-empty string value, override the values of all the
other internationalization variables.
LC_COLLATE
Determine the locale for the behavior of ranges, equivalence
classes, and multi-character collating elements used in the pattern
matching expressions for the pattern operand, the basic regular
expression for the -s option, and the extended regular expression
defined for the yesexpr locale keyword in the LC_MESSAGES category.
LC_CTYPE
Determine the locale for the interpretation of sequences of bytes of
text data as characters (for example, single-byte as opposed to
multi-byte characters in arguments and input files), the behavior of
character classes used in the extended regular expression defined
for the yesexpr locale keyword in the LC_MESSAGES category, and pat-
tern matching.
LC_MESSAGES
Determine the locale for the processing of affirmative responses
that should be used to affect the format and contents of diagnostic
messages written to standard error.
LC_TIME
Determine the format and contents of date and time strings when the
-v option is specified.
NLSPATH
[XSI] [Option Start] Determine the location of message catalogs for
the processing of LC_MESSAGES . [Option End]
TMPDIR Determine the pathname that provides part of the default global
extended header record file, as described for the -o globexthdr=
keyword in the OPTIONS section.
TZ Determine the timezone used to calculate date and time strings when
the -v option is specified. If TZ is unset or null, an unspecified
default timezone shall be used.
ASYNCHRONOUS EVENTS
Default.
STDOUT
In write mode, if -f is not specified, the standard output shall be the ar-
chive formatted according to one of the specifications in the EXTENDED
DESCRIPTION section, or some other implementation-defined format (see -x
format).
In list mode, when the -o listopt= format has been specified, the selected
archive members shall be written to standard output using the format
described under List Mode Format Specifications. In list mode without the
-o listopt= format option, the table of contents of the selected archive
members shall be written to standard output using the following format:
"%s\n",
If the -v option is specified in list mode, the table of contents of the
selected archive members shall be written to standard output using the fol-
lowing formats.
For pathnames representing hard links to previous members of the archive:
"%s == %s\n", ,
For all other pathnames:
"%s\n",
where shall be the format specified by the ls(1) utility
with the -l option. When writing pathnames in this format, it is unspeci-
fied what is written for fields for which the underlying archive format
does not have the correct information, although the correct number of
-separated fields shall be written.
In list mode, standard output shall not be buffered more than a line at a
time.
STDERR
If -v is specified in read, write, or copy modes, pax shall write the path-
names it processes to the standard error output using the following format:
"%s\n",
These pathnames shall be written as soon as processing is begun on the file
or archive member, and shall be flushed to standard error. The trailing
, which shall not be buffered, is written when the file has been
read or written.
If the -s option is specified, and the replacement string has a trailing
'p', substitutions shall be written to standard error in the following for-
mat:
"%s >> %s\n", ,
In all operating modes of pax, optional messages of unspecified format con-
cerning the input archive format and volume number, the number of files,
blocks, volumes, and media parts as well as other diagnostic messages may
be written to standard error.
In all formats, for both standard output and standard error, it is unspeci-
fied how non-printable characters in pathnames or link names are written.
When pax is in read mode or list mode, using the -x pax archive format, and
a filename, link name, owner name, or any other field in an extended header
record cannot be translated from the pax UTF-8 codeset format to the code-
set and current locale of the implementation, pax shall write a diagnostic
message to standard error, shall process the file as described for the -o
invalid= option, and then shall process the next file in the archive.
OUTPUT FILES
In read mode, the extracted output files shall be of the archived file
type. In copy mode, the copied output files shall be the type of the file
being copied. In either mode, existing files in the destination hierarchy
shall be overwritten only when all permission (-p), modification time (-u),
and invalid-value (-o invalid=) tests allow it.
In write mode, the output file named by the -f option-argument shall be a
file formatted according to one of the specifications in the EXTENDED
DESCRIPTION section, or some other implementation-defined format.
EXTENDED DESCRIPTION
pax Interchange Format
A pax archive tape or file produced in the -x pax format shall contain a
series of blocks. The physical layout of the archive shall be identical to
the ustar format described in ustar Interchange Format. Each file archived
shall be represented by the following sequence:
· An optional header block with extended header records. This
header block is of the form described in pax Header Block,
with a typeflag value of x or g. The extended header
records, described in pax Extended Header, shall be included
as the data for this header block.
· A header block that describes the file. Any fields in the
preceding optional extended header shall override the associ-
ated fields in this header block for this file.
· Zero or more blocks that contain the contents of the file.
At the end of the archive file there shall be two 512-byte blocks filled
with binary zeros, interpreted as an end-of-archive indicator.
A schematic of an example archive with global extended header records and
two actual files is shown in pax Format Archive Example. In the example,
the second file in the archive has no extended header preceding it, presum-
ably because it has no need for extended attributes.
Figure: pax Format Archive Example
┌──────────────────────────────┬─────────────────────────────────────────────┐
│ustar Header [typeflag = 'g'] │ │
├──────────────────────────────┤ Global Extended header │
│Global Extended Header Data │ │
├──────────────────────────────┼─────────────────────────────────────────────┤
│ustar Header [typeflag = 'x'] │ │
├──────────────────────────────┤ │
│Extended Header Data │ │
├──────────────────────────────┤ File 1: Extended Header data is included │
│ustar Header [typeflag = '0'] │ │
├──────────────────────────────┤ │
│Data for File 1 │ │
├──────────────────────────────┼─────────────────────────────────────────────┤
│ustar Header [typeflag = '0'] │ │
├──────────────────────────────┤ File 2: No Extended Header data is included │
│Data for File 2 │ │
├──────────────────────────────┼─────────────────────────────────────────────┤
│Block of binary Zeroes │ │
├──────────────────────────────┤ End of Archive Indicator │
│Block of binary Zeroes │ │
└──────────────────────────────┴─────────────────────────────────────────────┘
pax Header Block
The pax header block shall be identical to the ustar header block described
in ustar Interchange Format, except that two additional typeflag values are
defined:
x Represents extended header records for the following file in the ar-
chive (which shall have its own ustar header block). The format of
these extended header records shall be as described in pax Extended
Header.
g Represents global extended header records for the following files in
the archive. The format of these extended header records shall be as
described in pax Extended Header. Each value shall affect all sub-
sequent files that do not override that value in their own extended
header record and until another global extended header record is
reached that provides another value for the same field. The typeflag
g global headers should not be used with interchange media that
could suffer partial data loss in transporting the archive.
For both of these types, the size field shall be the size of the extended
header records in octets. The other fields in the header block are not
meaningful to this version of the pax utility. However, if this archive is
read by a pax utility conforming to the ISO POSIX-2:1993 standard, the
header block fields are used to create a regular file that contains the
extended header records as data. Therefore, header block field values
should be selected to provide reasonable file access to this regular file.
A further difference from the ustar header block is that data blocks for
files of typeflag 1 (the digit one) (hard link) may be included, which
means that the size field may be greater than zero. Archives created by pax
-o linkdata shall include these data blocks with the hard links.
pax Extended Header
A pax extended header contains values that are inappropriate for the ustar
header block because of limitations in that format: fields requiring a
character encoding other than that described in the ISO/IEC 646:1991 stan-
dard, fields representing file attributes not described in the ustar
header, and fields whose format or length do not fit the requirements of
the ustar header. The values in an extended header add attributes to the
following file (or files; see the description of the typeflag g header
block) or override values in the following header block(s), as indicated in
the following list of keywords.
An extended header shall consist of one or more records, each constructed
as follows:
"%d %s=%s\n", , ,
The extended header records shall be encoded according to the ISO/IEC
10646-1:2000 standard (UTF-8). The field, , equals sign,
and shown shall be limited to the portable character set, as
encoded in UTF-8. The and fields can be any UTF-8 charac-
ters. The field shall be the decimal length of the extended header
record in octets, including the trailing .
The field shall be one of the entries from the following list or
a keyword provided as an implementation extension. Keywords consisting
entirely of lowercase letters, digits, and periods are reserved for future
standardization. A keyword shall not include an equals sign. (In the fol-
lowing list, the notations "file(s)" or "block(s)" is used to acknowledge
that a keyword affects the following single file after a typeflag x
extended header, but possibly multiple files after typeflag g. Any
requirements in the list for pax to include a record when in write or copy
mode shall apply only when such a record has not already been provided
through the use of the -o option. When used in copy mode, pax shall behave
as if an archive had been created with applicable extended header records
and then extracted.)
atime The file access time for the following file(s), equivalent to the
value of the st_atime member of the stat structure for a file, as
described by the stat(2) function. The access time shall be restored
if the process has the appropriate privilege required to do so. The
format of the shall be as described in pax Extended Header
File Times.
charset
The name of the character set used to encode the data in the follow-
ing file(s). The entries in the following table are defined to refer
to known standards; additional names may be agreed on between the
originator and recipient.
┌────────────────────────┬───────────────────────────────┐
│ │ Formal Standard │
├────────────────────────┼───────────────────────────────┤
│ISO-IR 646 1990 │ ISO/IEC 646:1990 │
│ISO-IR 8859 1 1998 │ ISO/IEC 8859-1:1998 │
│ISO-IR 8859 2 1999 │ ISO/IEC 8859-2:1999 │
│ISO-IR 8859 3 1999 │ ISO/IEC 8859-3:1999 │
│ISO-IR 8859 4 1998 │ ISO/IEC 8859-4:1998 │
│ISO-IR 8859 5 1999 │ ISO/IEC 8859-5:1999 │
│ISO-IR 8859 6 1999 │ ISO/IEC 8859-6:1999 │
│ISO-IR 8859 7 1987 │ ISO/IEC 8859-7:1987 │
│ISO-IR 8859 8 1999 │ ISO/IEC 8859-8:1999 │
│ISO-IR 8859 9 1999 │ ISO/IEC 8859-9:1999 │
│ISO-IR 8859 10 1998 │ ISO/IEC 8859-10:1998 │
│ISO-IR 8859 13 1998 │ ISO/IEC 8859-13:1998 │
│ISO-IR 8859 14 1998 │ ISO/IEC 8859-14:1998 │
│ISO-IR 8859 15 1999 │ ISO/IEC 8859-15:1999 │
│ISO-IR 10646 2000 │ ISO/IEC 10646:2000 │
│ISO-IR 10646 2000 UTF-8 │ ISO/IEC 10646, UTF-8 encoding │
│BINARY │ None │
└────────────────────────┴───────────────────────────────┘
The encoding is included in an extended header for information only; when
pax is used as described in IEEE Std 1003.1-2001, it shall not translate
the file data into any other encoding. The BINARY entry indicates unencoded
binary data.
When used in write or copy mode, it is implementation-defined whether pax
includes a charset extended header record for a file.
comment
A series of characters used as a comment. All characters in the
field shall be ignored by pax.
gid The group ID of the group that owns the file, expressed as a decimal
number using digits from the ISO/IEC 646:1991 standard. This record
shall override the gid field in the following header block(s). When
used in write or copy mode, pax shall include a gid extended header
record for each file whose group ID is greater than 2097151 (octal
7777777).
gname The group of the file(s), formatted as a group name in the group
database. This record shall override the gid and gname fields in the
following header block(s), and any gid extended header record. When
used in read, copy, or list mode, pax shall translate the name from
the UTF-8 encoding in the header record to the character set appro-
priate for the group database on the receiving system. If any of the
UTF-8 characters cannot be translated, and if the -o invalid=UTF-8
option is not specified, the results are implementation-defined.
When used in write or copy mode, pax shall include a gname extended
header record for each file whose group name cannot be represented
entirely with the letters and digits of the portable character set.
linkpath
The pathname of a link being created to another file, of any type,
previously archived. This record shall override the linkname field
in the following ustar header block(s). The following ustar header
block shall determine the type of link created. If typeflag of the
following header block is 1, it shall be a hard link. If typeflag is
2, it shall be a symbolic link and the linkpath value shall be the
contents of the symbolic link. The pax utility shall translate the
name of the link (contents of the symbolic link) from the UTF-8
encoding to the character set appropriate for the local file system.
When used in write or copy mode, pax shall include a linkpath
extended header record for each link whose pathname cannot be repre-
sented entirely with the members of the portable character set other
than NUL.
mtime The file modification time of the following file(s), equivalent to
the value of the st_mtime member of the stat structure for a file,
as described in the stat(2) function. This record shall override
the mtime field in the following header block(s). The modification
time shall be restored if the process has the appropriate privilege
required to do so. The format of the shall be as described
in pax Extended Header File Times.
path The pathname of the following file(s). This record shall override
the name and prefix fields in the following header block(s). The pax
utility shall translate the pathname of the file from the UTF-8
encoding to the character set appropriate for the local file system.
When used in write or copy mode, pax shall include a path extended
header record for each file whose pathname cannot be represented
entirely with the members of the portable character set other than
NUL.
realtime.any
The keywords prefixed by "realtime." are reserved for future stan-
dardization.
security.any
The keywords prefixed by "security." are reserved for future stan-
dardization.
size The size of the file in octets, expressed as a decimal number using
digits from the ISO/IEC 646:1991 standard. This record shall over-
ride the size field in the following header block(s). When used in
write or copy mode, pax shall include a size extended header record
for each file with a size value greater than 8589934591 (octal
77777777777).
uid The user ID of the file owner, expressed as a decimal number using
digits from the ISO/IEC 646:1991 standard. This record shall over-
ride the uid field in the following header block(s). When used in
write or copy mode, pax shall include a uid extended header record
for each file whose owner ID is greater than 2097151 (octal
7777777).
uname The owner of the following file(s), formatted as a user name in the
user database. This record shall override the uid and uname fields
in the following header block(s), and any uid extended header
record. When used in read, copy, or list mode, pax shall translate
the name from the UTF-8 encoding in the header record to the charac-
ter set appropriate for the user database on the receiving system.
If any of the UTF-8 characters cannot be translated, and if the -o
invalid=UTF-8 option is not specified, the results are implementa-
tion-defined. When used in write or copy mode, pax shall include a
uname extended header record for each file whose user name cannot be
represented entirely with the letters and digits of the portable
character set.
If the field is zero length, it shall delete any header block
field, previously entered extended header value, or global extended header
value of the same name.
If a keyword in an extended header record (or in a -o option-argument)
overrides or deletes a corresponding field in the ustar header block, pax
shall ignore the contents of that header block field.
Unlike the ustar header block fields, NULs shall not delimit s; all
characters within the field shall be considered data for the field.
None of the length limitations of the ustar header block fields in ustar
Header Block shall apply to the extended header records.
pax Extended Header Keyword Precedence
This section describes the precedence in which the various header records
and fields and command line options are selected to apply to a file in the
archive. When pax is used in read or list modes, it shall determine a file
attribute in the following sequence:
1. If -o delete=keyword-prefix is used, the affected attributes
shall be determined from step 7., if applicable, or ignored
otherwise.
2. If -o keyword:= is used, the affected attributes shall be
ignored.
3. If -o keyword:=value is used, the affected attribute shall be
assigned the value.
4. If there is a typeflag x extended header record, the affected
attribute shall be assigned the . When extended
header records conflict, the last one given in the header
shall take precedence.
5. If -o keyword=value is used, the affected attribute shall be
assigned the value.
6. If there is a typeflag g global extended header record, the
affected attribute shall be assigned the . When
global extended header records conflict, the last one given
in the global header shall take precedence.
7. Otherwise, the attribute shall be determined from the ustar
header block.
pax Extended Header File Times
The pax utility shall write an mtime record for each file in write or copy
modes if the file's modification time cannot be represented exactly in the
ustar header logical record described in ustar Interchange Format. This
can occur if the time is out of ustar range, or if the file system of the
underlying implementation supports non-integer time granularities and the
time is not an integer. All of these time records shall be formatted as a
decimal representation of the time in seconds since the Epoch. If a period
('.') decimal point character is present, the digits to the right of the
point shall represent the units of a subsecond timing granularity, where
the first digit is tenths of a second and each subsequent digit is a tenth
of the previous digit. In read or copy mode, the pax utility shall truncate
the time of a file to the greatest value that is not greater than the input
header file time. In write or copy mode, the pax utility shall output a
time exactly if it can be represented exactly as a decimal number, and oth-
erwise shall generate only enough digits so that the same time shall be
recovered if the file is extracted on a system whose underlying implementa-
tion supports the same time granularity.
ustar Interchange Format
A ustar archive tape or file shall contain a series of logical records.
Each logical record shall be a fixed-size logical record of 512 octets (see
below). Although this format may be thought of as being stored on 9-track
industry-standard 12.7 mm (0.5 in) magnetic tape, other types of trans-
portable media are not excluded. Each file archived shall be represented by
a header logical record that describes the file, followed by zero or more
logical records that give the contents of the file. At the end of the ar-
chive file there shall be two 512-octet logical records filled with binary
zeros, interpreted as an end-of-archive indicator.
The logical records may be grouped for physical I/O operations, as
described under the -b blocksize and -x ustar options. Each group of logi-
cal records may be written with a single operation equivalent to the
write(2) function. On magnetic tape, the result of this write shall be a
single tape physical block. The last physical block shall always be the
full size, so logical records after the two zero logical records may con-
tain undefined data.
The header logical record shall be structured as shown in the following ta-
ble. All lengths and offsets are in decimal.
Table: ustar Header Block
┌───────────┬──────────────┬────────────────────┐
│Field Name │ Octet Offset │ Length (in Octets) │
├───────────┼──────────────┼────────────────────┤
│name │ 0 │ 100 │
│mode │ 100 │ 8 │
│uid │ 108 │ 8 │
│gid │ 116 │ 8 │
│size │ 124 │ 12 │
│mtime │ 136 │ 12 │
│chksum │ 148 │ 8 │
│typeflag │ 156 │ 1 │
│linkname │ 157 │ 100 │
│magic │ 257 │ 6 │
│version │ 263 │ 2 │
│uname │ 265 │ 32 │
│gname │ 297 │ 32 │
│devmajor │ 329 │ 8 │
│devminor │ 337 │ 8 │
│prefix │ 345 │ 155 │
└───────────┴──────────────┴────────────────────┘
All characters in the header logical record shall be represented in the
coded character set of the ISO/IEC 646:1991 standard. For maximum portabil-
ity between implementations, names should be selected from characters rep-
resented by the portable filename character set as octets with the most
significant bit zero. If an implementation supports the use of characters
outside of slash and the portable filename character set in names for
files, users, and groups, one or more implementation-defined encodings of
these characters shall be provided for interchange purposes.
However, the pax utility shall never create filenames on the local system
that cannot be accessed via the procedures described in IEEE Std
1003.1-2001. If a filename is found on the medium that would create an
invalid filename, it is implementation-defined whether the data from the
file is stored on the file hierarchy and under what name it is stored. The
pax utility may choose to ignore these files as long as it produces an
error indicating that the file is being ignored.
Each field within the header logical record is contiguous; that is, there
is no padding used. Each character on the archive medium shall be stored
contiguously.
The fields magic, uname, and gname are character strings each terminated by
a NUL character. The fields name, linkname, and prefix are NUL-terminated
character strings except when all characters in the array contain non-NUL
characters including the last character. The version field is two octets
containing the characters "00" (zero-zero). The typeflag contains a single
character. All other fields are leading zero-filled octal numbers using
digits from the ISO/IEC 646:1991 standard IRV. Each numeric field is termi-
nated by one or more or NUL characters.
The name and the prefix fields shall produce the pathname of the file. A
new pathname shall be formed, if prefix is not an empty string (its first
character is not NUL), by concatenating prefix (up to the first NUL charac-
ter), a slash character, and name; otherwise, name is used alone. In either
case, name is terminated at the first NUL character. If prefix begins with
a NUL character, it shall be ignored. In this manner, pathnames of at most
256 characters can be supported. If a pathname does not fit in the space
provided, pax shall notify the user of the error, and shall not store any
part of the file-header or data-on the medium.
The linkname field, described below, shall not use the prefix to produce a
pathname. As such, a linkname is limited to 100 characters. If the name
does not fit in the space provided, pax shall notify the user of the error,
and shall not attempt to store the link on the medium.
The mode field provides 12 bits encoded in the ISO/IEC 646:1991 standard
octal digit representation. The encoded bits shall represent the following
values:
Table: ustar mode Field
┌──────┬─────────────────┬─────────────────────────────────────────────────┐
│ Bit │ IEEE Std │ Description │
│Value │ 1003.1-2001 Bit │ │
├──────┼─────────────────┼─────────────────────────────────────────────────┤
│04000 │ S_ISUID │ Set UID on execution. │
│02000 │ S_ISGID │ Set GID on execution. │
│01000 │ │ Reserved for future standardization. │
│00400 │ S_IRUSR │ Read permission for file owner class. │
│00200 │ S_IWUSR │ Write permission for file owner class. │
│00100 │ S_IXUSR │ Execute/search permission for file owner class. │
│00040 │ S_IRGRP │ Read permission for file group class. │
│00020 │ S_IWGRP │ Write permission for file group class. │
│00010 │ S_IXGRP │ Execute/search permission for file group class. │
│00004 │ S_IROTH │ Read permission for file other class. │
│00002 │ S_IWOTH │ Write permission for file other class. │
│00001 │ S_IXOTH │ Execute/search permission for file other class. │
└──────┴─────────────────┴─────────────────────────────────────────────────┘
When appropriate privilege is required to set one of these mode bits, and
the user restoring the files from the archive does not have the appropriate
privilege, the mode bits for which the user does not have appropriate priv-
ilege shall be ignored. Some of the mode bits in the archive format are not
mentioned elsewhere in this volume of IEEE Std 1003.1-2001. If the imple-
mentation does not support those bits, they may be ignored.
The uid and gid fields are the user and group ID of the owner and group of
the file, respectively.
The size field is the size of the file in octets. If the typeflag field is
set to specify a file to be of type 1 (a link) or 2 (a symbolic link), the
size field shall be specified as zero. If the typeflag field is set to
specify a file of type 5 (directory), the size field shall be interpreted
as described under the definition of that record type. No data logical
records are stored for types 1, 2, or 5. If the typeflag field is set to 3
(character special file), 4 (block special file), or 6 (FIFO), the meaning
of the size field is unspecified by this volume of IEEE Std 1003.1-2001,
and no data logical records shall be stored on the medium. Additionally,
for type 6, the size field shall be ignored when reading. If the typeflag
field is set to any other value, the number of logical records written fol-
lowing the header shall be (size+511)/512, ignoring any fraction in the
result of the division.
The mtime field shall be the modification time of the file at the time it
was archived. It is the ISO/IEC 646:1991 standard representation of the
octal value of the modification time obtained from the stat(2) function.
The chksum field shall be the ISO/IEC 646:1991 standard IRV representation
of the octal value of the simple sum of all octets in the header logical
record. Each octet in the header shall be treated as an unsigned value.
These values shall be added to an unsigned integer, initialized to zero,
the precision of which is not less than 17 bits. When calculating the
checksum, the chksum field is treated as if it were all spaces.
The typeflag field specifies the type of file archived. If a particular
implementation does not recognize the type, or the user does not have
appropriate privilege to create that type, the file shall be extracted as
if it were a regular file if the file type is defined to have a meaning for
the size field that could cause data logical records to be written on the
medium (see the previous description for size). If conversion to a regular
file occurs, the pax utility shall produce an error indicating that the
conversion took place. All of the typeflag fields shall be coded in the
ISO/IEC 646:1991 standard IRV:
0 Represents a regular file. For backwards-compatibility, a typeflag
value of binary zero ('\0') should be recognized as meaning a regu-
lar file when extracting files from the archive. Archives written
with this version of the archive file format create regular files
with a typefla value of the ISO/IEC 646:1991 standard IRV '0'.
1 Represents a file linked to another file, of any type, previously
archived. Such files are identified by having the same device and
file serial numbers, and pathnames that refer to different directory
entries. All such files shall be archived as linked files. The
linked-to name is specified in the linkname field with a NUL-charac-
ter terminator if it is less than 100 octets in length.
2 Represents a symbolic link. The contents of the symbolic link shall
be stored in the linkname field.
3,4 Represent character special files and block special files respec-
tively. In this case the devmajor and devminor fields shall contain
information defining the device, the format of which is unspecified
by this volume of IEEE Std 1003.1-2001. Implementations may map the
device specifications to their own local specification or may ignore
the entry.
5 Specifies a directory or subdirectory. On systems where disk alloca-
tion is performed on a directory basis, the size field shall contain
the maximum number of octets (which may be rounded to the nearest
disk block allocation unit) that the directory may hold. A size
field of zero indicates no such limiting. Systems that do not sup-
port limiting in this manner should ignore the size field.
6 Specifies a FIFO special file. Note that the archiving of a FIFO
file archives the existence of this file and not its contents.
7 Reserved to represent a file to which an implementation has associ-
ated some high-performance attribute. Implementations without such
extensions should treat this file as a regular file (type 0).
A-Z The letters 'A' to 'Z', inclusive, are reserved for custom implemen-
tations. All other values are reserved for future versions of IEEE
Std 1003.1-2001.
It is unspecified whether files with pathnames that refer to the same
directory entry are archived as linked files or as separate files. If they
are archived as linked files, this means that attempting to extract both
pathnames from the resulting archive will always cause an error (unless the
-u option is used) because the link cannot be created.
It is unspecified whether files with the same device and file serial num-
bers being appended to an archive are treated as linked files to members
that were in the archive before the append.
Attempts to archive a socket using ustar interchange format shall produce a
diagnostic message. Handling of other file types is implementation-defined.
The magic field is the specification that this archive was output in this
archive format. If this field contains ustar (the five characters from the
ISO/IEC 646:1991 standard IRV shown followed by NUL), the uname and gname
fields shall contain the ISO/IEC 646:1991 standard IRV representation of
the owner and group of the file, respectively (truncated to fit, if neces-
sary). When the file is restored by a privileged, protection-preserving
version of the utility, the user and group databases shall be scanned for
these names. If found, the user and group IDs contained within these files
shall be used rather than the values contained within the uid and gid
fields.
cpio Interchange Format
The octet-oriented cpio archive format shall be a series of entries, each
comprising a header that describes the file, the name of the file, and then
the contents of the file.
An archive may be recorded as a series of fixed-size blocks of octets. This
blocking shall be used only to make physical I/O more efficient. The last
group of blocks shall always be at the full size.
For the octet-oriented cpio archive format, the individual entry informa-
tion shall be in the order indicated and described by the following table;
see also the header.
Table: Octet-Oriented cpio Archive Entry
┌─────────────────────┬────────────────────┬─────────────────┐
│ Header Field Name │ Length (in Octets) │ Interpreted as │
├─────────────────────┼────────────────────┼─────────────────┤
│c_magic │ 6 │ Octal number │
│c_dev │ 6 │ Octal number │
│c_ino │ 6 │ Octal number │
│c_mode │ 6 │ Octal number │
│c_uid │ 6 │ Octal number │
│c_gid │ 6 │ Octal number │
│c_nlink │ 6 │ Octal number │
│c_rdev │ 6 │ Octal number │
│c_mtime │ 11 │ Octal number │
│c_namesize │ 6 │ Octal number │
│c_filesize │ 11 │ Octal number │
│ │ │ │
│Filename Field Name │ Length │ Interpreted as │
│c_name │ c_namesize │ Pathname string │
│ │ │ │
│File Data Field Name │ Length │ Interpreted as │
│c_filedata │ c_filesize │ Data │
└─────────────────────┴────────────────────┴─────────────────┘
cpio Header
For each file in the archive, a header as defined previously shall be writ-
ten. The information in the header fields is written as streams of the
ISO/IEC 646:1991 standard characters interpreted as octal numbers. The
octal numbers shall be extended to the necessary length by appending the
ISO/IEC 646:1991 standard IRV zeros at the most-significant-digit end of
the number; the result is written to the most-significant digit of the
stream of octets first. The fields shall be interpreted as follows:
c_magic
Identify the archive as being a transportable archive by containing
the identifying value "070707".
c_dev, c_ino
Contains values that uniquely identify the file within the archive
(that is, no files contain the same pair of c_dev and c_ino values
unless they are links to the same file). The values shall be deter-
mined in an unspecified manner.
c_mode Contains the file type and access permissions as defined in the fol-
lowing table.
Table: Values for cpio c_mode Field
┌──────────────────────┬─────────┬────────────────────────┐
│File Permissions Name │ Value │ Indicates │
├──────────────────────┼─────────┼────────────────────────┤
│C_IRUSR │ 000400 │ Read by owner │
│C_IWUSR │ 000200 │ Write by owner │
│C_IXUSR │ 000100 │ Execute by owner │
│C_IRGRP │ 000040 │ Read by group │
│C_IWGRP │ 000020 │ Write by group │
│C_IXGRP │ 000010 │ Execute by group │
│C_IROTH │ 000004 │ Read by others │
│C_IWOTH │ 000002 │ Write by others │
│C_IXOTH │ 000001 │ Execute by others │
│C_ISUID │ 004000 │ Set uid │
│C_ISGID │ 002000 │ Set gid │
│C_ISVTX │ 001000 │ Reserved │
├──────────────────────┼─────────┼────────────────────────┤
│File Type Name │ Value │ Indicates │
├──────────────────────┼─────────┼────────────────────────┤
│C_ISDIR │ 0040000 │ Directory │
│C_ISFIFO │ 0010000 │ FIFO │
│C_ISREG │ 0100000 │ Regular file │
│C_ISLNK │ 0120000 │ Symbolic link │
│C_ISBLK │ 0060000 │ Block special file │
│C_ISCHR │ 0020000 │ Character special file │
│C_ISSOCK │ 0140000 │ Socket │
│C_ISCTG │ 0110000 │ Reserved │
└──────────────────────┴─────────┴────────────────────────┘
Directories, FIFOs, symbolic links, and regular files shall be sup-
ported on a system conforming to this volume of IEEE Std
1003.1-2001; additional values defined previously are reserved for
compatibility with existing systems. Additional file types may be
supported; however, such files should not be written to archives
intended to be transported to other systems.
c_uid Contains the user ID of the owner.
c_gid Contains the group ID of the group.
c_nlink
Contains a number greater than or equal to the number of links in
the archive referencing the file. If the -a option is used to append
to a cpio archive, then the pax utility need not account for the
files in the existing part of the archive when calculating the
c_nlink values for the appended part of the archive, and need not
alter the c_nlink values in the existing part of the archive if
additional files with the same c_dev and c_ino values are appended
to the archive.
c_rdev Contains implementation-defined information for character or block
special files.
c_mtime
Contains the latest time of modification of the file at the time the
archive was created.
c_namesize
Contains the length of the pathname, including the terminating NUL
character.
c_filesize
Contains the length of the file in octets. This shall be the length
of the data section following the header structure.
cpio Filename
The c_name field shall contain the pathname of the file. The length of this
field in octets is the value of c_namesize.
If a filename is found on the medium that would create an invalid pathname,
it is implementation-defined whether the data from the file is stored on
the file hierarchy and under what name it is stored.
All characters shall be represented in the ISO/IEC 646:1991 standard IRV.
For maximum portability between implementations, names should be selected
from characters represented by the portable filename character set as
octets with the most significant bit zero. If an implementation supports
the use of characters outside the portable filename character set in names
for files, users, and groups, one or more implementation-defined encodings
of these characters shall be provided for interchange purposes. However,
the pax utility shall never create filenames on the local system that can-
not be accessed via the procedures described previously in this volume of
IEEE Std 1003.1-2001. If a filename is found on the medium that would cre-
ate an invalid filename, it is implementation-defined whether the data from
the file is stored on the local file system and under what name it is
stored. The pax utility may choose to ignore these files as long as it pro-
duces an error indicating that the file is being ignored.
cpio File Data
Following c_name, there shall be c_filesize octets of data. Interpretation
of such data occurs in a manner dependent on the file. If c_filesize is
zero, no data shall be contained in c_filedata.
When restoring from an archive:
· If the user does not have the appropriate privilege to create a file
of the specified type, pax shall ignore the entry and write an error
message to standard error.
· Only regular files have data to be restored. Presuming a regular
file meets any selection criteria that might be imposed on the for-
mat-reading utility by the user, such data shall be restored.
· If a user does not have appropriate privilege to set a particular
mode flag, the flag shall be ignored. Some of the mode flags in the
archive format are not mentioned elsewhere in this volume of IEEE
Std 1003.1-2001. If the implementation does not support those flags,
they may be ignored.
cpio Special Entries
FIFO special files, directories, and the trailer shall be recorded with
c_filesize equal to zero. For other special files, c_filesize is unspeci-
fied by this volume of IEEE Std 1003.1-2001. The header for the next file
entry in the archive shall be written directly after the last octet of the
file entry preceding it. A header denoting the filename TRAILER!!! shall
indicate the end of the archive; the contents of octets in the last block
of the archive following such a header are undefined.
EXIT STATUS
The following exit values shall be returned:
0 All files were processed successfully.
>0 An error occurred.
CONSEQUENCES OF ERRORS
If pax cannot create a file or a link when reading an archive or cannot
find a file when writing an archive, or cannot preserve the user ID, group
ID, or file mode when the -p option is specified, a diagnostic message
shall be written to standard error and a non-zero exit status shall be
returned, but processing shall continue. In the case where pax cannot cre-
ate a link to a file, pax shall not, by default, create a second copy of
the file.
If the extraction of a file from an archive is prematurely terminated by a
signal or error, pax may have only partially extracted the file or (if the
-n option was not specified) may have extracted a file of the same name as
that specified by the user, but which is not the file the user wanted.
Additionally, the file modes of extracted directories may have additional
bits from the S_IRWXU mask set as well as incorrect modification and access
times.
_________________________________________________________________
The following sections are informative.
APPLICATION USAGE
Caution is advised when using the -a option to append to a cpio format ar-
chive. If any of the files being appended happen to be given the same c_dev
and c_ino values as a file in the existing part of the archive, then they
may be treated as links to that file on extraction. Thus, it is risky to
use -a with cpio format except when it is done on the same system that the
original archive was created on, and with the same pax utility, and in the
knowledge that there has been little or no file system activity since the
original archive was created that could lead to any of the files appended
being given the same c_dev and c_ino values as an unrelated file in the
existing part of the archive. Also, when (intentionally) appending addi-
tional links to a file in the existing part of the archive, the c_nlink
values in the modified archive can be smaller than the number of links to
the file in the archive, which may mean that the links are not preserved on
extraction.
The -p (privileges) option was invented to reconcile differences between
historical tar and cpio implementations. In particular, the two utilities
use -m in diametrically opposed ways. The -p option also provides a consis-
tent means of extending the ways in which future file attributes can be
addressed, such as for enhanced security systems or high-performance files.
Although it may seem complex, there are really two modes that are most com-
monly used:
-p e ``Preserve everything". This would be used by the historical supe-
ruser, someone with all the appropriate privileges, to preserve all
aspects of the files as they are recorded in the archive. The e flag
is the sum of o and p, and other implementation-defined attributes.
-p p ``Preserve" the file mode bits. This would be used by the user with
regular privileges who wished to preserve aspects of the file other
than the ownership. The file times are preserved by default, but two
other flags are offered to disable these and use the time of extrac-
tion.
The one pathname per line format of standard input precludes pathnames con-
taining s. Although such pathnames violate the portable filename
guidelines, they may exist and their presence may inhibit usage of pax
within shell scripts. This problem is inherited from historical archive
programs. The problem can be avoided by listing filename arguments on the
command line instead of on standard input.
It is almost certain that appropriate privileges are required for pax to
accomplish parts of this volume of IEEE Std 1003.1-2001. Specifically,
creating files of type block special or character special, restoring file
access times unless the files are owned by the user (the -t option), or
preserving file owner, group, and mode (the -p option) all probably require
appropriate privileges.
In read mode, implementations are permitted to overwrite files when the ar-
chive has multiple members with the same name. This may fail if permissions
on the first version of the file do not permit it to be overwritten.
The cpio and ustar formats can only support files up to 8589934592 bytes (8
* 2^30) in size.
EXAMPLES
The following command:
pax -w -f /dev/rmt/1m .
copies the contents of the current directory to tape drive 1, medium den-
sity (assuming historical System V device naming procedures-the historical
BSD device name would be /dev/rmt9).
The following commands:
mkdir newdirpax -rw olddir newdir
copy the olddir directory hierarchy to newdir.
pax -r -s ',^//*usr//*,,' -f a.pax
reads the archive a.pax, with all files rooted in /usr in the archive
extracted relative to the current directory.
Using the option:
-o listopt="%M %(atime)T %(size)D %(name)s"
overrides the default output description in Standard Output and instead
writes:
-rw-rw--- Jan 12 15:53 1492 /usr/foo/bar
Using the options:
-o listopt='%L\t%(size)D\n%.7' \
-o listopt='(name)s\n%(atime)T\n%T'
overrides the default output description in Standard Output and instead
writes:
/usr/foo/bar -> /tmp 1492
/usr/fo
Jan 12 1991
Jan 31 15:53
RATIONALE
The pax utility was new for the ISO POSIX-2:1993 standard. It represents a
peaceful compromise between advocates of the historical tar and cpio utili-
ties.
A fundamental difference between cpio and tar was in the way directories
were treated. The cpio utility did not treat directories differently from
other files, and to select a directory and its contents required that each
file in the hierarchy be explicitly specified. For tar, a directory matched
every file in the file hierarchy it rooted.
The pax utility offers both interfaces; by default, directories map into
the file hierarchy they root. The -d option causes pax to skip any file not
explicitly referenced, as cpio historically did. The tar - style behavior
was chosen as the default because it was believed that this was the more
common usage and because tar is the more commonly available interface, as
it was historically provided on both System V and BSD implementations.
The data interchange format specification in this volume of IEEE Std
1003.1-2001 requires that processes with "appropriate privileges" shall
always restore the ownership and permissions of extracted files exactly as
archived. If viewed from the historic equivalence between superuser and
"appropriate privileges", there are two problems with this requirement.
First, users running as superusers may unknowingly set dangerous permis-
sions on extracted files. Second, it is needlessly limiting, in that supe-
rusers cannot extract files and own them as superuser unless the archive
was created by the superuser. (It should be noted that restoration of own-
erships and permissions for the superuser, by default, is historical prac-
tice in cpio, but not in tar.) In order to avoid these two problems, the
pax specification has an additional "privilege" mechanism, the -p option.
Only a pax invocation with the privileges needed, and which has the -p
option set using the e specification character, has the "appropriate privi-
lege" to restore full ownership and permission information.
Note also that this volume of IEEE Std 1003.1-2001 requires that the file
ownership and access permissions shall be set, on extraction, in the same
fashion as the creat(2) function when provided with the mode stored in the
archive. This means that the file creation mask of the user is applied to
the file permissions.
Users should note that directories may be created by pax while extracting
files with permissions that are different from those that existed at the
time the archive was created. When extracting sensitive information into a
directory hierarchy that no longer exists, users are encouraged to set
their file creation mask appropriately to protect these files during
extraction.
The table of contents output is written to standard output to facilitate
pipeline processing.
An early proposal had hard links displaying for all pathnames. This was
removed because it complicates the output of the case where -v is not spec-
ified and does not match historical cpio usage. The hard-link information
is available in the -v display.
The description of the -l option allows implementations to make hard links
to symbolic links. IEEE Std 1003.1-2001 does not specify any way to create
a hard link to a symbolic link, but many implementations provide this capa-
bility as an extension. If there are hard links to symbolic links when an
archive is created, the implementation is required to archive the hard link
in the archive (unless -H or -L is specified). When in read mode and in
copy mode, implementations supporting hard links to symbolic links should
use them when appropriate.
The archive formats inherited from the POSIX.1-1990 standard have certain
restrictions that have been brought along from historical usage. For exam-
ple, there are restrictions on the length of pathnames stored in the ar-
chive. When pax is used in copy (-rw) mode (copying directory hierarchies),
the ability to use extensions from the -x pax format overcomes these
restrictions.
The default blocksize value of 5120 bytes for cpio was selected because it
is one of the standard block-size values for cpio, set when the -B option
is specified. (The other default block-size value for cpio is 512 bytes,
and this was considered to be too small.) The default block value of 10240
bytes for tar was selected because that is the standard block-size value
for BSD tar. The maximum block size of 32256 bytes (2^15-512 bytes) is the
largest multiple of 512 bytes that fits into a signed 16-bit tape con-
troller transfer register. There are known limitations in some historical
systems that would prevent larger blocks from being accepted. Historical
values were chosen to improve compatibility with historical scripts using
dd(1) or similar utilities to manipulate archives. Also, default block
sizes for any file type other than character special file has been deleted
from this volume of IEEE Std 1003.1-2001 as unimportant and not likely to
affect the structure of the resulting archive.
Implementations are permitted to modify the block-size value based on the
archive format or the device to which the archive is being written. This is
to provide implementations with the opportunity to take advantage of spe-
cial types of devices, and it should not be used without a great deal of
consideration as it almost certainly decreases archive portability.
The intended use of the -n option was to permit extraction of one or more
files from the archive without processing the entire archive. This was
viewed by the standard developers as offering significant performance
advantages over historical implementations. The -n option in early propos-
als had three effects; the first was to cause special characters in pat-
terns to not be treated specially. The second was to cause only the first
file that matched a pattern to be extracted. The third was to cause pax to
write a diagnostic message to standard error when no file was found match-
ing a specified pattern. Only the second behavior is retained by this vol-
ume of IEEE Std 1003.1-2001, for many reasons. First, it is in general not
acceptable for a single option to have multiple effects. Second, the abil-
ity to make pattern matching characters act as normal characters is useful
for parts of pax other than file extraction. Third, a finer degree of con-
trol over the special characters is useful because users may wish to nor-
malize only a single special character in a single filename. Fourth, given
a more general escape mechanism, the previous behavior of the -n option can
be easily obtained using the -s option or a sed script. Finally, writing a
diagnostic message when a pattern specified by the user is unmatched by any
file is useful behavior in all cases.
In this version, the -n was removed from the copy mode synopsis of pax; it
is inapplicable because there are no pattern operands specified in this
mode.
There is another method than pax for copying subtrees in IEEE Std
1003.1-2001 described as part of the cp(1) utility. Both methods are his-
torical practice: cp(1) provides a simpler, more intuitive interface, while
pax offers a finer granularity of control. Each provides additional func-
tionality to the other; in particular, pax maintains the hard-link struc-
ture of the hierarchy while cp(1) does not. It is the intention of the
standard developers that the results be similar (using appropriate option
combinations in both utilities). The results are not required to be identi-
cal; there seemed insufficient gain to applications to balance the diffi-
culty of implementations having to guarantee that the results would be
exactly identical.
A single archive may span more than one file. It is suggested that imple-
mentations provide informative messages to the user on standard error when-
ever the archive file is changed.
The -d option (do not create intermediate directories not listed in the ar-
chive) found in early proposals was originally provided as a complement to
the historic -d option of cpio. It has been deleted.
The -s option in early proposals specified a subset of the substitution
command from the ed utility. As there was no reason for only a subset to be
supported, the -s option is now compatible with the current ed specifica-
tion. Since the delimiter can be any non-null character, the following
usage with single spaces is valid:
pax -s " foo bar " ...
The -t description is worded so as to note that this may cause the access
time update caused by some other activity (which occurs while the file is
being read) to be overwritten.
The default behavior of pax with regard to file modification times is the
same as historical implementations of tar. It is not the historical behav-
ior of cpio.
Because the -i option uses /dev/tty, utilities without a controlling termi-
nal are not able to use this option.
The -y option, found in early proposals, has been deleted because a line
containing a single period for the -i option has equivalent functionality.
The special lines for the -i option (a single period and the empty line)
are historical practice in cpio.
In early drafts, a -e charmap option was included to increase portability
of files between systems using different coded character sets. This option
was omitted because it was apparent that consensus could not be formed for
it. In this version, the use of UTF-8 should be an adequate substitute.
The -k option was added to address international concerns about the dangers
involved in the character set transformations of -e (if the target charac-
ter set were different from the source, the filenames might be transformed
into names matching existing files) and also was made more general to pro-
tect files transferred between file systems with different {NAME_MAX} val-
ues (truncating a filename on a smaller system might also inadvertently
overwrite existing files). As stated, it prevents any overwriting, even if
the target file is older than the source. This version adds more granular-
ity of options to solve this problem by introducing the -o invalid=option -
specifically the UTF-8 action. (Note that an existing file that is named
with a UTF-8 encoding is still subject to overwriting in this case. The -k
option closes that loophole.)
Some of the file characteristics referenced in this volume of IEEE Std
1003.1-2001 might not be supported by some archive formats. For example,
neither the tar nor cpio formats contain the file access time. For this
reason, the e specification character has been provided, intended to cause
all file characteristics specified in the archive to be retained.
It is required that extracted directories, by default, have their access
and modification times and permissions set to the values specified in the
archive. This has obvious problems in that the directories are almost cer-
tainly modified after being extracted and that directory permissions may
not permit file creation. One possible solution is to create directories
with the mode specified in the archive, as modified by the umask of the
user, with sufficient permissions to allow file creation. After all files
have been extracted, pax would then reset the access and modification times
and permissions as necessary.
The list-mode formatting description borrows heavily from the one defined
by the printf(1) utility. However, since there is no separate operand list
to get conversion arguments, the format was extended to allow specifying
the name of the conversion argument as part of the conversion specifica-
tion.
The T conversion specifier allows time fields to be displayed in any of the
date formats. Unlike the ls(1) utility, pax does not adjust the format when
the date is less than six months in the past. This makes parsing the output
more predictable.
The D conversion specifier handles the ability to display the major/minor
or file size, as with ls(1), by using %-8(size)D.
The L conversion specifier handles the ls display for symbolic links.
Conversion specifiers were added to generate existing known types used for
ls(1).
pax Interchange Format
The new POSIX data interchange format was developed primarily to satisfy
international concerns that the ustar and cpio formats did not provide for
file, user, and group names encoded in characters outside a subset of the
ISO/IEC 646:1991 standard. The standard developers realized that this new
POSIX data interchange format should be very extensible because there were
other requirements they foresaw in the near future:
· Support international character encodings and locale information
· Support security information (ACLs, and so on)
· Support future file types, such as realtime or contiguous files
· Include data areas for implementation use
· Support systems with words larger than 32 bits and timers with sub-
second granularity
The following were not goals for this format because these are better han-
dled by separate utilities or are inappropriate for a portable format:
· Encryption
· Compression
· Data translation between locales and codesets
· inode storage
The format chosen to support the goals is an extension of the ustar format.
Of the two formats previously available, only the ustar format was selected
for extensions because:
· It was easier to extend in an upwards-compatible way. It offered
version flags and header block type fields with room for future
standardization. The cpio format, while possessing a more flexible
file naming methodology, could not be extended without breaking some
theoretical implementation or using a dummy filename that could be a
legitimate filename.
· Industry experience since the original "tar wars" fought in develop-
ing the ISO POSIX-1 standard has clearly been in favor of the ustar
format, which is generally the default output format selected for
pax implementations on new systems.
The new format was designed with one additional goal in mind: reasonable
behavior when an older tar or pax utility happened to read an archive.
Since the POSIX.1-1990 standard mandated that a "format-reading utility"
had to treat unrecognized typeflag values as regular files, this allowed
the format to include all the extended information in a pseudo-regular file
that preceded each real file. An option is given that allows the archive
creator to set up reasonable names for these files on the older systems.
Also, the normative text suggests that reasonable file access values be
used for this ustar header block. Making these header files inaccessible
for convenient reading and deleting would not be reasonable. File permis-
sions of 600 or 700 are suggested.
The ustar typeflag field was used to accommodate the additional functional-
ity of the new format rather than magic or version because the POSIX.1-1990
standard (and, by reference, the previous version of pax), mandated the
behavior of the format-reading utility when it encountered an unknown type-
flag, but was silent about the other two fields.
Early proposals of the first revision to IEEE Std 1003.1-2001 contained a
proposed archive format that was based on compatibility with the standard
for tape files (ISO 1001, similar to the format used historically on many
mainframes and minicomputers). This format was overly complex and required
considerable overhead in volume and header records. Furthermore, the stan-
dard developers felt that it would not be acceptable to the community of
POSIX developers, so it was later changed to be a format more closely
related to historical practice on POSIX systems.
The prefix and name split of pathnames in ustar was replaced by the single
path extended header record for simplicity.
The concept of a global extended header (typeflag g) was controversial. If
this were applied to an archive being recorded on magnetic tape, a few
unreadable blocks at the beginning of the tape could be a serious problem;
a utility attempting to extract as many files as possible from a damaged
archive could lose a large percentage of file header information in this
case. However, if the archive were on a reliable medium, such as a CD-ROM,
the global extended header offers considerable potential size reductions by
eliminating redundant information. Thus, the text warns against using the
global method for unreliable media and provides a method for implanting
global information in the extended header for each file, rather than in the
typeflag g records.
No facility for data translation or filtering on a per-file basis is
included because the standard developers could not invent an interface that
would allow this in an efficient manner. If a filter, such as encryption or
compression, is to be applied to all the files, it is more efficient to
apply the filter to the entire archive as a single file. The standard
developers considered interfaces that would invoke a shell script for each
file going into or out of the archive, but the system overhead in this
approach was considered to be too high.
One such approach would be to have filter= records that give a pathname for
an executable. When the program is invoked, the file and archive would be
open for standard input/output and all the header fields would be available
as environment variables or command-line arguments. The standard developers
did discuss such schemes, but they were omitted from IEEE Std 1003.1-2001
due to concerns about excessive overhead. Also, the program itself would
need to be in the archive if it were to be used portably.
There is currently no portable means of identifying the character set(s)
used for a file in the file system. Therefore, pax has not been given a
mechanism to generate charset records automatically. The only portable
means of doing this is for the user to write the archive using the -o
charset=string command line option. This assumes that all of the files in
the archive use the same encoding. The "implementation-defined" text is
included to allow for a system that can identify the encodings used for
each of its files.
The table of standards that accompanies the charset record description is
acknowledged to be very limited. Only a limited number of character set
standards is reasonable for maximal interchange. Any character set is, of
course, possible by prior agreement. It was suggested that EBCDIC be
listed, but it was omitted because it is not defined by a formal standard.
Formal standards, and then only those with reasonably large followings, can
be included here, simply as a matter of practicality. The s repre-
sent names of officially registered character sets in the format required
by the ISO 2375:1985 standard.
The normal comma or -separated list rules are not followed in the
case of keyword options to allow ease of argument parsing for getopts.
Further information on character encodings is in pax Archive Character Set
Encoding/Decoding.
The standard developers have reserved keyword name space for vendor exten-
sions. It is suggested that the format to be used is:
VENDOR.keyword
where VENDOR is the name of the vendor or organization in all uppercase
letters. It is further suggested that the keyword following the period be
named differently than any of the standard keywords so that it could be
used for future standardization, if appropriate, by omitting the VENDOR
prefix.
The field in the extended header record was included to make it
simpler to step through the records, even if a record contains an unknown
format (to a particular pax) with complex interactions of special charac-
ters. It also provides a minor integrity checkpoint within the records to
aid a program attempting to recover files from a damaged archive.
There are no extended header versions of the devmajor and devminor fields
because the unspecified format ustar header field should be sufficient. If
they are not, vendor-specific extended keywords (such as VENDOR.devmajor)
should be used.
Device and i-number labeling of files was not adopted from cpio; files are
interchanged strictly on a symbolic name basis, as in ustar.
Just as with the ustar format descriptions, the new format makes no special
arrangements for multi-volume archives. Each of the pax archive types is
assumed to be inside a single POSIX file and splitting that file over mul-
tiple volumes (diskettes, tape cartridges, and so on), processing their
labels, and mounting each in the proper sequence are considered to be
implementation details that cannot be described portably.
The pax format is intended for interchange, not only for backup on a single
(family of) systems. It is not as densely packed as might be possible for
backup:
· It contains information as coded characters that could be coded in
binary.
· It identifies extended records with name fields that could be omit-
ted in favor of a fixed-field layout.
· It translates names into a portable character set and identifies
locale-related information, both of which are probably unnecessary
for backup.
The requirements on restoring from an archive are slightly different from
the historical wording, allowing for non-monolithic privilege to bring for-
ward as much as possible. In particular, attributes such as "high perfor-
mance file" might be broadly but not universally granted while set-user-ID
or chown(2) might be much more restricted. There is no implication in IEEE
Std 1003.1-2001 that the security information be honored after it is
restored to the file hierarchy, in spite of what might be improperly
inferred by the silence on that topic. That is a topic for another stan-
dard.
Links are recorded in the fashion described here because a link can be to
any file type. It is desirable in general to be able to restore part of an
archive selectively and restore all of those files completely. If the data
is not associated with each link, it is not possible to do this. However,
the data associated with a file can be large, and when selective restora-
tion is not needed, this can be a significant burden. The archive is struc-
tured so that files that have no associated data can always be restored by
the name of any link name of any link, and the user may choose whether data
is recorded with each instance of a file that contains data. The format
permits mixing of both types of links in a single archive; this can be done
for special needs, and pax is expected to interpret such archives on input
properly, despite the fact that there is no pax option that would force
this mixed case on output. (When -o linkdata is used, the output must con-
tain the duplicate data, but the implementation is free to include it or
omit it when -o linkdata is not used.)
The time values are included as extended header records for those implemen-
tations needing more than the eleven octal digits allowed by the ustar for-
mat. Portable file timestamps cannot be negative. If pax encounters a file
with a negative timestamp in copy or write mode, it can reject the file,
substitute a non-negative timestamp, or generate a non-portable timestamp
with a leading '-'. Even though some implementations can support finer
file-time granularities than seconds, the normative text requires support
only for seconds since the Epoch because the ISO POSIX-1 standard states
them that way. The ustar format includes only mtime; the new format adds
atime and ctime for symmetry. The atime access time restored to the file
system will be affected by the -p a and -p e options. The ctime creation
time (actually inode modification time) is described with "appropriate
privilege" so that it can be ignored when writing to the file system. POSIX
does not provide a portable means to change file creation time. Nothing is
intended to prevent a non-portable implementation of pax from restoring the
value.
The gid, size, and uid extended header records were included to allow
expansion beyond the sizes specified in the regular tar header. New file
system architectures are emerging that will exhaust the 12-digit size
field. There are probably not many systems requiring more than 8 digits for
user and group IDs, but the extended header values were included for com-
pleteness, allowing overrides for all of the decimal values in the tar
header.
The standard developers intended to describe the effective results of pax
with regard to file ownerships and permissions; implementations are not
restricted in timing or sequencing the restoration of such, provided the
results are as specified.
Much of the text describing the extended headers refers to use in "write or
copy modes". The copy mode references are due to the normative text: "The
effect of the copy shall be as if the copied files were written to an ar-
chive file and then subsequently extracted ...". There is certainly no way
to test whether pax is actually generating the extended headers in copy
mode, but the effects must be as if it had.
pax Archive Character Set Encoding/Decoding
There is a need to exchange archives of files between systems of different
native codesets. Filenames, group names, and user names must be preserved
to the fullest extent possible when an archive is read on the receiving
platform. Translation of the contents of files is not within the scope of
the pax utility.
There will also be the need to represent characters that are not available
on the receiving platform. These unsupported characters cannot be automati-
cally folded to the local set of characters due to the chance of colli-
sions. This could result in overwriting previous extracted files from the
archive or pre-existing files on the system.
For these reasons, the codeset used to represent characters within the
extended header records of the pax archive must be sufficiently rich to
handle all commonly used character sets. The fields requiring translation
include, at a minimum, filenames, user names, group names, and link path-
names. Implementations may wish to have localized extended keywords that
use non-portable characters.
The standard developers considered the following options:
· The archive creator specifies the well-defined name of the source
codeset. The receiver must then recognize the codeset name and per-
form the appropriate translations to the destination codeset.
· The archive creator includes within the archive the character map-
ping table for the source codeset used to encode extended header
records. The receiver must then read the character mapping table and
perform the appropriate translations to the destination codeset.
· The archive creator translates the extended header records in the
source codeset into a canonical form. The receiver must then perform
the appropriate translations to the destination codeset.
The approach that incorporates the name of the source codeset poses the
problem of codeset name registration, and makes the archive useless to pax
archive decoders that do not recognize that codeset.
Because parts of an archive may be corrupted, the standard developers felt
that including the character map of the source codeset was too fragile. The
loss of this one key component could result in making the entire archive
useless. (The difference between this and the global extended header deci-
sion was that the latter has a workaround-duplicating extended header
records on unreliable media-but this would be too burdensome for large
character set maps.)
Both of the above approaches also put an undue burden on the pax archive
receiver to handle the cross-product of all source and destination code-
sets.
To simplify the translation from the source codeset to the canonical form
and from the canonical form to the destination codeset, the standard devel-
opers decided that the internal representation should be a stateless encod-
ing. A stateless encoding is one where each codepoint has the same meaning,
without regard to the decoder being in a specific state. An example of a
stateful encoding would be the Japanese Shift-JIS; an example of a state-
less encoding would be the ISO/IEC 646:1991 standard (equivalent to 7-bit
ASCII).
For these reasons, the standard developers decided to adopt a canonical
format for the representation of file information strings. The obvious,
well-endorsed candidate is the ISO/IEC 10646-1:2000 standard (based in part
on Unicode), which can be used to represent the characters of virtually all
standardized character sets. The standard developers initially agreed upon
using UCS2 (16-bit Unicode) as the internal representation. This repertoire
of characters provides a sufficiently rich set to represent all commonly-
used codesets.
However, the standard developers found that the 16-bit Unicode representa-
tion had some problems. It forced the issue of standardizing byte ordering.
The 2-byte length of each character made the extended header records twice
as long for the case of strings coded entirely from historical 7-bit ASCII.
For these reasons, the standard developers chose the UTF-8 defined in the
ISO/IEC 10646-1:2000 standard. This multi-byte representation encodes UCS2
or UCS4 characters reliably and deterministically, eliminating the need for
a canonical byte ordering. In addition, NUL octets and other characters
possibly confusing to POSIX file systems do not appear, except to represent
themselves. It was realized that certain national codesets take up more
space after the encoding, due to their placement within the UCS range; it
was felt that the usefulness of the encoding of the names outweighs the
disadvantage of size increase for file, user, and group names.
The encoding of UTF-8 is as follows:
UCS4 Hex Encoding UTF-8 Binary Encoding
00000000-0000007F 0xxxxxxx
00000080-000007FF 110xxxxx 10xxxxxx
00000800-0000FFFF 1110xxxx 10xxxxxx 10xxxxxx
00010000-001FFFFF 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
00200000-03FFFFFF 111110xx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
04000000-7FFFFFFF 1111110x 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
where each 'x' represents a bit value from the character being translated.
ustar Interchange Format
The description of the ustar format reflects numerous enhancements over
pre-1988 versions of the historical tar utility. The goal of these changes
was not only to provide the functional enhancements desired, but also to
retain compatibility between new and old versions. This compatibility has
been retained. Archives written using the old archive format are compatible
with the new format.
Implementors should be aware that the previous file format did not include
a mechanism to archive directory type files. For this reason, the conven-
tion of using a filename ending with slash was adopted to specify a direc-
tory on the archive.
The total size of the name and prefix fields have been set to meet the min-
imum requirements for {PATH_MAX} If a pathname will fit within the name
field, it is recommended that the pathname be stored there without the use
of the prefix field. Although the name field is known to be too small to
contain {PATH_MAX} characters, the value was not changed in this version of
the archive file format to retain backwards-compatibility, and instead the
prefix was introduced. Also, because of the earlier version of the format,
there is no way to remove the restriction on the linkname field being lim-
ited in size to just that of the name field.
The size field is required to be meaningful in all implementation exten-
sions, although it could be zero. This is required so that the data blocks
can always be properly counted.
It is suggested that if device special files need to be represented that
cannot be represented in the standard format, that one of the extension
types (A-Z) be used, and that the additional information for the special
file be represented as data and be reflected in the size field.
Attempting to restore a special file type, where it is converted to ordi-
nary data and conflicts with an existing filename, need not be specially
detected by the utility. If run as an ordinary user, pax should not be able
to overwrite the entries in, for example, /dev in any case (whether the
file is converted to another type or not). If run as a privileged user, it
should be able to do so, and it would be considered a bug if it did not.
The same is true of ordinary data files and similarly named special files;
it is impossible to anticipate the needs of the user (who could really
intend to overwrite the file), so the behavior should be predictable (and
thus regular) and rely on the protection system as required.
The value 7 in the typeflag field is intended to define how contiguous
files can be stored in a ustar archive. IEEE Std 1003.1-2001 does not
require the contiguous file extension, but does define a standard way of
archiving such files so that all conforming systems can interpret these
file types in a meaningful and consistent manner. On a system that does not
support extended file types, the pax utility should do the best it can with
the file and go on to the next.
The file protection modes are those conventionally used by the ls(1) util-
ity. This is extended beyond the usage in the ISO POSIX-2 standard to sup-
port the "shared text" or "sticky" bit. It is intended that the conformance
document should not document anything beyond the existence of and support
of such a mode. Further extensions are expected to these bits, particu-
larly with overloading the set-user-ID and set-group-ID flags.
cpio Interchange Format
The reference to appropriate privilege in the cpio format refers to an
error on standard output; the ustar format does not make comparable state-
ments.
The model for this format was the historical System V cpio -c data inter-
change format. This model documents the portable version of the cpio format
and not the binary version. It has the flexibility to transfer data of any
type described within IEEE Std 1003.1-2001, yet is extensible to transfer
data types specific to extensions beyond IEEE Std 1003.1-2001 (for example,
contiguous files). Because it describes existing practice, there is no
question of maintaining upwards-compatibility.
cpio Header
There has been some concern that the size of the c_ino field of the header
is too small to handle those systems that have very large inode numbers.
However, the c_ino field in the header is used strictly as a hard-link res-
olution mechanism for archives. It is not necessarily the same value as the
inode number of the file in the location from which that file is extracted.
The name c_magic is based on historical usage.
cpio Filename
For most historical implementations of the cpio utility, {PATH_MAX} octets
can be used to describe the pathname without the addition of any other
header fields (the NUL character would be included in this count).
{PATH_MAX} is the minimum value for pathname size, documented as 256 bytes.
However, an implementation may use c_namesize to determine the exact length
of the pathname. With the current description of the header, this
pathname size can be as large as a number that is described in six octal
digits.
Two values are documented under the c_mode field values to provide for
extensibility for known file types:
0110 000
Reserved for contiguous files. The implementation may treat the rest
of the information for this archive like a regular file. If this
file type is undefined, the implementation may create the file as a
regular file.
This provides for extensibility of the cpio format while allowing for the
ability to read old archives. Files of an unknown type may be read as "reg-
ular files" on some implementations. On a system that does not support
extended file types, the pax utility should do the best it can with the
file and go on to the next.
FUTURE DIRECTIONS
None.
End of informative sections.
_________________________________________________________________
SEE ALSO
Shell Command Language, cp(1), ed(1), getopts(1), ls(1), printf(3), the
Base Definitions volume of IEEE Std 1003.1-2001, , the System
Interfaces volume of IEEE Std 1003.1-2001, chown(2), creat(2), mkdir(2),
mkfifo(2), stat(2), utime(2), write(2).
CHANGE HISTORY
First released in Issue 4.
Issue 5
A note is added to the APPLICATION USAGE indicating that the cpio and tar
formats can only support files up to 8 gigabytes in size.
Issue 6
The pax utility is aligned with the IEEE P1003.2b draft standard:
· Support has been added for symbolic links in the options and inter-
change formats.
· A new format has been devised, based on extensions to ustar.
· References to the "extended" tar and cpio formats derived from the
POSIX.1-1990 standard have been changed to remove the "extended"
adjective because this could cause confusion with the extended tar
header added in this revision. (All references to tar are actually
to ustar.)
The TZ entry is added to the ENVIRONMENT VARIABLES section.
IEEE PASC Interpretation 1003.2 #168 is applied, clarifying that mkdir(2)
and mkfifo(2) calls can ignore an [EEXIST] error when extracting an ar-
chive.
IEEE PASC Interpretation 1003.2 #180 is applied, clarifying how extracted
files are created when in read mode.
IEEE PASC Interpretation 1003.2 #181 is applied, clarifying the description
of the -t option.
IEEE PASC Interpretation 1003.2 #195 is applied.
IEEE PASC Interpretation 1003.2 #206 is applied, clarifying the handling of
links for the -H, -L, and -l options.
IEEE Std 1003.1-2001/Cor 1-2002, item XCU/TC1/D6/35 is applied, adding the
process ID of the pax process into certain fields. This change provides a
method for the implementation to ensure that different instances of pax
extracting a file named /a/b/foo will not collide when processing the
extended header information associated with foo.
IEEE Std 1003.1-2001/Cor 1-2002, item XCU/TC1/D6/36 is applied, changing -x
B to -x pax in the OPTIONS section.
IEEE Std 1003.1-2001/Cor 2-2004, item XCU/TC2/D6/20 is applied, updating
the SYNOPSIS to be consistent with the normative text.
IEEE Std 1003.1-2001/Cor 2-2004, item XCU/TC2/D6/21 is applied, updating
the DESCRIPTION to describe the behavior when files to be linked are sym-
bolic links and the system is not capable of making hard links to symbolic
links.
IEEE Std 1003.1-2001/Cor 2-2004, item XCU/TC2/D6/22 is applied, updating
the OPTIONS section to describe the behavior for how multiple options are
to be handled.
IEEE Std 1003.1-2001/Cor 2-2004, item XCU/TC2/D6/23 is applied, updating
the write option within the OPTIONS section.
IEEE Std 1003.1-2001/Cor 2-2004, item XCU/TC2/D6/24 is applied, adding a
paragraph into the OPTIONS section that states that specifying more than
one of the mutually-exclusive options (-H and -L) is not considered an
error and that the last option specified will determine the behavior of the
utility.
IEEE Std 1003.1-2001/Cor 2-2004, item XCU/TC2/D6/25 is applied, removing
the ctime paragraph within the EXTENDED DESCRIPTION. There is a contradic-
tion in the definition of the ctime keyword for the pax extended header, in
that the st_ctime member of the stat structure does not refer to a file
creation time. No field in the standard stat structure from
includes a file creation time.
IEEE Std 1003.1-2001/Cor 2-2004, item XCU/TC2/D6/26 is applied, making it
clear that typeflag 1 RB ( ustar Interchange Format) applies not only to
files that are hard-linked, but also to files that are aliased via sym-
links.
IEEE Std 1003.1-2001/Cor 2-2004, item XCU/TC2/D6/27 is applied, clarifying
the cpio c_nlink field.
End of quoted text from the POSIX.1-2001 standard.
OTHER OPTIONS
The following other options are implemented as extension to the POSIX stan-
dard. Note that some other non-POSIX options are mentioned in -help and
-xhelp output - these are also supported in spax(1) and are described in
the star(1) manual page.
-help Prints a summary of the most important options for spax(1) and
exits.
-do-statistics
Print statistic messages at the end of a spax(1) run.
-xhelp Prints a summary of the less important options for spax(1) and
exits.
-version
Prints the spax version number string and exists.
EXAMPLES
ENVIRONMENT
FILES
SEE ALSO
DIAGNOSTICS
NOTES
The Institute of Electrical and Electronics Engineers and The Open Group,
have given us permission to reprint portions of their documentation. In the
following statement, the phrase ``this text'' refers to portions of the
system documentation.
Portions of this text are reprinted and reproduced in electronic form in
the sfind manual, from IEEE Std 1003.1, 2004 Edition, Standard for Informa-
tion Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 6, Copyright (C) 2001-2004 by the Institute
of Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between these versions and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard is
the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html.
BUGS
AUTHOR
Joerg Schilling
Seestr. 110
D-13353 Berlin
Germany
Mail bugs and suggestions to:
schilling@fokus.fraunhofer.de or js@cs.tu-berlin.de or
joerg@schily.isdn.cs.tu-berlin.de
Joerg Schilling 13/04/16 SPAX(1L)