spax
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SPAX(1L) Schily´s USER COMMANDS SPAX(1L)
NAME
pax - portable archive interchange
SYNOPSIS
spax [ other options ] [-cdnv][-H|-L][-o options ][-f archive ][-s
replstr ] ... [ pattern ...]
spax [ other options ] -r[-cdiknuv][-H|-L][-f archive ][-o options ]
... [-p string ] ... [-s replstr] ... [ pattern ...]
spax [ other options ] -w[-dituvX][-H|-L][-b blocksize ][[-a][-f
archive ][-o options ] ... [-s replstr ] ... [-x format ][ file ...]
spax [ other options ] -r -w[-diklntuvX][-H|-L][-o options ]...[-p
string ]...[-s replstr ]...[ file ...] directory
DESCRIPTION
The manual page for spax is not yet ready. The following text is a
quotation from the POSIX.1-2001 standard.
The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition
Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.
------------------------------------------------------------------------
DESCRIPTION
The pax utility shall read, write, and write lists of the members
of archive 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 archive 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 directory 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 directory 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.
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.
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 formats 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 pattern 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 referencing a file of any other
file type which pax can normally archive is specified on the
command line, then 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.
-i Interactively rename files or archive members. For each
archive member matching a pattern operand or file matching a
file operand, a prompt shall be written to the file /dev/tty.
The prompt shall contain the name of the file or archive
member, but the format is otherwise 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 specified in conjunction with -H or -L, when a
symbolic link is encountered, 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
destination.
-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 specified 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 hierarchy 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 specified 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 circumstances described in pax Header Block.
The name shall be the contents of string, after the
following character substitutions 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 written 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 values 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
destination 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
written in the codeset and current locale of the
implementation.
The following mutually-exclusive values of the action
argument are supported:
bypass
In read or copy mode, pax shall bypass the file,
causing 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
filename 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,
translating the name, regardless of whether this
may overwrite 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) restrictions, and shall be
suppressed if the -k option is also specified.
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
contents 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 specified, the format
strings shall be considered a single, concatenated
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-arguments, 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,
" <archive
the group name will be forced to a new value for all
files read from the archive.
The precedence of -o keywords over various fields in the
archive is described in pax Extended Header Keyword
Precedence.
-p string
Specify one or more file characteristic options (privileges).
The string option-argument shall be a string specifying file
characteristics to be retained or discarded on extraction.
The string shall consist of the specification characters a ,
e, m, o, and p. Other implementation-defined characters can
be included. Multiple characteristics can be concatenated
within the same string and multiple -p options can be
specified. The meaning of the specification characters are as
follows:
a Do not preserve file access times.
e Preserve the user ID, group ID, file mode bits (see the
Base Definitions volume of IEEE Std 1003.1-2001, Section
3.168, File Mode Bits), access time, modification time,
and any other implementation-defined file
characteristics.
m Do not preserve file modification times.
o Preserve the user ID and group ID.
p Preserve the file mode bits. Other
implementation-defined file mode attributes may be
preserved.
In the preceding list, "preserve" indicates that an attribute
stored in the archive shall be given to the extracted file,
subject to the permissions of the invoking process. The
access and modification times of the file shall be preserved
unless otherwise specified with the -p option or not stored
in the archive. All attributes that are not preserved shall
be determined as part of the normal file creation action (see
File Read, Write, and Creation).
If neither the e nor the o specification character is
specified, or the user ID and group ID are not preserved for
any reason, pax shall not set the S_ISUID and S_ISGID bits of
the file mode.
If the preservation of any of these items fails for any
reason, pax shall write a diagnostic message to standard
error. Failure to preserve these items shall affect the final
exit status, but shall not cause the extracted file to be
deleted.
If file characteristic letters in any of the string
option-arguments are duplicated or conflict with each other,
the ones given last shall take precedence. For example, if -p
eme is specified, file modification times are preserved.
-s replstr
Modify file or archive member names named by pattern or file
operands according to the substitution expression replstr,
using the syntax of the ed utility. The concepts of "address"
and "line" are meaningless in the context of the pax utility,
and shall not be supplied. The format shall be:
-s /old/new/[gp]
where as in ed, old is a basic regular expression and new can
contain an ampersand, ’0 (where n is a digit)
backreferences, or subexpression matching. The old string
shall also be permitted to contain <newline>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 successful substitution. The
optional trailing ’g’ is as defined in the ed utility. The
optional trailing ’p’ shall cause successful substitutions 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 unspecified
whether this is accomplished by actual replacement in the
archive 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
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.
ustar
The tar interchange format; see the EXTENDED DESCRIPTION
section. 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 archive 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
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 <newline> 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, plus the
following exceptions:
6. The sequence ( keyword) can occur before a format conversion
specifier. The conversion argument is defined by the value of
keyword. The implementation shall support the following
keywords:
o 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.
o Any keyword defined for the extended header in pax
Extended Header.
o 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
Standard Output. If ( keyword) is omitted, the mode keyword
shall be used. For example, %.1M writes the single character
corresponding to the <entry type> 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 <space>.
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
concatenated 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", <value of keyword>, <contents of link>
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 pattern must be given in the name-generating notation of
the pattern matching notation in Pattern Matching Notation ,
including the filename 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 <blank>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 pattern 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 archive 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:
"%s0, <pathname>
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 following formats.
For pathnames representing hard links to previous members of the
archive:
"%s[Image]==[Image]%s0, <ls -l listing>, <linkname>
For all other pathnames:
"%s0, <ls -l listing>
where <ls -l listing> shall be the format specified by the ls
utility with the -l option. When writing pathnames in this format,
it is unspecified what is written for fields for which the
underlying archive format does not have the correct information,
although the correct number of <blank>-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 pathnames it processes to the standard error output using the
following format:
"%s0, <pathname>
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 <newline>, 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 format:
"%s[Image]>>[Image]%s0, <original pathname>, <new pathname>
In all operating modes of pax, optional messages of unspecified
format concerning 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
unspecified 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 codeset 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
associated 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, presumably because it has no need
for extended attributes.
[Image]
Figure: pax Format Archive Example
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 archive (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 subsequent 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 standard, 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=%s0, <length>, <keyword>, <value>
The extended header records shall be encoded according to the
ISO/IEC 10646-1:2000 standard (UTF-8). The <length> field,
<blank>, equals sign, and <newline> shown shall be limited to the
portable character set, as encoded in UTF-8. The <keyword> and
<value> fields can be any UTF-8 characters. The <length> field
shall be the decimal length of the extended header record in
octets, including the trailing <newline>.
The <keyword> 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 following 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() function. The access time
shall be restored if the process has the appropriate
privilege required to do so. The format of the <value> shall
be as described in pax Extended Header File Times.
charset
The name of the character set used to encode the data in the
following 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.
<value> Formal Standard
ISO-IR[Image]646[Image]1990 ISO/IEC 646:1990
ISO-IR[Image]8859[Image]1[Image]1998 ISO/IEC
8859-1:1998
ISO-IR[Image]8859[Image]2[Image]1999 ISO/IEC
8859-2:1999
ISO-IR[Image]8859[Image]3[Image]1999 ISO/IEC
8859-3:1999
ISO-IR[Image]8859[Image]4[Image]1998 ISO/IEC
8859-4:1998
ISO-IR[Image]8859[Image]5[Image]1999 ISO/IEC
8859-5:1999
ISO-IR[Image]8859[Image]6[Image]1999 ISO/IEC
8859-6:1999
ISO-IR[Image]8859[Image]7[Image]1987 ISO/IEC
8859-7:1987
ISO-IR[Image]8859[Image]8[Image]1999 ISO/IEC
8859-8:1999
ISO-IR[Image]8859[Image]9[Image]1999 ISO/IEC
8859-9:1999
ISO-IR[Image]8859[Image]10[Image]1998 ISO/IEC
8859-10:1998
ISO-IR[Image]8859[Image]13[Image]1998 ISO/IEC
8859-13:1998
ISO-IR[Image]8859[Image]14[Image]1998 ISO/IEC
8859-14:1998
ISO-IR[Image]8859[Image]15[Image]1999 ISO/IEC
8859-15:1999
ISO-IR[Image]10646[Image]2000 ISO/IEC
10646:2000
ISO-IR[Image]10646[Image]2000[Image]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 <value> 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 appropriate 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 represented 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() 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 <value> 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
standardization.
security.any
The keywords prefixed by "security." are reserved for future
standardization.
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 override 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 override 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 character 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
implementation-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 <value> 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
<value>s; all characters within the <value> 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 <value>. 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 <value>. 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 otherwise shall generate only enough digits so
that the same time shall be recovered if the file is extracted on
a system whose underlying implementation 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 transportable 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 archive 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 logical records may be written with a single operation
equivalent to the write() 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 contain undefined data.
The header logical record shall be structured as shown in the
following table. 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 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 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 terminated by one or more <space> 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 character), 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 1003.1-2001 Bit Description
Value
04000 S_ISUID Set UID on execution.
02000 S_ISGID Set GID on execution.
01000 <reserved> 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 privilege 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 implementation 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 following 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() 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 ( ’ ’ ) should be recognized
as meaning a regular file when extracting files from the
archive. Archives written with this version of the archive
file format create regular files with a typeflag 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-character 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
respectively. 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
allocation 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 support 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
associated 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
implementations. 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 numbers 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 necessary).
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
information shall be in the order indicated and described by the
following table; see also the <cpio.h> 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 written. 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 determined in an unspecified manner.
c_mode
Contains the file type and access permissions as defined in
the following 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 040000 Directory
C_ISFIFO 010000 FIFO
C_ISREG 0100000 Regular file
C_ISLNK 0120000 Symbolic link
C_ISBLK 060000 Block special file
C_ISCHR 020000 Character special file
C_ISSOCK 0140000 Socket
C_ISCTG 0110000 Reserved
Directories, FIFOs, symbolic links, and regular files shall
be supported 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 cannot 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 create 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 produces 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 format-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 unspecified 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 create 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 archive. 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 additional 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 consistent 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
commonly used:
-p e
‘‘Preserve everything". This would be used by the historical
superuser, 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 extraction.
The one pathname per line format of standard input precludes
pathnames containing <newline>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 archive 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 density (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%(size)D28.7’ -o listopt=’(name)s28(atime)T28T’
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 utilities.
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 permissions on extracted
files. Second, it is needlessly limiting, in that superusers
cannot extract files and own them as superuser unless the archive
was created by the superuser. (It should be noted that restoration
of ownerships and permissions for the superuser, by default, is
historical practice 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 privilege" 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() 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 specified 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 capability 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 example, there are restrictions on the length of
pathnames stored in the archive. 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 (215-512 bytes) is the
largest multiple of 512 bytes that fits into a signed 16-bit tape
controller 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 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 special 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 proposals had three
effects; the first was to cause special characters in patterns 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 matching a specified pattern. Only the second
behavior is retained by this volume 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 ability to make
pattern matching characters act as normal characters is useful for
parts of pax other than file extraction. Third, a finer degree of
control over the special characters is useful because users may
wish to normalize 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 utility. Both
methods are historical practice: cp provides a simpler, more
intuitive interface, while pax offers a finer granularity of
control. Each provides additional functionality to the other; in
particular, pax maintains the hard-link structure of the hierarchy
while cp 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 identical;
there seemed insufficient gain to applications to balance the
difficulty 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
implementations provide informative messages to the user on
standard error whenever the archive file is changed.
The -d option (do not create intermediate directories not listed
in the archive) 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 specification. 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 behavior of cpio.
Because the -i option uses /dev/tty, utilities without a
controlling terminal 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 character set were different from the source, the
filenames might be transformed into names matching existing files)
and also was made more general to protect files transferred
between file systems with different {NAME_MAX} values (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
granularity 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 certainly 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 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 specification.
The T conversion specifier allows time fields to be displayed in
any of the date formats. Unlike the ls 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, 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.
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 subsecond granularity
The following were not goals for this format because these are
better handled 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
developing 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 permissions of 600 or 700 are suggested.
The ustar typeflag field was used to accommodate the additional
functionality 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 typeflag, 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 standard 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
<value>s represent names of officially registered character sets
in the format required by the ISO 2375:1985 standard.
The normal comma or <blank>-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 extensions. 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 <length> 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 characters. 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 multiple 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
omitted 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 forward as much as possible. In particular,
attributes such as "high performance file" might be broadly but
not universally granted while set-user-ID or chown() 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
standard.
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 restoration is not needed,
this can be a significant burden. The archive is structured 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 contain 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
implementations needing more than the eleven octal digits allowed
by the ustar format. 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 completeness,
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 archive 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