PAX(1P) POSIX Programmer's Manual PAX(1P)
PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the correspond-
ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
NAME
pax - portable archive interchange
SYNOPSIS
pax [-cdnv][-H|-L][-f archive][-s replstr]...[pattern...]
pax -r[-cdiknuv][-H|-L][-f archive][-o options]...[-p string]...
[-s replstr]...[pattern...]
pax -w[-dituvX][-H|-L][-b blocksize][[-a][-f archive][-o options]...
[-s replstr]...[-x format][file...]
pax -r -w[-diklntuvX][-H|-L][-p string]...[-s replstr]...
[file...] directory
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 for-
mat 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. 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 out-
put ( 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 ar-
chive 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 pat-
tern (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 con-
sist 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 charac-
ter, 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 prece-
dence and the earlier shall be silently ignored. The following keyword values of options shall be supported for the file formats as indi-
cated:
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 pro-
duces 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.
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, equiva-
lent to the result of the dirname util-
ity 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 val-
ues, 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 or truncating 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, ctime, 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 exam-
ple, 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 charac-
teristics 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 pre-
serve 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, '
' (where n is a digit) backreferences, or subexpres-
sion 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 util-
ity. The optional trailing 'p' shall cause successful substitutions to be written to standard error. File or archive member names that sub-
stitute 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 hier-
archy 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 ar-
chive 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 ar-
chive 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 ar-
chive 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()).
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 modifica-
tions.
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 com-
pared.
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 Def-
initions 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:
* Any of the Field Name entries in ustar Header Block and Octet-Oriented cpio Archive Entry . The implementation may support the
cpio keywords without the leading c_ in addition to the form required by Values for cpio c_mode Field .
* Any keyword defined for the extended header in pax Extended Header .
* Any keyword provided as an implementation-defined extension within the extended header defined in pax Extended Header .
For example, the sequence "%(charset)s" is the string value of the name of the character set in the extended header.
The result of the keyword conversion argument shall be the value from the applicable header field or extended header, without any trailing
NULs.
All keyword values used as conversion arguments shall be translated from the UTF-8 encoding to the character set appropriate for the local
file system, user database, and so on, as applicable.
7. An additional conversion specifier character, T, shall be used to specify time formats. The T conversion specifier character can be
preceded by the sequence ( keyword= subformat), where subformat is a date format as defined by date operands. The default keyword
shall be mtime and the default subformat shall be:
%b %e %H:%M %Y
8. An additional conversion specifier character, M, shall be used to specify the file mode string as defined in ls 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 %(key-
word)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 sym-
bolic 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 path-
names, 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
Determine the location of message catalogs for the processing of LC_MESSAGES .
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 unspeci-
fied 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:
"%s
", <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 == %s
", <ls -l listing>, <linkname>
For all other pathnames:
"%s
", <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 follow-
ing format:
"%s
", <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 fol-
lowing format:
"%s >> %s
", <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), modifi-
cation 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.
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 type-
flag 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 ar-
chive.
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 fol-
lowing header block(s), as indicated in the following list of keywords.
An extended header shall consist of one or more records, each constructed as follows:
"%d %s=%s
", <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 con-
sisting 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 646 1990 ISO/IEC 646:1990
ISO-IR 8859 1 1998 ISO/IEC 8859-1:1998
ISO-IR 8859 2 1999 ISO/IEC 8859-2:1999
ISO-IR 8859 3 1999 ISO/IEC 8859-3:1999
ISO-IR 8859 4 1998 ISO/IEC 8859-4:1998
ISO-IR 8859 5 1999 ISO/IEC 8859-5:1999
ISO-IR 8859 6 1999 ISO/IEC 8859-6:1999
ISO-IR 8859 7 1987 ISO/IEC 8859-7:1987
ISO-IR 8859 8 1999 ISO/IEC 8859-8:1999
ISO-IR 8859 9 1999 ISO/IEC 8859-9:1999
ISO-IR 8859 10 1998 ISO/IEC 8859-10:1998
ISO-IR 8859 13 1998 ISO/IEC 8859-13:1998
ISO-IR 8859 14 1998 ISO/IEC 8859-14:1998
ISO-IR 8859 15 1999 ISO/IEC 8859-15:1999
ISO-IR 10646 2000 ISO/IEC 10646:2000
ISO-IR 10646 2000 UTF-8 ISO/IEC 10646, UTF-8 encoding
BINARY None.
The encoding is included in an extended header for information only; when pax is used as described in IEEE Std 1003.1-2001, it shall not
translate the file data into any other encoding. The BINARY entry indicates unencoded binary data.
When used in write or copy mode, it is implementation-defined whether pax includes a charset extended header record for a file.
comment
A series of characters used as a comment. All characters in the <value> field shall be ignored by pax.
ctime The file creation time for the following file(s), equivalent to the value of the st_ctime member of the stat structure for a file,
as described by the stat() function. The creation 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 .
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 implemen-
tation-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 type-
flag 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 porta-
ble 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 modifi-
cation 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 trans-
late 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 charac-
ter 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 Value IEEE Std 1003.1-2001 Bit Description
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, ini-
tialized 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 ( '