PAX(1) General Commands Manual PAX(1)
pax – read and write file archives and copy directory hierarchies
pax [-0cdjnOvz] [-E limit] [-f archive] [-G group] [-s replstr] [-T range]
[-U user] [pattern ...]
pax -r [-0cDdijknOuvYZz] [-E limit] [-f archive] [-G group] [-o options]
[-p string] [-s replstr] [-T range] [-U user] [pattern ...]
pax -w [-0adHijLOPtuvXz] [-B bytes] [-b blocksize] [-f archive] [-G group]
[-o options] [-s replstr] [-T range] [-U user] [-x format] [file ...]
pax -rw [-0DdHijkLlnOPtuvXYZ] [-G group] [-p string] [-s replstr]
[-T range] [-U user] [file ...] directory
pax will read, write, and list the members of an archive file and will copy
directory hierarchies. pax operation is independent of the specific
archive format and supports a wide variety of different archive formats. A
list of supported archive formats can be found under the description of the
The presence of the -r and the -w options specifies which of the following
functional modes pax will operate under: list, read, write, and copy.
<none> List. pax will write to standard output a table of contents of the
members of the archive file read from standard input, whose
pathnames match the specified pattern arguments. The table of
contents contains one filename per line and is written using single
-r Read. pax extracts the members of the archive file read from the
standard input, with pathnames matching the specified pattern
arguments. The archive format and blocking is automatically
determined on input. When an extracted file is a directory, the
entire file hierarchy rooted at that directory is extracted.
Extracted files are created either at absolute paths (those that
begin with a / character) or relative to the current file hierarchy
unless the -s option is used to remove leading slashes or add a
relative path prefix. Files being extracted to absolute paths may
overwrite files outside of the current working directory, so care
should be taken when extracting untrusted archives. The setting of
ownership, access and modification times, and file mode of the
extracted files are discussed in more detail under the -p option.
-w Write. pax writes an archive containing the file operands to
standard output using the specified archive format. When no file
operands are specified, a list of files to copy with one per line
is read from standard input. When a file operand is also a
directory, the entire file hierarchy rooted at that directory will
-rw Copy. pax copies the file operands to the destination directory.
When no file operands are specified, a list of files to copy with
one per line is read from the standard input. When a file operand
is also a directory the entire file hierarchy rooted at that
directory will be included. The effect of the copy is 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 (see the -l option below).
Warning: The destination directory must not be one of the file
operands or a member of a file hierarchy rooted at one of the file
operands. The result of a copy under these conditions is
While processing a damaged archive during a read or list operation, pax
will attempt to recover from media defects and will search through the
archive to locate and process the largest number of archive members
possible (see the -E option for more details on error handling).
The directory operand specifies a destination directory pathname. If the
directory operand does not exist, or it is not writable by the user, or it
is not of type directory, pax will exit with a non-zero exit status.
The pattern operand is used to select one or more pathnames of archive
members. Archive members are selected using the pattern matching notation
described by glob(3). When the pattern operand is not supplied, all
members of the archive will be selected. When a pattern matches a
directory, the entire file hierarchy rooted at that directory will be
selected. When a pattern operand does not select at least one archive
member, pax will write these pattern operands in a diagnostic message to
standard error and then exit with a non-zero exit status.
The file operand specifies the pathname of a file to be copied or archived.
When a file operand does not select at least one archive member, pax will
write these file operand pathnames in a diagnostic message to standard
error and then exit with a non-zero exit status.
The options are as follows:
-0 Use the NUL (‘\0’) character as a pathname terminator, instead of
newline (‘\n’). This applies only to the pathnames read from
standard input in the write and copy modes, and to the pathnames
written to standard output in list mode. This option is expected
to be used in concert with the -print0 function in find(1) or the
-0 flag in xargs(1).
-a Append the given file operands to the end of an archive that was
previously written. If an archive format is not specified with a
-x option, the format currently being used in the archive will be
selected. Any attempt to append to an archive in a format
different from the format already used in the archive will cause
pax to exit immediately with a non-zero exit status. The blocking
size used in the archive volume where writing starts will continue
to be used for the remainder of that archive volume.
Warning: Many storage devices are not able to support the
operations necessary to perform an append operation. Any attempt
to append to an archive stored on such a device may damage the
archive or have other unpredictable results. Tape drives in
particular are more likely to not support an append operation. An
archive stored in a regular file system file or on a disk device
will usually support an append operation.
Limit the number of bytes written to a single archive volume to
bytes. The bytes limit can end with ‘m’, ‘k’, or ‘b’ to specify
multiplication by 1048576 (1M), 1024 (1K) or 512, respectively. A
pair of bytes limits can be separated by ‘x’ to indicate a product.
Warning: Only use this option when writing an archive to a device
which supports an end of file read condition based on last (or
largest) write offset (such as a regular file or a tape drive).
The use of this option with a floppy or hard disk is not
When writing an archive, block the output at a positive decimal
integer number of bytes per write to the archive file. The
blocksize must be a multiple of 512 bytes with a maximum of 64512
bytes. Archive block sizes larger than 32256 bytes violate the
POSIX standard and will not be portable to all systems. A
blocksize can end with ‘k’ or ‘b’ to specify multiplication by 1024
(1K) or 512, respectively. A pair of blocksizes can be separated
by ‘x’ to indicate a product. A specific archive device may impose
additional restrictions on the size of blocking it will support.
When blocking is not specified, the default blocksize is dependent
on the specific archive format being used (see the -x option).
-c Match all file or archive members except those specified by the
pattern and file operands.
-D This option is the same as the -u option, except that the file
inode change time is checked instead of the file modification time.
The file inode change time can be used to select files whose inode
information (e.g., UID, GID, etc.) is newer than a copy of the file
in the destination directory.
-d Cause files of type directory being copied or archived, or archive
members of type directory being extracted, to match only the
directory file or archive member and not the file hierarchy rooted
at the directory.
Limit the number of consecutive read faults while trying to read a
flawed archive to limit. With a positive limit, pax will attempt
to recover from an archive read error and will continue processing
starting with the next file stored in the archive. A limit of 0
will cause pax to stop operation after the first read error is
detected on an archive volume. A limit of NONE will cause pax to
attempt to recover from read errors forever. The default limit is
a small positive number of retries.
Warning: Using this option with NONE should be used with extreme
caution as pax may get stuck in an infinite loop on a very badly
Specify archive as the pathname of the input or output archive,
overriding the default standard input (for list and read) or
standard output (for write). A single archive may span multiple
files and different archive devices. When required, pax will
prompt for the pathname of the file or device of the next volume in
Select a file based on its group name, or when starting with a #, a
numeric GID. A ‘\’ can be used to escape the #. Multiple -G
options may be supplied and checking stops with the first match.
-H Follow only command-line symbolic links while performing a physical
file system traversal.
-i Interactively rename files or archive members. For each archive
member matching a pattern operand or each file matching a file
operand, pax will prompt to /dev/tty giving the name of the file,
its file mode, and its modification time. pax will then read a
line from /dev/tty. If this line is blank, the file or archive
member is skipped. If this line consists of a single period, the
file or archive member is processed with no modification to its
name. Otherwise, its name is replaced with the contents of the
line. pax will immediately exit with a non-zero exit status if EOF
is encountered when reading a response or if /dev/tty cannot be
opened for reading and writing.
-j Use bzip2 to compress (decompress) the archive while writing
(reading). The bzip2 utility must be installed separately.
Incompatible with -a.
-k Do not overwrite existing files.
-L Follow all symbolic links to perform a logical file system
-l (The lowercase letter “ell”.) Link files. In the copy mode (-r
-w), hard links are made between the source and destination file
hierarchies whenever possible.
-n Select the first archive member that matches each pattern operand.
No more than one archive member is matched for each pattern. When
members of type directory are matched, the file hierarchy rooted at
that directory is also matched (unless -d is also specified).
-O Force the archive to be one volume. If a volume ends prematurely,
pax will not prompt for a new volume. This option can be useful
for automated tasks where error recovery cannot be performed by a
Information to modify the algorithm for extracting or writing
archive files which is specific to the archive format specified by
-x. In general, options take the form: name=value.
The following options are available for the old BSD tar format:
When writing archives, omit the storage of directories.
-P Do not follow symbolic links, perform a physical file system
traversal. This is the default mode.
Specify one or more file characteristic options (privileges). The
string option-argument is a string specifying file characteristics
to be retained or discarded on extraction. The string consists of
the specification characters a, e, m, o, and p. Multiple
characteristics can be concatenated within the same string and
multiple -p options can be specified. The meanings of the
specification characters are as follows:
a Do not preserve file access times. By default, file access
times are preserved whenever possible.
e “Preserve everything”, the user ID, group ID, file mode bits,
file access time, and file modification time. This is intended
to be used by root, someone with all the appropriate
privileges, in order to preserve all aspects of the files as
they are recorded in the archive. The e flag is the sum of the
o and p flags.
m Do not preserve file modification times. By default, file
modification times are preserved whenever possible.
o Preserve the user ID and group ID.
p “Preserve” the file mode bits. This is intended to be used by
a user with regular privileges who wants to preserve all
aspects of the file other than the ownership. The file times
are preserved by default, but two other flags are offered to
disable this and use the time of extraction instead.
In the preceding list, ‘preserve’ indicates that an attribute
stored in the archive is given to the extracted file, subject to
the permissions of the invoking process. Otherwise the attribute
of the extracted file is determined as part of the normal file
creation action. 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 will not set the S_ISUID (setuid) and
S_ISGID (setgid) bits of the file mode. If the preservation of any
of these items fails for any reason, pax will write a diagnostic
message to standard error. Failure to preserve these items will
affect the final exit status, but will not cause the extracted file
to be deleted. If the file characteristic letters in any of the
string option-arguments are duplicated or conflict with each other,
the one(s) given last will take precedence. For example, if -p eme
is specified, file modification times are still preserved.
-r Read an archive file from standard input and extract the specified
file operands. If any intermediate directories are needed in order
to extract an archive member, these directories will be created as
if mkdir(2) was called with the bitwise inclusive OR of S_IRWXU,
S_IRWXG, and S_IRWXO as the mode argument. When the selected
archive format supports the specification of linked files and these
files cannot be linked while the archive is being extracted, pax
will write a diagnostic message to standard error and exit with a
non-zero exit status at the completion of operation.
Modify the archive member names according to the substitution
expression replstr, using the syntax of the ed(1) utility regular
expressions. file or pattern arguments may be given to restrict
the list of archive members to those specified.
The format of these regular expressions is:
As in ed(1), old is a basic regular expression (see re_format(7))
and new can contain an ampersand (‘&’), ‘\n’ (where n is a digit)
back-references, or subexpression matching. The old string may
also contain newline characters. Any non-null character can be
used as a delimiter (‘/’ is shown here). Multiple -s expressions
can be specified. The expressions are applied in the order they
are specified on the command line, terminating with the first
The optional trailing g continues to apply the substitution
expression to the pathname substring, which starts with the first
character following the end of the last successful substitution.
The first unsuccessful substitution stops the operation of the g
option. The optional trailing p will cause the final result of a
successful substitution to be written to standard error in the
original-pathname >> new-pathname
File or archive member names that substitute to the empty string
are not selected and will be skipped.
Allow files to be selected based on a file modification or inode
change time falling within the specified time range. The range has
The dates specified by from_date to to_date are inclusive. If only
a from_date is supplied, all files with a modification or inode
change time equal to or younger are selected. If only a to_date is
supplied, all files with a modification or inode change time equal
to or older will be selected. When the from_date is equal to the
to_date, only files with a modification or inode change time of
exactly that time will be selected.
When pax is in the write or copy mode, the optional trailing field
[c] [m] can be used to determine which file time (inode change,
file modification or both) are used in the comparison. If neither
is specified, the default is to use file modification time only.
The m specifies the comparison of file modification time (the time
when the file was last written). The c specifies the comparison of
inode change time (the time when the file inode was last changed;
e.g., a change of owner, group, mode, etc). When c and m are both
specified, then the modification and inode change times are both
The inode change time comparison is useful in selecting files whose
attributes were recently changed or selecting files which were
recently created and had their modification time reset to an older
time (as what happens when a file is extracted from an archive and
the modification time is preserved). Time comparisons using both
file times is useful when pax is used to create a time based
incremental archive (only files that were changed during a
specified time range will be archived).
A time range is made up of six different fields and each field must
contain two digits. The format is:
Where cc is the first two digits of the year (the century), yy is
the last two digits of the year, the first mm is the month (from 01
to 12), dd is the day of the month (from 01 to 31), HH is the hour
of the day (from 00 to 23), MM is the minute (from 00 to 59), and
SS is the seconds (from 00 to 59). The minute field MM is
required, while the other fields are optional and must be added in
the following order: HH, dd, mm, yy, cc.
The SS field may be added independently of the other fields. Time
ranges are relative to the current time, so -T 1234/cm would select
all files with a modification or inode change time of 12:34 PM
today or later. Multiple -T time range can be supplied and
checking stops with the first match.
-t Reset the access times of any file or directory read or accessed by
pax to be the same as they were before being read or accessed by
Select a file based on its user name, or when starting with a #, a
numeric UID. A ‘\’ can be used to escape the #. Multiple -U
options may be supplied and checking stops with the first match.
-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. During read, an archive member with the same name as a file
in the file system will be extracted if the archive member is newer
than the file. During write, a file system member with the same
name as an archive member will be written to the archive if it is
newer than the archive member. During copy, the file in the
destination hierarchy is 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 During a list operation, produce a verbose table of contents using
the format of the ls(1) utility with the -l option. For pathnames
representing a hard link to a previous member of the archive, the
output has the format:
ls -l listing == link-name
For pathnames representing a symbolic link, the output has the
ls -l listing => link-name
Where ls -l listing is the output format specified by the ls(1)
utility when used with the -l option. Otherwise for all the other
operational modes (read, write, and copy), pathnames are written
and flushed to standard error without a trailing newline as soon as
processing begins on that file or archive member. The trailing
newline is not buffered and is written only after the file has been
read or written.
-w Write files to the standard output in the specified archive format.
When no file operands are specified, standard input is read for a
list of pathnames with one per line without any leading or trailing
-X When traversing the file hierarchy specified by a pathname, do not
descend into directories that have a different device ID. See the
st_dev field as described in stat(2) for more information about
Specify the output archive format, with the default format being
ustar. pax currently supports the following formats:
bcpio The old binary cpio format. The default blocksize for
this format is 5120 bytes. This format is not very
portable and should not be used when other formats are
available. Inode and device information about a file
(used for detecting file hard links by this format), which
may be truncated by this format, is detected by pax and is
cpio The extended cpio interchange format specified in the IEEE
Std 1003.2 (“POSIX.2”) standard. The default blocksize
for this format is 5120 bytes. Inode and device
information about a file (used for detecting file hard
links by this format), which may be truncated by this
format, is detected by pax and is repaired.
sv4cpio The System V release 4 cpio. The default blocksize for
this format is 5120 bytes. Inode and device information
about a file (used for detecting file hard links by this
format), which may be truncated by this format, is
detected by pax and is repaired.
sv4crc The System V release 4 cpio with file CRC checksums. The
default blocksize for this format is 5120 bytes. Inode
and device information about a file (used for detecting
file hard links by this format), which may be truncated by
this format, is detected by pax and is repaired.
tar The old BSD tar format as found in 4.3BSD. The default
blocksize for this format is 10240 bytes. Pathnames
stored by this format must be 100 characters or less in
length. Only regular files, hard links, soft links, and
directories will be archived (other file system types are
not supported). For backwards compatibility with even
older tar formats, a -o option can be used when writing an
archive to omit the storage of directories. This option
takes the form:
ustar The extended tar interchange format specified in the IEEE
Std 1003.2 (“POSIX.2”) standard. The default blocksize
for this format is 10240 bytes. Filenames stored by this
format must be 100 characters or less in length; the total
pathname must be 255 characters or less.
pax will detect and report any file that it is unable to store or
extract as the result of any specific archive format restrictions.
The individual archive formats may impose additional restrictions
on use. Typical archive format restrictions include (but are not
limited to): file pathname length, file size, link pathname length,
and the type of the file.
-Y This option is the same as the -D option, except that the inode
change time is checked using the pathname created after all the
file name modifications have completed.
-Z This option is the same as the -u option, except that the
modification time is checked using the pathname created after all
the file name modifications have completed.
-z Use gzip(1) to compress (decompress) the archive while writing
(reading). Incompatible with -a.
Normally pax ignores filenames or symbolic links that contain “..”
as a path component. With this option, files that contain “..” can
The options that operate on the names of files or archive members (-c, -i,
-j, -n, -s, -u, -v, -D, -G, -T, -U, -Y, and -Z) interact as follows.
When extracting files during a read operation, archive members are
‘selected’, based only on the user specified pattern operands as modified
by the -c, -n, -u, -D, -G, -T, -U options. Then any -s and -i options will
modify in that order, the names of these selected files. Then the -Y and
-Z options will be applied based on the final pathname. Finally, the -v
option will write the names resulting from these modifications.
When archiving files during a write operation, or copying files during a
copy operation, archive members are ‘selected’, based only on the user
specified pathnames as modified by the -n, -u, -D, -G, -T, and -U options
(the -D option only applies during a copy operation). Then any -s and -i
options will modify in that order, the names of these selected files. Then
during a copy operation the -Y and the -Z options will be applied based on
the final pathname. Finally, the -v option will write the names resulting
from these modifications.
When one or both of the -u or -D options are specified along with the -n
option, a file is not considered selected unless it is newer than the file
to which it is compared.
TMPDIR Path in which to store temporary files.
Copy the contents of the current directory to the device /dev/rst0:
$ pax -w -f /dev/rst0 .
Give the verbose table of contents for an archive stored in filename:
$ pax -v -f filename
This sequence of commands will copy the entire olddir directory hierarchy
$ mkdir newdir
$ cd olddir
$ pax -rw . ../newdir
Extract files from the archive a.pax. Files rooted in /usr are extracted
relative to the current working directory; all other files are extracted to
their unmodified path.
$ pax -r -s ',^/usr/,,' -f a.pax
This can be used to interactively select the files to copy from the current
directory to dest_dir:
$ pax -rw -i . dest_dir
Extract all files from the archive a.pax which are owned by root with group
bin and preserve all file permissions:
$ pax -r -pe -U root -G bin -f a.pax
Update (and list) only those files in the destination directory /backup
which are older (less recent inode change or file modification times) than
files with the same name found in the source file tree home:
$ pax -r -w -v -Y -Z home /backup
pax will exit with one of the following values:
0 All files were processed successfully.
1 An error occurred.
Whenever 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 is written to standard error and a non-zero exit status will be
returned, but processing will continue. In the case where pax cannot
create a link to a file, pax will not 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 a file the user
wanted. Additionally, the file modes of extracted files and directories
may have incorrect file bits, and the modification and access times may be
If the creation of an archive is prematurely terminated by a signal or
error, pax may have only partially created the archive, which may violate
the specific archive format specification.
If while doing a copy, pax detects a file is about to overwrite itself, the
file is not copied, a diagnostic message is written to standard error and
when pax completes it will exit with a non-zero exit status.
"Archiving with Pax", Dru Lavigne, ONLamp.com BSD DevCenter,
pax(1) manual page, http://heirloom.sourceforge.net/man/pax.1.html
The pax utility is compliant with the IEEE Std 1003.1-2004 (“POSIX.1”)
The flags [-0BDEGHjLOPTUYZz], the archive formats bcpio, sv4cpio, sv4crc,
tar, and the flawed archive handling during list and read operations are
extensions to that specification.
Keith Muller at the University of California, San Diego.
macOS 12.1 June 11, 2008 macOS 12.1