PAX(1) BSD General Commands Manual PAX(1)NAMEpax — read and write file archives and copy directory hierarchies
SYNOPSISpax [-cdnvz] [-f archive] [-s replstr] ... [-U user] ... [-G group] ...
[-T [from_date] [,to_date]] ... [pattern ...]
pax-r [-cdiknuvzDYZ] [-f archive] [-o options] ... [-p string] ...
[-s replstr] ... [-E limit] [-U user] ... [-G group] ... [-T
[from_date] [,to_date]] ... [pattern ...]
pax-w [-dituvzHLPX] [-b blocksize] [[-a] [-f archive]] [-x format]
[-s replstr] ... [-o options] ... [-U user] ... [-G group] ...
[-B bytes] [-T [from_date] [,to_date] [/[c][m]]] ... [file ...]
pax-r -w [-diklntuvDHLPXYZ] [-p string] ... [-s replstr] ... [-U user]
... [-G group] ... [-T [from_date] [,to_date] [/[c][m]]] ...
[file ...] directory
The pax utility will read, write, and list the members of an archive
file, and will copy directory hierarchies. These operations are indepen‐
dent of the specific archive format, and support a wide variety of dif‐
ferent archive formats. A list of supported archive formats can be found
under the description of the -x option.
The presence of the -r and the -w options specifies which of the follow‐
ing functional modes pax will operate under: list, read, write, and copy.
<none> List. Write to standard output a table of contents of the mem‐
bers of the archive file read from standard input, whose path‐
names match the specified patterns. The table of contents con‐
tains one filename per line and is written using single line
-r Read. Extract the members of the archive file read from the
standard input, with pathnames matching the specified patterns.
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. All extracted
files are created relative to the current file hierarchy. 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. Write 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 be
-r -w Copy. Copy 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 direc‐
tory will be included. The effect of the copy is as if the
copied files were written to an archive file and then subse‐
quently 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 pos‐
sible (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 nota‐
tion described by fnmatch(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 mem‐
ber, pax will write these file operand pathnames in a diagnostic message
to standard error and then exit with a non-zero exit status.
The following options are supported:
-r Read an archive file from standard input and extract the specified
files. 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 ar‐
chive 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.
-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
-a Append files 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 vol‐
ume 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 opera‐
tions 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 sup‐
port an append operation.
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. A blocksize larger than 32256 bytes violates 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 indi‐
cate a product. A specific archive device may impose additional
restrictions on the size of blocking it will support. When block‐
ing 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 Cause files of type directory being copied or archived, or archive
members of type directory being extracted, to match only the direc‐
tory file or archive member and not the file hierarchy rooted at
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
-i Interactively rename files or archive members. For each archive
member matching a pattern operand or each file matching a file op‐
erand, pax will prompt to /dev/tty giving the name of the file, its
file mode and its modification time. The pax utility will then
read a line from /dev/tty. If this line is blank, the file or ar‐
chive 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. The pax utility 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.
-k Do not overwrite existing files.
-l Link files. (The letter ell). In the copy mode (-r -w), hard
links are made between the source and destination file hierarchies
-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).
Information to modify the algorithm for extracting or writing ar‐
chive files which is specific to the archive format specified by
-x. In general, options take the form: name=value
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 charac‐
teristics 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. 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 privi‐
leges, 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 mod‐
ification times are preserved whenever possible.
o Preserve the user ID and group ID.
p ‘Preserve’ the file mode bits. This 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 pre‐
served 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 cre‐
ation 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
is specified, file modification times are still preserved.
Modify the file or archive member names specified by the pattern or
file operands according to the substitution expression replstr,
using the syntax of the ed(1) utility regular expressions. The
format of these regular expressions are:
As in ed(1), old is a basic regular expression and new can contain
an ampersand (&), \n (where n is a digit) back-references, or sub‐
expression 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 com‐
mand line, terminating with the first successful substitution. 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 following for‐
<original pathname> >> <new pathname>
File or archive member names that substitute to the empty string
are not selected and will be skipped.
-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
-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 desti‐
nation 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 for‐
<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.
Specify the output archive format, with the default format being
ustar. The pax utility currently supports the following formats:
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 informa‐
tion 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.
bcpio The old binary cpio format. The default blocksize for
this format is 5120 bytes. This format is not very porta‐
ble and should not be used when other formats are avail‐
able. 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
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. Pathnames stored by this
format must be 255 characters or less in length. The
directory part may be at most 155 characters and each path
component must be less than 100 characters.
The pax utility 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.
-z Use gzip(1) to compress (decompress) the archive while writing
(reading). Incompatible with -a.
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 multi‐
plication 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 recom‐
-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.
Limit the number of consecutive read faults while trying to read a
flawed archives 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
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.
-L Follow all symbolic links to perform a logical file system traver‐
-P Do not follow symbolic links, perform a physical file system tra‐
versal. This is the default mode.
Allow files to be selected based on a file modification or inode
change time falling within a specified time range of from_date to
to_date (the dates are inclusive). If only a from_date is sup‐
plied, 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
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
compared. 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 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), the second 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.
The ss field may be added independently of the other fields. Time
ranges are relative to the current time, so
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.
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.
-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
-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 modifica‐
tion time is checked using the pathname created after all the file
name modifications have completed.
The options that operate on the names of files or archive members (-c,
-i, -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.
The pax utility will exit with one of the following values:
0 All files were processed successfully.
1 An error occurred.
pax-w -f /dev/sa0 .
copies the contents of the current directory to the device /dev/sa0.
pax-v -f filename
gives the verbose table of contents for an archive stored in filename.
The following commands:
pax-rw . /tmp/to
will copy the entire /tmp/from directory hierarchy to /tmp/to.
pax-r -s ',^//*usr//*,,' -f a.pax
reads the archive a.pax, with all files rooted in ``/usr'' into the ar‐
chive extracted relative to the current directory.
pax-rw -i . dest_dir
can be used to interactively select the files to copy from the current
directory to dest_dir.
pax-r -pe -U root -G bin -f a.pax
will extract all files from the archive a.pax which are owned by root
with group bin and will preserve all file permissions.
pax-r -w -v -Y -Z home /backup
will 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.
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
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.
SEE ALSOcpio(1), tar(1)STANDARDS
The pax utility is a superset of the IEEE Std 1003.2 (“POSIX.2”) stan‐
dard. The options -z, -B, -D, -E, -G, -H, -L, -P, -T, -U, -Y, -Z, the
archive formats bcpio, sv4cpio, sv4crc, tar, and the flawed archive han‐
dling during list and read operations are extensions to the POSIX stan‐
The pax utility appeared in 4.4BSD.
Keith Muller at the University of California, San Diego
The pax utility does not recognize multibyte characters.
BSD August 29, 2010 BSD