pax - Online in the Cloud

PROGRAM:

NAME

pax — read and write file archives and copy directory hierarchies

SYNOPSIS

pax [-0cdJjnOvz] [-E limit] [-f archive] [-G group] [-s replstr] [-T range] [-U user]
[pattern ...]
pax -r [-0cDdiJjknOuvYZz] [-E limit] [-f archive] [-G group] [-M flag] [-o options]
[-p string] [-s replstr] [-T range] [-U user] [pattern ...]
pax -w [-0adHiJjLOPtuvXz] [-B bytes] [-b blocksize] [-f archive] [-G group] [-M flag]
[-o options] [-s replstr] [-T range] [-U user] [-x format] [file ...]
pax -rw [-0DdHiJjkLlnOPtuvXYZ] [-G group] [-p string] [-s replstr] [-T range] [-U user]
[file ...] directory

DESCRIPTION

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 -x option.

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 line buffering.

-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. 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. 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 be included.

-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 unpredictable.

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.

-B bytes
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 recommended.

-b blocksize
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.

-E limit
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 flawed archive.

-f archive
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 the
archive.

-G group
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 the xz utility to compress (decompress) the archive while writing (reading).
Incompatible with -a.

-j Use the bzip2 utility to compress (decompress) the archive while writing (reading).
Incompatible with -a.

-k Do not overwrite existing files.

-L Follow all symbolic links to perform a logical file system traversal.

-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.

-M flag
Configure the archive normaliser. flag is either a numeric value compatible to
strtonum(3) which is directly stored in the flags word, or one of the following
values, optionally prefixed with “no-” to turn them off:

inodes 0x0001: Serialise inodes, zero device info.
(cpio, sv4cpio, sv4crc)
links 0x0002: Store content of hard links only once.
(cpio, sv4cpio, sv4crc)
mtime 0x0004: Zero out the file modification time.
(ar, cpio, sv4cpio, sv4crc, ustar)
uidgid 0x0008: Set owner to 0:0 (root:wheel).
(ar, cpio, sv4cpio, sv4crc, ustar)
verb 0x0010: Debug this option.
debug 0x0020: Debug file header storage.
lncp 0x0040: Extract hard links by copy if link fails.
numid 0x0080: Use only numeric uid and gid values.
(ustar)
gslash 0x0100: Append a slash after directory names.
(ustar)
set 0x0003: Keep ownership and mtime intact.
dist 0x008B: Clean everything except mtime.
norm 0x008F: Clean everything.
root 0x0089: Clean owner and device information.

When creating an archive and verbosely listing output, these normalisation
operations are not reflected in the output, because they are made only after the
output has been shown.

This option is only implemented for the ar, cpio, sv4cpio, sv4crc, and ustar file
format writing routines.

TODO: The pax frontend should be using the -o option for handling this feature
instead.

-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 human.

-o options
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:

nodir
write_opt=nodir
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.

-p string
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.

-s replstr
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:

/old/new/[gp]

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 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 format:

original-pathname >> new-pathname

File or archive member names that substitute to the empty string are not selected
and will be skipped.

-T range
Allow files to be selected based on a file modification or inode change time falling
within the specified time range. The range has the format:

[from_date][,to_date][/[c][m]]

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 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:

[[[[[cc]yy]mm]dd]HH]MM[.SS]

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 pax.

-U user
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 format:

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 <blanks>.

-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 device IDs.

-x format
Specify the output archive format, with the default format being ustar. pax
currently supports the following formats:

ar The Unix Archiver library format. This format matches APT repositories and
the BSD ar(1) specification, not GNU binutils (which can however read them)
or SYSV systems. See ar(5) on some operating systems for more information.

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 repaired.

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:

-o write_opt=nodir

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 256 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 the gzip(1) utility to compress (decompress) the archive while writing
(reading). Incompatible with -a.

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.

ENVIRONMENT

TMPDIR Path in which to store temporary files.

EXIT STATUS

The pax utility exits with one of the following values:

0 All files were processed successfully.
1 An error occurred.

EXAMPLES

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 to newdir:

$ 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

DIAGNOSTICS

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, unless -M lncp is given, 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 wrong.

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.

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