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TAR(1)                    BSD General Commands Manual                   TAR(1)

NAME
     tar — manipulate tape archives

SYNOPSIS
     tar [bundled-flags ⟨args⟩] [⟨file⟩ | ⟨pattern⟩ ...]
     tar {-c} [options] [files | directories]
     tar {-r | -u} -f archive-file [options] [files | directories]
     tar {-t | -x} [options] [patterns]

DESCRIPTION
     tar creates and manipulates streaming archive files.  This implementation
     can extract from tar, pax, cpio, zip, jar, ar, xar, rpm, 7-zip, and ISO
     9660 cdrom images and can create tar, pax, cpio, ar, zip, 7-zip, and shar
     archives.

     The first synopsis form shows a “bundled” option word.  This usage is
     provided for compatibility with historical implementations.  See COMPATI‐
     BILITY below for details.

     The other synopsis forms show the preferred usage.  The first option to
     tar is a mode indicator from the following list:
     -c      Create a new archive containing the specified items.  The long
             option form is --create.
     -r      Like -c, but new entries are appended to the archive.  Note that
             this only works on uncompressed archives stored in regular files.
             The -f option is required.  The long option form is --append.
     -t      List archive contents to stdout.  The long option form is --list.
     -u      Like -r, but new entries are added only if they have a modifica‐
             tion date newer than the corresponding entry in the archive.
             Note that this only works on uncompressed archives stored in reg‐
             ular files.  The -f option is required.  The long form is
             --update.
     -x      Extract to disk from the archive.  If a file with the same name
             appears more than once in the archive, each copy will be
             extracted, with later copies overwriting (replacing) earlier
             copies.  The long option form is --extract.

     In -c, -r, or -u mode, each specified file or directory is added to the
     archive in the order specified on the command line.  By default, the con‐
     tents of each directory are also archived.

     In extract or list mode, the entire command line is read and parsed
     before the archive is opened.  The pathnames or patterns on the command
     line indicate which items in the archive should be processed.  Patterns
     are shell-style globbing patterns as documented in tcsh(1).

OPTIONS
     Unless specifically stated otherwise, options are applicable in all oper‐
     ating modes.

     @archive
             (c and r mode only) The specified archive is opened and the
             entries in it will be appended to the current archive.  As a sim‐
             ple example,
                   tar -c -f - newfile @original.tar
             writes a new archive to standard output containing a file newfile
             and all of the entries from original.tar.  In contrast,
                   tar -c -f - newfile original.tar
             creates a new archive with only two entries.  Similarly,
                   tar -czf - --format pax @-
             reads an archive from standard input (whose format will be deter‐
             mined automatically) and converts it into a gzip-compressed pax-
             format archive on stdout.  In this way, tar can be used to con‐
             vert archives from one format to another.

     -a, --auto-compress
             (c mode only) Use the archive suffix to decide a set of the for‐
             mat and the compressions.  As a simple example,
                   tar -a -cf archive.tgz source.c source.h
             creates a new archive with restricted pax format and gzip com‐
             pression,
                   tar -a -cf archive.tar.bz2.uu source.c source.h
             creates a new archive with restricted pax format and bzip2 com‐
             pression and uuencode compression,
                   tar -a -cf archive.zip source.c source.h
             creates a new archive with zip format,
                   tar -a -jcf archive.tgz source.c source.h
             ignores the “-j” option, and creates a new archive with
             restricted pax format and gzip compression,
                   tar -a -jcf archive.xxx source.c source.h
             if it is unknown suffix or no suffix, creates a new archive with
             restricted pax format and bzip2 compression.

     -B, --read-full-blocks
             Ignored for compatibility with other tar(1) implementations.

     -b blocksize, --block-size blocksize
             Specify the block size, in 512-byte records, for tape drive I/O.
             As a rule, this argument is only needed when reading from or
             writing to tape drives, and usually not even then as the default
             block size of 20 records (10240 bytes) is very common.

     -C directory, --cd directory, --directory directory
             In c and r mode, this changes the directory before adding the
             following files.  In x mode, change directories after opening the
             archive but before extracting entries from the archive.

     --chroot
             (x mode only) chroot() to the current directory after processing
             any -C options and before extracting any files.

     --clear-nochange-fflags
             (x mode only) Before removing file system objects to replace
             them, clear platform-specific file flags that might prevent
             removal.

     --disable-copyfile
             Mac OS X specific.  Disable the use of copyfile(3).

     --exclude pattern
             Do not process files or directories that match the specified pat‐
             tern.  Note that exclusions take precedence over patterns or
             filenames specified on the command line.

     --format format
             (c, r, u mode only) Use the specified format for the created ar‐
             chive.  Supported formats include “cpio”, “pax”, “shar”, and
             “ustar”.  Other formats may also be supported; see
             libarchive-formats(5) for more information about currently-sup‐
             ported formats.  In r and u modes, when extending an existing ar‐
             chive, the format specified here must be compatible with the for‐
             mat of the existing archive on disk.

     -f file, --file file
             Read the archive from or write the archive to the specified file.
             The filename can be - for standard input or standard output.  The
             default varies by system; on FreeBSD, the default is /dev/sa0; on
             Linux, the default is /dev/st0.

     --gid id
             Use the provided group id number.  On extract, this overrides the
             group id in the archive; the group name in the archive will be
             ignored.  On create, this overrides the group id read from disk;
             if --gname is not also specified, the group name will be set to
             match the group id.

     --gname name
             Use the provided group name.  On extract, this overrides the
             group name in the archive; if the provided group name does not
             exist on the system, the group id (from the archive or from the
             --gid option) will be used instead.  On create, this sets the
             group name that will be stored in the archive; the name will not
             be verified against the system group database.

     -H      (c and r mode only) Symbolic links named on the command line will
             be followed; the target of the link will be archived, not the
             link itself.

     -h      (c and r mode only) Synonym for -L.

     -I      Synonym for -T.

     --help  Show usage.

     --hfsCompression
             (x mode only) Mac OS X specific(v10.6 or later). Compress
             extracted regular files with HFS+ compression.

     --ignore-zeros
             An alias of --options read_concatenated_archives for compatibil‐
             ity with GNU tar.

     --include pattern
             Process only files or directories that match the specified pat‐
             tern.  Note that exclusions specified with --exclude take prece‐
             dence over inclusions.  If no inclusions are explicitly speci‐
             fied, all entries are processed by default.  The --include option
             is especially useful when filtering archives.  For example, the
             command
                   tar -c -f new.tar --include='*foo*' @old.tgz
             creates a new archive new.tar containing only the entries from
             old.tgz containing the string ‘foo’.

     -J, --xz
             (c mode only) Compress the resulting archive with xz(1).  In
             extract or list modes, this option is ignored.  Note that, unlike
             other tar implementations, this implementation recognizes XZ com‐
             pression automatically when reading archives.

     -j, --bzip, --bzip2, --bunzip2
             (c mode only) Compress the resulting archive with bzip2(1).  In
             extract or list modes, this option is ignored.  Note that, unlike
             other tar implementations, this implementation recognizes bzip2
             compression automatically when reading archives.

     -k, --keep-old-files
             (x mode only) Do not overwrite existing files.  In particular, if
             a file appears more than once in an archive, later copies will
             not overwrite earlier copies.

     --keep-newer-files
             (x mode only) Do not overwrite existing files that are newer than
             the versions appearing in the archive being extracted.

     -L, --dereference
             (c and r mode only) All symbolic links will be followed.  Nor‐
             mally, symbolic links are archived as such.  With this option,
             the target of the link will be archived instead.

     -l, --check-links
             (c and r modes only) Issue a warning message unless all links to
             each file are archived.

     --lrzip
             (c mode only) Compress the resulting archive with lrzip(1).  In
             extract or list modes, this option is ignored.

     --lz4   (c mode only) Compress the archive with lz4-compatible compres‐
             sion before writing it.  In input mode, this option is ignored;
             lz4 compression is recognized automatically on input.

     --lzma  (c mode only) Compress the resulting archive with the original
             LZMA algorithm.  Use of this option is discouraged and new ar‐
             chives should be created with --xz instead.  Note that, unlike
             other tar implementations, this implementation recognizes LZMA
             compression automatically when reading archives.

     --lzop  (c mode only) Compress the resulting archive with lzop(1).  In
             extract or list modes, this option is ignored.

     -m, --modification-time
             (x mode only) Do not extract modification time.  By default, the
             modification time is set to the time stored in the archive.

     -n, --norecurse, --no-recursion
             (c, r, u modes only) Do not recursively archive the contents of
             directories.

     --newer date
             (c, r, u modes only) Only include files and directories newer
             than the specified date.  This compares ctime entries.

     --newer-mtime date
             (c, r, u modes only) Like --newer, except it compares mtime
             entries instead of ctime entries.

     --newer-than file
             (c, r, u modes only) Only include files and directories newer
             than the specified file.  This compares ctime entries.

     --newer-mtime-than file
             (c, r, u modes only) Like --newer-than, except it compares mtime
             entries instead of ctime entries.

     --nodump
             (c and r modes only) Honor the nodump file flag by skipping this
             file.

     --nopreserveHFSCompression
             (x mode only) Mac OS X specific(v10.6 or later). Do not compress
             extracted regular files which were compressed with HFS+ compres‐
             sion before archived.  By default, compress the regular files
             again with HFS+ compression.

     --null  (use with -I or -T) Filenames or patterns are separated by null
             characters, not by newlines.  This is often used to read file‐
             names output by the -print0 option to find(1).

     --no-same-owner
             (x mode only) Do not extract owner and group IDs.  This is the
             reverse of --same-owner and the default behavior if tar is run as
             non-root.

     --no-same-permissions
             (x mode only) Do not extract full permissions (SGID, SUID, sticky
             bit, ACLs, extended attributes or extended file flags).  This is
             the reverse of -p and the default behavior if tar is run as non-
             root.

     --numeric-owner
             This is equivalent to --uname "" --gname "".  On extract, it
             causes user and group names in the archive to be ignored in favor
             of the numeric user and group ids.  On create, it causes user and
             group names to not be stored in the archive.

     -O, --to-stdout
             (x, t modes only) In extract (-x) mode, files will be written to
             standard out rather than being extracted to disk.  In list (-t)
             mode, the file listing will be written to stderr rather than the
             usual stdout.

     -o      (x mode) Use the user and group of the user running the program
             rather than those specified in the archive.  Note that this has
             no significance unless -p is specified, and the program is being
             run by the root user.  In this case, the file modes and flags
             from the archive will be restored, but ACLs or owner information
             in the archive will be discarded.

     -o      (c, r, u mode) A synonym for --format ustar

     --older date
             (c, r, u modes only) Only include files and directories older
             than the specified date.  This compares ctime entries.

     --older-mtime date
             (c, r, u modes only) Like --older, except it compares mtime
             entries instead of ctime entries.

     --older-than file
             (c, r, u modes only) Only include files and directories older
             than the specified file.  This compares ctime entries.

     --older-mtime-than file
             (c, r, u modes only) Like --older-than, except it compares mtime
             entries instead of ctime entries.

     --one-file-system
             (c, r, and u modes) Do not cross mount points.

     --options options
             Select optional behaviors for particular modules.  The argument
             is a text string containing comma-separated keywords and values.
             These are passed to the modules that handle particular formats to
             control how those formats will behave.  Each option has one of
             the following forms:
             key=value
                     The key will be set to the specified value in every mod‐
                     ule that supports it.  Modules that do not support this
                     key will ignore it.
             key     The key will be enabled in every module that supports it.
                     This is equivalent to key=1.
             !key    The key will be disabled in every module that supports
                     it.
             module:key=value, module:key, module:!key
                     As above, but the corresponding key and value will be
                     provided only to modules whose name matches module.
             The currently supported modules and keys are:
             iso9660:joliet
                     Support Joliet extensions.  This is enabled by default,
                     use !joliet or iso9660:!joliet to disable.
             iso9660:rockridge
                     Support Rock Ridge extensions.  This is enabled by
                     default, use !rockridge or iso9660:!rockridge to disable.
             gzip:compression-level
                     A decimal integer from 1 to 9 specifying the gzip com‐
                     pression level.
             gzip:timestamp
                     Store timestamp. This is enabled by default, use
                     !timestamp or gzip:!timestamp to disable.
             lrzip:compression=type
                     Use type as compression method.  Supported values are
                     bzip2, gzip, lzo (ultra fast), and zpaq (best, extremely
                     slow).
             lrzip:compression-level
                     A decimal integer from 1 to 9 specifying the lrzip com‐
                     pression level.
             lz4:compression-level
                     A decimal integer from 1 to 9 specifying the lzop com‐
                     pression level.
             lz4:stream-checksum
                     Enable stream checksum. This is by default, use
                     lz4:!stream-checksum to disable.
             lz4:block-checksum
                     Enable block checksum (Disabled by default).
             lz4:block-size
                     A decimal integer from 4 to 7 specifying the lz4 compres‐
                     sion block size (7 is set by default).
             lz4:block-dependence
                     Use the previous block of the block being compressed for
                     a compression dictionary to improve compression ratio.
             lzop:compression-level
                     A decimal integer from 1 to 9 specifying the lzop com‐
                     pression level.
             xz:compression-level
                     A decimal integer from 0 to 9 specifying the xz compres‐
                     sion level.
             mtree:keyword
                     The mtree writer module allows you to specify which mtree
                     keywords will be included in the output.  Supported key‐
                     words include: cksum, device, flags, gid, gname, indent,
                     link, md5, mode, nlink, rmd160, sha1, sha256, sha384,
                     sha512, size, time, uid, uname.  The default is equiva‐
                     lent to: “device, flags, gid, gname, link, mode, nlink,
                     size, time, type, uid, uname”.
             mtree:all
                     Enables all of the above keywords.  You can also use
                     mtree:!all to disable all keywords.
             mtree:use-set
                     Enable generation of /set lines in the output.
             mtree:indent
                     Produce human-readable output by indenting options and
                     splitting lines to fit into 80 columns.
             zip:compression=type
                     Use type as compression method.  Supported values are
                     store (uncompressed) and deflate (gzip algorithm).
             zip:encryption
                     Enable encryption using traditional zip encryption.
             zip:encryption=type
                     Use type as encryption type.  Supported values are
                     zipcrypt (traditional zip encryption), aes128 (WinZip
                     AES-128 encryption) and aes256 (WinZip AES-256 encryp‐
                     tion).
             read_concatenated_archives
                     Ignore zeroed blocks in the archive, which occurs when
                     multiple tar archives have been concatenated together.
                     Without this option, only the contents of the first con‐
                     catenated archive would be read.  This option is compara‐
                     ble to the -i, --ignore-zeros option of GNU tar.
             If a provided option is not supported by any module, that is a
             fatal error.

     -P, --absolute-paths
             Preserve pathnames.  By default, absolute pathnames (those that
             begin with a / character) have the leading slash removed both
             when creating archives and extracting from them.  Also, tar will
             refuse to extract archive entries whose pathnames contain .. or
             whose target directory would be altered by a symlink.  This
             option suppresses these behaviors.

     -p, --insecure, --preserve-permissions
             (x mode only) Preserve file permissions.  Attempt to restore the
             full permissions, including owner, file modes, file flags and
             ACLs, if available, for each item extracted from the archive.
             This is the default, if tar is being run by root and can be over‐
             ridden by also specifying --no-same-owner and
             --no-same-permissions.

     --passphrase passphrase
             The passphrase is used to extract or create an encrypted archive.
             Currently, zip is the only supported format that supports encryp‐
             tion.  You shouldn't use this option unless you realize how inse‐
             cure use of this option is.

     --posix
             (c, r, u mode only) Synonym for --format pax

     -q, --fast-read
             (x and t mode only) Extract or list only the first archive entry
             that matches each pattern or filename operand.  Exit as soon as
             each specified pattern or filename has been matched.  By default,
             the archive is always read to the very end, since there can be
             multiple entries with the same name and, by convention, later
             entries overwrite earlier entries.  This option is provided as a
             performance optimization.

     -S      (x mode only) Extract files as sparse files.  For every block on
             disk, check first if it contains only NULL bytes and seek over it
             otherwise.  This works similar to the conv=sparse option of dd.

     -s pattern
             Modify file or archive member names according to pattern.  The
             pattern has the format /old/new/[ghHprRsS] where old is a basic
             regular expression, new is the replacement string of the matched
             part, and the optional trailing letters modify how the replace‐
             ment is handled.  If old is not matched, the pattern is skipped.
             Within new, ~ is substituted with the match, \1 to \9 with the
             content of the corresponding captured group.  The optional trail‐
             ing g specifies that matching should continue after the matched
             part and stop on the first unmatched pattern.  The optional
             trailing s specifies that the pattern applies to the value of
             symbolic links.  The optional trailing p specifies that after a
             successful substitution the original path name and the new path
             name should be printed to standard error.  Optional trailing H,
             R, or S characters suppress substitutions for hardlink targets,
             regular filenames, or symlink targets, respectively.  Optional
             trailing h, r, or s characters enable substitutions for hardlink
             targets, regular filenames, or symlink targets, respectively.
             The default is hrs which applies substitutions to all names.  In
             particular, it is never necessary to specify h, r, or s.

     --same-owner
             (x mode only) Extract owner and group IDs.  This is the reverse
             of --no-same-owner and the default behavior if tar is run as
             root.

     --strip-components count
             Remove the specified number of leading path elements.  Pathnames
             with fewer elements will be silently skipped.  Note that the
             pathname is edited after checking inclusion/exclusion patterns
             but before security checks.

     -T filename, --files-from filename
             In x or t mode, tar will read the list of names to be extracted
             from filename.  In c mode, tar will read names to be archived
             from filename.  The special name “-C” on a line by itself will
             cause the current directory to be changed to the directory speci‐
             fied on the following line.  Names are terminated by newlines
             unless --null is specified.  Note that --null also disables the
             special handling of lines containing “-C”.  Note:      If you are
             generating lists of files using find(1), you probably want to use
             -n as well.

     --totals
             (c, r, u mode only) After archiving all files, print a summary to
             stderr.

     -U, --unlink, --unlink-first
             (x mode only) Unlink files before creating them.  This can be a
             minor performance optimization if most files already exist, but
             can make things slower if most files do not already exist.  This
             flag also causes tar to remove intervening directory symlinks
             instead of reporting an error.  See the SECURITY section below
             for more details.

     --uid id
             Use the provided user id number and ignore the user name from the
             archive.  On create, if --uname is not also specified, the user
             name will be set to match the user id.

     --uname name
             Use the provided user name.  On extract, this overrides the user
             name in the archive; if the provided user name does not exist on
             the system, it will be ignored and the user id (from the archive
             or from the --uid option) will be used instead.  On create, this
             sets the user name that will be stored in the archive; the name
             is not verified against the system user database.

     --use-compress-program program
             Pipe the input (in x or t mode) or the output (in c mode) through
             program instead of using the builtin compression support.

     -v, --verbose
             Produce verbose output.  In create and extract modes, tar will
             list each file name as it is read from or written to the archive.
             In list mode, tar will produce output similar to that of ls(1).
             An additional -v option will also provide ls-like details in cre‐
             ate and extract mode.

     --version
             Print version of tar and libarchive, and exit.

     -w, --confirmation, --interactive
             Ask for confirmation for every action.

     -X filename, --exclude-from filename
             Read a list of exclusion patterns from the specified file.  See
             --exclude for more information about the handling of exclusions.

     -y      (c mode only) Compress the resulting archive with bzip2(1).  In
             extract or list modes, this option is ignored.  Note that, unlike
             other tar implementations, this implementation recognizes bzip2
             compression automatically when reading archives.

     -Z, --compress, --uncompress
             (c mode only) Compress the resulting archive with compress(1).
             In extract or list modes, this option is ignored.  Note that,
             unlike other tar implementations, this implementation recognizes
             compress compression automatically when reading archives.

     -z, --gunzip, --gzip
             (c mode only) Compress the resulting archive with gzip(1).  In
             extract or list modes, this option is ignored.  Note that, unlike
             other tar implementations, this implementation recognizes gzip
             compression automatically when reading archives.

ENVIRONMENT
     The following environment variables affect the execution of tar:

     TAR_READER_OPTIONS
                The default options for format readers and compression read‐
                ers.  The --options option overrides this.

     TAR_WRITER_OPTIONS
                The default options for format writers and compression writ‐
                ers.  The --options option overrides this.

     LANG       The locale to use.  See environ(7) for more information.

     TAPE       The default device.  The -f option overrides this.  Please see
                the description of the -f option above for more details.

     TZ         The timezone to use when displaying dates.  See environ(7) for
                more information.

EXIT STATUS
     The tar utility exits 0 on success, and >0 if an error occurs.

EXAMPLES
     The following creates a new archive called file.tar.gz that contains two
     files source.c and source.h:
           tar -czf file.tar.gz source.c source.h

     To view a detailed table of contents for this archive:
           tar -tvf file.tar.gz

     To extract all entries from the archive on the default tape drive:
           tar -x

     To examine the contents of an ISO 9660 cdrom image:
           tar -tf image.iso

     To move file hierarchies, invoke tar as
           tar -cf - -C srcdir . | tar -xpf - -C destdir
     or more traditionally
           cd srcdir ; tar -cf - . | (cd destdir ; tar -xpf -)

     In create mode, the list of files and directories to be archived can also
     include directory change instructions of the form -Cfoo/baz and archive
     inclusions of the form @archive-file.  For example, the command line
           tar -c -f new.tar foo1 @old.tgz -C/tmp foo2
     will create a new archive new.tar.  tar will read the file foo1 from the
     current directory and add it to the output archive.  It will then read
     each entry from old.tgz and add those entries to the output archive.
     Finally, it will switch to the /tmp directory and add foo2 to the output
     archive.

     An input file in mtree(5) format can be used to create an output archive
     with arbitrary ownership, permissions, or names that differ from existing
     data on disk:

           $ cat input.mtree
           #mtree
           usr/bin uid=0 gid=0 mode=0755 type=dir
           usr/bin/ls uid=0 gid=0 mode=0755 type=file content=myls
           $ tar -cvf output.tar @input.mtree

     The --newer and --newer-mtime switches accept a variety of common date
     and time specifications, including “12 Mar 2005 7:14:29pm”, “2005-03-12
     19:14”, “5 minutes ago”, and “19:14 PST May 1”.

     The --options argument can be used to control various details of archive
     generation or reading.  For example, you can generate mtree output which
     only contains type, time, and uid keywords:
           tar -cf file.tar --format=mtree --options='!all,type,time,uid' dir
     or you can set the compression level used by gzip or xz compression:
           tar -czf file.tar --options='compression-level=9'.
     For more details, see the explanation of the archive_read_set_options()
     and archive_write_set_options() API calls that are described in
     archive_read(3) and archive_write(3).

COMPATIBILITY
     The bundled-arguments format is supported for compatibility with historic
     implementations.  It consists of an initial word (with no leading - char‐
     acter) in which each character indicates an option.  Arguments follow as
     separate words.  The order of the arguments must match the order of the
     corresponding characters in the bundled command word.  For example,
           tar tbf 32 file.tar
     specifies three flags t, b, and f.  The b and f flags both require argu‐
     ments, so there must be two additional items on the command line.  The 32
     is the argument to the b flag, and file.tar is the argument to the f
     flag.

     The mode options c, r, t, u, and x and the options b, f, l, m, o, v, and
     w comply with SUSv2.

     For maximum portability, scripts that invoke tar should use the bundled-
     argument format above, should limit themselves to the c, t, and x modes,
     and the b, f, m, v, and w options.

     Additional long options are provided to improve compatibility with other
     tar implementations.

SECURITY
     Certain security issues are common to many archiving programs, including
     tar.  In particular, carefully-crafted archives can request that tar
     extract files to locations outside of the target directory.  This can
     potentially be used to cause unwitting users to overwrite files they did
     not intend to overwrite.  If the archive is being extracted by the supe‐
     ruser, any file on the system can potentially be overwritten.  There are
     three ways this can happen.  Although tar has mechanisms to protect
     against each one, savvy users should be aware of the implications:

     ·      Archive entries can have absolute pathnames.  By default, tar
             removes the leading / character from filenames before restoring
             them to guard against this problem.

     ·      Archive entries can have pathnames that include .. components.
             By default, tar will not extract files containing .. components
             in their pathname.

     ·      Archive entries can exploit symbolic links to restore files to
             other directories.  An archive can restore a symbolic link to
             another directory, then use that link to restore a file into that
             directory.  To guard against this, tar checks each extracted path
             for symlinks.  If the final path element is a symlink, it will be
             removed and replaced with the archive entry.  If -U is specified,
             any intermediate symlink will also be unconditionally removed.
             If neither -U nor -P is specified, tar will refuse to extract the
             entry.
     To protect yourself, you should be wary of any archives that come from
     untrusted sources.  You should examine the contents of an archive with
           tar -tf filename
     before extraction.  You should use the -k option to ensure that tar will
     not overwrite any existing files or the -U option to remove any pre-
     existing files.  You should generally not extract archives while running
     with super-user privileges.  Note that the -P option to tar disables the
     security checks above and allows you to extract an archive while preserv‐
     ing any absolute pathnames, .. components, or symlinks to other directo‐
     ries.

SEE ALSO
     bzip2(1), compress(1), cpio(1), gzip(1), mt(1), pax(1), shar(1), xz(1),
     libarchive(3), libarchive-formats(5), tar(5)

STANDARDS
     There is no current POSIX standard for the tar command; it appeared in
     ISO/IEC 9945-1:1996 (“POSIX.1”) but was dropped from IEEE Std 1003.1-2001
     (“POSIX.1”).  The options supported by this implementation were developed
     by surveying a number of existing tar implementations as well as the old
     POSIX specification for tar and the current POSIX specification for pax.

     The ustar and pax interchange file formats are defined by IEEE Std
     1003.1-2001 (“POSIX.1”) for the pax command.

HISTORY
     A tar command appeared in Seventh Edition Unix, which was released in
     January, 1979.  There have been numerous other implementations, many of
     which extended the file format.  John Gilmore's pdtar public-domain
     implementation (circa November, 1987) was quite influential, and formed
     the basis of GNU tar.  GNU tar was included as the standard system tar in
     FreeBSD beginning with FreeBSD 1.0.

     This is a complete re-implementation based on the libarchive(3) library.
     It was first released with FreeBSD 5.4 in May, 2005.

BUGS
     This program follows ISO/IEC 9945-1:1996 (“POSIX.1”) for the definition
     of the -l option.  Note that GNU tar prior to version 1.15 treated -l as
     a synonym for the --one-file-system option.

     The -C dir option may differ from historic implementations.

     All archive output is written in correctly-sized blocks, even if the out‐
     put is being compressed.  Whether or not the last output block is padded
     to a full block size varies depending on the format and the output
     device.  For tar and cpio formats, the last block of output is padded to
     a full block size if the output is being written to standard output or to
     a character or block device such as a tape drive.  If the output is being
     written to a regular file, the last block will not be padded.  Many com‐
     pressors, including gzip(1) and bzip2(1), complain about the null padding
     when decompressing an archive created by tar, although they still extract
     it correctly.

     The compression and decompression is implemented internally, so there may
     be insignificant differences between the compressed output generated by
           tar -czf - file
     and that generated by
           tar -cf - file | gzip

     The default should be to read and write archives to the standard I/O
     paths, but tradition (and POSIX) dictates otherwise.

     The r and u modes require that the archive be uncompressed and located in
     a regular file on disk.  Other archives can be modified using c mode with
     the @archive-file extension.

     To archive a file called @foo or -foo you must specify it as ./@foo or
     ./-foo, respectively.

     In create mode, a leading ./ is always removed.  A leading / is stripped
     unless the -P option is specified.

     There needs to be better support for file selection on both create and
     extract.

     There is not yet any support for multi-volume archives.

     Converting between dissimilar archive formats (such as tar and cpio)
     using the @- convention can cause hard link information to be lost.
     (This is a consequence of the incompatible ways that different archive
     formats store hardlink information.)

BSD                           September 16, 2014                           BSD