File: tar.info, Node: tar invocation, Next: operations, Prev: Tutorial, Up: Top
3 Invoking GNU 'tar'
********************
This chapter is about how one invokes the GNU 'tar' command, from the
command synopsis (*note Synopsis::). There are numerous options, and
many styles for writing them. One mandatory option specifies the
operation 'tar' should perform (*note Operation Summary::), other
options are meant to detail how this operation should be performed
(*note Option Summary::). Non-option arguments are not always
interpreted the same way, depending on what the operation is.
You will find in this chapter everything about option styles and
rules for writing them (*note Styles::). On the other hand, operations
and options are fully described elsewhere, in other chapters. Here, you
will find only synthetic descriptions for operations and options,
together with pointers to other parts of the 'tar' manual.
Some options are so special they are fully described right in this
chapter. They have the effect of inhibiting the normal operation of
'tar' or else, they globally alter the amount of feedback the user
receives about what is going on. These are the '--help' and '--version'
(*note help::), '--verbose' (*note verbose::) and '--interactive'
options (*note interactive::).
* Menu:
* Synopsis::
* using tar options::
* Styles::
* All Options::
* help::
* defaults::
* verbose::
* checkpoints::
* warnings::
* interactive::
File: tar.info, Node: Synopsis, Next: using tar options, Up: tar invocation
3.1 General Synopsis of 'tar'
=============================
The GNU 'tar' program is invoked as either one of:
tar OPTION... [NAME]...
tar LETTER... [ARGUMENT]... [OPTION]... [NAME]...
The second form is for when old options are being used.
You can use 'tar' to store files in an archive, to extract them from
an archive, and to do other types of archive manipulation. The primary
argument to 'tar', which is called the "operation", specifies which
action to take. The other arguments to 'tar' are either "options",
which change the way 'tar' performs an operation, or file names or
archive members, which specify the files or members 'tar' is to act on.
You can actually type in arguments in any order, even if in this
manual the options always precede the other arguments, to make examples
easier to understand. Further, the option stating the main operation
mode (the 'tar' main command) is usually given first.
Each NAME in the synopsis above is interpreted as an archive member
name when the main command is one of '--compare' ('--diff', '-d'),
'--delete', '--extract' ('--get', '-x'), '--list' ('-t') or '--update'
('-u'). When naming archive members, you must give the exact name of
the member in the archive, as it is printed by '--list'. For '--append'
('-r') and '--create' ('-c'), these NAME arguments specify the names of
either files or directory hierarchies to place in the archive. These
files or hierarchies should already exist in the file system, prior to
the execution of the 'tar' command.
'tar' interprets relative file names as being relative to the working
directory. 'tar' will make all file names relative (by removing leading
slashes when archiving or restoring files), unless you specify otherwise
(using the '--absolute-names' option). *Note absolute::, for more
information about '--absolute-names'.
If you give the name of a directory as either a file name or a member
name, then 'tar' acts recursively on all the files and directories
beneath that directory. For example, the name '/' identifies all the
files in the file system to 'tar'.
The distinction between file names and archive member names is
especially important when shell globbing is used, and sometimes a source
of confusion for newcomers. *Note wildcards::, for more information
about globbing. The problem is that shells may only glob using existing
files in the file system. Only 'tar' itself may glob on archive
members, so when needed, you must ensure that wildcard characters reach
'tar' without being interpreted by the shell first. Using a backslash
before '*' or '?', or putting the whole argument between quotes, is
usually sufficient for this.
Even if NAMEs are often specified on the command line, they can also
be read from a text file in the file system, using the
'--files-from=FILE-OF-NAMES' ('-T FILE-OF-NAMES') option.
If you don't use any file name arguments, '--append' ('-r'),
'--delete' and '--concatenate' ('--catenate', '-A') will do nothing,
while '--create' ('-c') will usually yield a diagnostic and inhibit
'tar' execution. The other operations of 'tar' ('--list', '--extract',
'--compare', and '--update') will act on the entire contents of the
archive.
Besides successful exits, GNU 'tar' may fail for many reasons. Some
reasons correspond to bad usage, that is, when the 'tar' command line is
improperly written. Errors may be encountered later, while processing
the archive or the files. Some errors are recoverable, in which case
the failure is delayed until 'tar' has completed all its work. Some
errors are such that it would be not meaningful, or at least risky, to
continue processing: 'tar' then aborts processing immediately. All
abnormal exits, whether immediate or delayed, should always be clearly
diagnosed on 'stderr', after a line stating the nature of the error.
Possible exit codes of GNU 'tar' are summarized in the following
table:
0
'Successful termination'.
1
'Some files differ'. If tar was invoked with '--compare'
('--diff', '-d') command line option, this means that some files in
the archive differ from their disk counterparts (*note compare::).
If tar was given '--create', '--append' or '--update' option, this
exit code means that some files were changed while being archived
and so the resulting archive does not contain the exact copy of the
file set.
2
'Fatal error'. This means that some fatal, unrecoverable error
occurred.
If 'tar' has invoked a subprocess and that subprocess exited with a
nonzero exit code, 'tar' exits with that code as well. This can happen,
for example, if 'tar' was given some compression option (*note gzip::)
and the external compressor program failed. Another example is 'rmt'
failure during backup to the remote device (*note Remote Tape Server::).
File: tar.info, Node: using tar options, Next: Styles, Prev: Synopsis, Up: tar invocation
3.2 Using 'tar' Options
=======================
GNU 'tar' has a total of eight operating modes which allow you to
perform a variety of tasks. You are required to choose one operating
mode each time you employ the 'tar' program by specifying one, and only
one operation as an argument to the 'tar' command (the corresponding
options may be found at *note frequent operations:: and *note
Operations::). Depending on circumstances, you may also wish to
customize how the chosen operating mode behaves. For example, you may
wish to change the way the output looks, or the format of the files that
you wish to archive may require you to do something special in order to
make the archive look right.
You can customize and control 'tar''s performance by running 'tar'
with one or more options (such as '--verbose' ('-v'), which we used in
the tutorial). As we said in the tutorial, "options" are arguments to
'tar' which are (as their name suggests) optional. Depending on the
operating mode, you may specify one or more options. Different options
will have different effects, but in general they all change details of
the operation, such as archive format, archive name, or level of user
interaction. Some options make sense with all operating modes, while
others are meaningful only with particular modes. You will likely use
some options frequently, while you will only use others infrequently, or
not at all. (A full list of options is available in *note All
Options::.)
The 'TAR_OPTIONS' environment variable specifies default options to
be placed in front of any explicit options. For example, if
'TAR_OPTIONS' is '-v --unlink-first', 'tar' behaves as if the two
options '-v' and '--unlink-first' had been specified before any explicit
options. Option specifications are separated by whitespace. A
backslash escapes the next character, so it can be used to specify an
option containing whitespace or a backslash.
Note that 'tar' options are case sensitive. For example, the options
'-T' and '-t' are different; the first requires an argument for stating
the name of a file providing a list of NAMEs, while the second does not
require an argument and is another way to write '--list' ('-t').
In addition to the eight operations, there are many options to 'tar',
and three different styles for writing both: long (mnemonic) form, short
form, and old style. These styles are discussed below. Both the
options and the operations can be written in any of these three styles.
File: tar.info, Node: Styles, Next: All Options, Prev: using tar options, Up: tar invocation
3.3 The Three Option Styles
===========================
There are three styles for writing operations and options to the command
line invoking 'tar'. The different styles were developed at different
times during the history of 'tar'. These styles will be presented
below, from the most recent to the oldest.
Some options must take an argument(1). Where you _place_ the
arguments generally depends on which style of options you choose. We
will detail specific information relevant to each option style in the
sections on the different option styles, below. The differences are
subtle, yet can often be very important; incorrect option placement can
cause you to overwrite a number of important files. We urge you to note
these differences, and only use the option style(s) which makes the most
sense to you until you feel comfortable with the others.
Some options _may_ take an argument. Such options may have at most
long and short forms, they do not have old style equivalent. The rules
for specifying an argument for such options are stricter than those for
specifying mandatory arguments. Please, pay special attention to them.
* Menu:
* Long Options:: Long Option Style
* Short Options:: Short Option Style
* Old Options:: Old Option Style
* Mixing:: Mixing Option Styles
---------- Footnotes ----------
(1) For example, '--file' ('-f') takes the name of an archive file as
an argument. If you do not supply an archive file name, 'tar' will use
a default, but this can be confusing; thus, we recommend that you always
supply a specific archive file name.
File: tar.info, Node: Long Options, Next: Short Options, Up: Styles
3.3.1 Long Option Style
-----------------------
Each option has at least one "long" (or "mnemonic") name starting with
two dashes in a row, e.g., '--list'. The long names are more clear than
their corresponding short or old names. It sometimes happens that a
single long option has many different names which are synonymous, such
as '--compare' and '--diff'. In addition, long option names can be
given unique abbreviations. For example, '--cre' can be used in place
of '--create' because there is no other long option which begins with
'cre'. (One way to find this out is by trying it and seeing what
happens; if a particular abbreviation could represent more than one
option, 'tar' will tell you that that abbreviation is ambiguous and
you'll know that that abbreviation won't work. You may also choose to
run 'tar --help' to see a list of options. Be aware that if you run
'tar' with a unique abbreviation for the long name of an option you
didn't want to use, you are stuck; 'tar' will perform the command as
ordered.)
Long options are meant to be obvious and easy to remember, and their
meanings are generally easier to discern than those of their
corresponding short options (see below). For example:
$ tar --create --verbose --blocking-factor=20 --file=/dev/rmt0
gives a fairly good set of hints about what the command does, even for
those not fully acquainted with 'tar'.
Long options which require arguments take those arguments immediately
following the option name. There are two ways of specifying a mandatory
argument. It can be separated from the option name either by an equal
sign, or by any amount of white space characters. For example, the
'--file' option (which tells the name of the 'tar' archive) is given a
file such as 'archive.tar' as argument by using any of the following
notations: '--file=archive.tar' or '--file archive.tar'.
In contrast, optional arguments must always be introduced using an
equal sign. For example, the '--backup' option takes an optional
argument specifying backup type. It must be used as
'--backup=BACKUP-TYPE'.
File: tar.info, Node: Short Options, Next: Old Options, Prev: Long Options, Up: Styles
3.3.2 Short Option Style
------------------------
Most options also have a "short option" name. Short options start with
a single dash, and are followed by a single character, e.g., '-t' (which
is equivalent to '--list'). The forms are absolutely identical in
function; they are interchangeable.
The short option names are faster to type than long option names.
Short options which require arguments take their arguments
immediately following the option, usually separated by white space. It
is also possible to stick the argument right after the short option
name, using no intervening space. For example, you might write '-f archive.tar'
or '-farchive.tar' instead of using '--file=archive.tar'. Both
'--file=ARCHIVE-NAME' and '-f ARCHIVE-NAME' denote the option which
indicates a specific archive, here named 'archive.tar'.
Short options which take optional arguments take their arguments
immediately following the option letter, _without any intervening white
space characters_.
Short options' letters may be clumped together, but you are not
required to do this (as compared to old options; see below). When short
options are clumped as a set, use one (single) dash for them all, e.g.,
''tar' -cvf'. Only the last option in such a set is allowed to have an
argument(1).
When the options are separated, the argument for each option which
requires an argument directly follows that option, as is usual for Unix
programs. For example:
$ tar -c -v -b 20 -f /dev/rmt0
If you reorder short options' locations, be sure to move any
arguments that belong to them. If you do not move the arguments
properly, you may end up overwriting files.
---------- Footnotes ----------
(1) Clustering many options, the last of which has an argument, is a
rather opaque way to write options. Some wonder if GNU 'getopt' should
not even be made helpful enough for considering such usages as invalid.
File: tar.info, Node: Old Options, Next: Mixing, Prev: Short Options, Up: Styles
3.3.3 Old Option Style
----------------------
Like short options, "old options" are single letters. However, old
options must be written together as a single clumped set, without spaces
separating them or dashes preceding them(1). This set of letters must
be the first to appear on the command line, after the 'tar' program name
and some white space; old options cannot appear anywhere else. The
letter of an old option is exactly the same letter as the corresponding
short option. For example, the old option 't' is the same as the short
option '-t', and consequently, the same as the long option '--list'. So
for example, the command 'tar cv' specifies the option '-v' in addition
to the operation '-c'.
When options that need arguments are given together with the command,
all the associated arguments follow, in the same order as the options.
Thus, the example given previously could also be written in the old
style as follows:
$ tar cvbf 20 /dev/rmt0
Here, '20' is the argument of '-b' and '/dev/rmt0' is the argument of
'-f'.
On the other hand, this old style syntax makes it difficult to match
option letters with their corresponding arguments, and is often
confusing. In the command 'tar cvbf 20 /dev/rmt0', for example, '20' is
the argument for '-b', '/dev/rmt0' is the argument for '-f', and '-v'
does not have a corresponding argument. Even using short options like
in 'tar -c -v -b 20 -f /dev/rmt0' is clearer, putting all arguments next
to the option they pertain to.
If you want to reorder the letters in the old option argument, be
sure to reorder any corresponding argument appropriately.
This old way of writing 'tar' options can surprise even experienced
users. For example, the two commands:
tar cfz archive.tar.gz file
tar -cfz archive.tar.gz file
are quite different. The first example uses 'archive.tar.gz' as the
value for option 'f' and recognizes the option 'z'. The second example,
however, uses 'z' as the value for option 'f' -- probably not what was
intended.
Old options are kept for compatibility with old versions of 'tar'.
This second example could be corrected in many ways, among which the
following are equivalent:
tar -czf archive.tar.gz file
tar -cf archive.tar.gz -z file
tar cf archive.tar.gz -z file
As far as we know, all 'tar' programs, GNU and non-GNU, support old
options. GNU 'tar' supports them not only for historical reasons, but
also because many people are used to them. For compatibility with Unix
'tar', the first argument is always treated as containing command and
option letters even if it doesn't start with '-'. Thus, 'tar c' is
equivalent to 'tar -c': both of them specify the '--create' ('-c')
command to create an archive.
---------- Footnotes ----------
(1) Beware that if you precede options with a dash, you are
announcing the short option style instead of the old option style; short
options are decoded differently.
File: tar.info, Node: Mixing, Prev: Old Options, Up: Styles
3.3.4 Mixing Option Styles
--------------------------
All three styles may be intermixed in a single 'tar' command, so long as
the rules for each style are fully respected(1). Old style options and
either of the modern styles of options may be mixed within a single
'tar' command. However, old style options must be introduced as the
first arguments only, following the rule for old options (old options
must appear directly after the 'tar' command and some white space).
Modern options may be given only after all arguments to the old options
have been collected. If this rule is not respected, a modern option
might be falsely interpreted as the value of the argument to one of the
old style options.
For example, all the following commands are wholly equivalent, and
illustrate the many combinations and orderings of option styles.
tar --create --file=archive.tar
tar --create -f archive.tar
tar --create -farchive.tar
tar --file=archive.tar --create
tar --file=archive.tar -c
tar -c --file=archive.tar
tar -c -f archive.tar
tar -c -farchive.tar
tar -cf archive.tar
tar -cfarchive.tar
tar -f archive.tar --create
tar -f archive.tar -c
tar -farchive.tar --create
tar -farchive.tar -c
tar c --file=archive.tar
tar c -f archive.tar
tar c -farchive.tar
tar cf archive.tar
tar f archive.tar --create
tar f archive.tar -c
tar fc archive.tar
On the other hand, the following commands are _not_ equivalent to the
previous set:
tar -f -c archive.tar
tar -fc archive.tar
tar -fcarchive.tar
tar -farchive.tarc
tar cfarchive.tar
These last examples mean something completely different from what the
user intended (judging based on the example in the previous set which
uses long options, whose intent is therefore very clear). The first
four specify that the 'tar' archive would be a file named '-c', 'c',
'carchive.tar' or 'archive.tarc', respectively. The first two examples
also specify a single non-option, NAME argument having the value
'archive.tar'. The last example contains only old style option letters
(repeating option 'c' twice), not all of which are meaningful (eg., '.',
'h', or 'i'), with no argument value.
---------- Footnotes ----------
(1) Before GNU 'tar' version 1.11.6, a bug prevented intermixing old
style options with long options in some cases.
File: tar.info, Node: All Options, Next: help, Prev: Styles, Up: tar invocation
3.4 All 'tar' Options
=====================
The coming manual sections contain an alphabetical listing of all 'tar'
operations and options, with brief descriptions and cross-references to
more in-depth explanations in the body of the manual. They also contain
an alphabetically arranged table of the short option forms with their
corresponding long option. You can use this table as a reference for
deciphering 'tar' commands in scripts.
* Menu:
* Operation Summary::
* Option Summary::
* Short Option Summary::
File: tar.info, Node: Operation Summary, Next: Option Summary, Up: All Options
3.4.1 Operations
----------------
'--append'
'-r'
Appends files to the end of the archive. *Note append::.
'--catenate'
'-A'
Same as '--concatenate'. *Note concatenate::.
'--compare'
'-d'
Compares archive members with their counterparts in the file
system, and reports differences in file size, mode, owner,
modification date and contents. *Note compare::.
'--concatenate'
'-A'
Appends other 'tar' archives to the end of the archive. *Note
concatenate::.
'--create'
'-c'
Creates a new 'tar' archive. *Note create::.
'--delete'
Deletes members from the archive. Don't try this on an archive on
a tape! *Note delete::.
'--diff'
'-d'
Same '--compare'. *Note compare::.
'--extract'
'-x'
Extracts members from the archive into the file system. *Note
extract::.
'--get'
'-x'
Same as '--extract'. *Note extract::.
'--list'
'-t'
Lists the members in an archive. *Note list::.
'--update'
'-u'
Adds files to the end of the archive, but only if they are newer
than their counterparts already in the archive, or if they do not
already exist in the archive. *Note update::.
File: tar.info, Node: Option Summary, Next: Short Option Summary, Prev: Operation Summary, Up: All Options
3.4.2 'tar' Options
-------------------
'--absolute-names'
'-P'
Normally when creating an archive, 'tar' strips an initial '/' from
member names. This option disables that behavior. *Note
absolute::.
'--acls'
Causes 'tar' to store/restore/list POSIX ACL's. *Note
Attributes::.
'--after-date'
(See '--newer', *note after::)
'--anchored'
A pattern must match an initial subsequence of the name's
components. *Note controlling pattern-matching::.
'--atime-preserve'
'--atime-preserve=replace'
'--atime-preserve=system'
Attempt to preserve the access time of files when reading them.
This option currently is effective only on files that you own,
unless you have superuser privileges.
'--atime-preserve=replace' remembers the access time of a file
before reading it, and then restores the access time afterwards.
This may cause problems if other programs are reading the file at
the same time, as the times of their accesses will be lost. On
most platforms restoring the access time also requires 'tar' to
restore the data modification time too, so this option may also
cause problems if other programs are writing the file at the same
time ('tar' attempts to detect this situation, but cannot do so
reliably due to race conditions). Worse, on most platforms
restoring the access time also updates the status change time,
which means that this option is incompatible with incremental
backups.
'--atime-preserve=system' avoids changing time stamps on files,
without interfering with time stamp updates caused by other
programs, so it works better with incremental backups. However, it
requires a special 'O_NOATIME' option from the underlying operating
and file system implementation, and it also requires that searching
directories does not update their access times. As of this writing
(November 2005) this works only with Linux, and only with Linux
kernels 2.6.8 and later. Worse, there is currently no reliable way
to know whether this feature actually works. Sometimes 'tar' knows
that it does not work, and if you use '--atime-preserve=system'
then 'tar' complains and exits right away. But other times 'tar'
might think that the option works when it actually does not.
Currently '--atime-preserve' with no operand defaults to
'--atime-preserve=replace', but this may change in the future as
support for '--atime-preserve=system' improves.
If your operating or file system does not support
'--atime-preserve=system', you might be able to preserve access
times reliably by using the 'mount' command. For example, you can
mount the file system read-only, or access the file system via a
read-only loopback mount, or use the 'noatime' mount option
available on some systems. However, mounting typically requires
superuser privileges and can be a pain to manage.
'--auto-compress'
'-a'
During a '--create' operation, enables automatic compressed format
recognition based on the archive suffix. The effect of this option
is cancelled by '--no-auto-compress'. *Note gzip::.
'--backup=BACKUP-TYPE'
Rather than deleting files from the file system, 'tar' will back
them up using simple or numbered backups, depending upon
BACKUP-TYPE. *Note backup::.
'--block-number'
'-R'
With this option present, 'tar' prints error messages for read
errors with the block number in the archive file. *Note
block-number::.
'--blocking-factor=BLOCKING'
'-b BLOCKING'
Sets the blocking factor 'tar' uses to BLOCKING x 512 bytes per
record. *Note Blocking Factor::.
'--bzip2'
'-j'
This option tells 'tar' to read or write archives through 'bzip2'.
*Note gzip::.
'--check-device'
Check device numbers when creating a list of modified files for
incremental archiving. This is the default. *Note device
numbers::, for a detailed description.
'--checkpoint[=NUMBER]'
This option directs 'tar' to print periodic checkpoint messages as
it reads through the archive. It is intended for when you want a
visual indication that 'tar' is still running, but don't want to
see '--verbose' output. You can also instruct 'tar' to execute a
list of actions on each checkpoint, see '--checkpoint-action'
below. For a detailed description, see *note checkpoints::.
'--checkpoint-action=ACTION'
Instruct 'tar' to execute an action upon hitting a breakpoint.
Here we give only a brief outline. *Note checkpoints::, for a
complete description.
The ACTION argument can be one of the following:
bell
Produce an audible bell on the console.
dot
.
Print a single dot on the standard listing stream.
echo
Display a textual message on the standard error, with the
status and number of the checkpoint. This is the default.
echo=STRING
Display STRING on the standard error. Before output, the
string is subject to meta-character expansion.
exec=COMMAND
Execute the given COMMAND.
sleep=TIME
Wait for TIME seconds.
ttyout=STRING
Output STRING on the current console ('/dev/tty').
Several '--checkpoint-action' options can be specified. The
supplied actions will be executed in order of their appearance in
the command line.
Using '--checkpoint-action' without '--checkpoint' assumes default
checkpoint frequency of one checkpoint per 10 records.
'--check-links'
'-l'
If this option was given, 'tar' will check the number of links
dumped for each processed file. If this number does not match the
total number of hard links for the file, a warning message will be
output (1).
*Note hard links::.
'--compress'
'--uncompress'
'-Z'
'tar' will use the 'compress' program when reading or writing the
archive. This allows you to directly act on archives while saving
space. *Note gzip::.
'--confirmation'
(See '--interactive'.) *Note interactive::.
'--delay-directory-restore'
Delay setting modification times and permissions of extracted
directories until the end of extraction. *Note Directory
Modification Times and Permissions::.
'--dereference'
'-h'
When reading or writing a file to be archived, 'tar' accesses the
file that a symbolic link points to, rather than the symlink
itself. *Note dereference::.
'--directory=DIR'
'-C DIR'
When this option is specified, 'tar' will change its current
directory to DIR before performing any operations. When this
option is used during archive creation, it is order sensitive.
*Note directory::.
'--exclude=PATTERN'
When performing operations, 'tar' will skip files that match
PATTERN. *Note exclude::.
'--exclude-backups'
Exclude backup and lock files. *Note exclude-backups: exclude.
'--exclude-from=FILE'
'-X FILE'
Similar to '--exclude', except 'tar' will use the list of patterns
in the file FILE. *Note exclude::.
'--exclude-caches'
Exclude from dump any directory containing a valid cache directory
tag file, but still dump the directory node and the tag file
itself.
*Note exclude-caches: exclude.
'--exclude-caches-under'
Exclude from dump any directory containing a valid cache directory
tag file, but still dump the directory node itself.
*Note exclude::.
'--exclude-caches-all'
Exclude from dump any directory containing a valid cache directory
tag file. *Note exclude::.
'--exclude-tag=FILE'
Exclude from dump any directory containing file named FILE, but
dump the directory node and FILE itself. *Note exclude-tag:
exclude.
'--exclude-tag-under=FILE'
Exclude from dump the contents of any directory containing file
named FILE, but dump the directory node itself. *Note
exclude-tag-under: exclude.
'--exclude-tag-all=FILE'
Exclude from dump any directory containing file named FILE. *Note
exclude-tag-all: exclude.
'--exclude-vcs'
Exclude from dump directories and files, that are internal for some
widely used version control systems.
*Note exclude-vcs: exclude.
'--file=ARCHIVE'
'-f ARCHIVE'
'tar' will use the file ARCHIVE as the 'tar' archive it performs
operations on, rather than 'tar''s compilation dependent default.
*Note file tutorial::.
'--files-from=FILE'
'-T FILE'
'tar' will use the contents of FILE as a list of archive members or
files to operate on, in addition to those specified on the
command-line. *Note files::.
'--force-local'
Forces 'tar' to interpret the file name given to '--file' as a
local file, even if it looks like a remote tape drive name. *Note
local and remote archives::.
'--format=FORMAT'
'-H FORMAT'
Selects output archive format. FORMAT may be one of the following:
'v7'
Creates an archive that is compatible with Unix V7 'tar'.
'oldgnu'
Creates an archive that is compatible with GNU 'tar' version
1.12 or earlier.
'gnu'
Creates archive in GNU tar 1.13 format. Basically it is the
same as 'oldgnu' with the only difference in the way it
handles long numeric fields.
'ustar'
Creates a POSIX.1-1988 compatible archive.
'posix'
Creates a POSIX.1-2001 archive.
*Note Formats::, for a detailed discussion of these formats.
'--full-time'
This option instructs 'tar' to print file times to their full
resolution. Usually this means 1-second resolution, but that
depends on the underlying file system. The '--full-time' option
takes effect only when detailed output (verbosity level 2 or
higher) has been requested using the '--verbose' option, e.g., when
listing or extracting archives:
$ tar -t -v --full-time -f archive.tar
or, when creating an archive:
$ tar -c -vv --full-time -f archive.tar .
Notice, thar when creating the archive you need to specify
'--verbose' twice to get a detailed output (*note verbose
tutorial::).
'--group=GROUP'
Files added to the 'tar' archive will have a group ID of GROUP,
rather than the group from the source file. GROUP is first decoded
as a group symbolic name, but if this interpretation fails, it has
to be a decimal numeric group ID. *Note override::.
Also see the comments for the '--owner=USER' option.
'--gzip'
'--gunzip'
'--ungzip'
'-z'
This option tells 'tar' to read or write archives through 'gzip',
allowing 'tar' to directly operate on several kinds of compressed
archives transparently. *Note gzip::.
'--hard-dereference'
When creating an archive, dereference hard links and store the
files they refer to, instead of creating usual hard link members.
*Note hard links::.
'--help'
'-?'
'tar' will print out a short message summarizing the operations and
options to 'tar' and exit. *Note help::.
'--ignore-case'
Ignore case when matching member or file names with patterns.
*Note controlling pattern-matching::.
'--ignore-command-error'
Ignore exit codes of subprocesses. *Note Writing to an External
Program::.
'--ignore-failed-read'
Do not exit unsuccessfully merely because an unreadable file was
encountered. *Note Reading::.
'--ignore-zeros'
'-i'
With this option, 'tar' will ignore zeroed blocks in the archive,
which normally signals EOF. *Note Reading::.
'--incremental'
'-G'
Informs 'tar' that it is working with an old GNU-format incremental
backup archive. It is intended primarily for backwards
compatibility only. *Note Incremental Dumps::, for a detailed
discussion of incremental archives.
'--index-file=FILE'
Send verbose output to FILE instead of to standard output.
'--info-script=SCRIPT-FILE'
'--new-volume-script=SCRIPT-FILE'
'-F SCRIPT-FILE'
When 'tar' is performing multi-tape backups, SCRIPT-FILE is run at
the end of each tape. If SCRIPT-FILE exits with nonzero status,
'tar' fails immediately. *Note info-script::, for a detailed
discussion of SCRIPT-FILE.
'--interactive'
'--confirmation'
'-w'
Specifies that 'tar' should ask the user for confirmation before
performing potentially destructive options, such as overwriting
files. *Note interactive::.
'--keep-directory-symlink'
This option changes the behavior of tar when it encounters a
symlink with the same name as the directory that it is about to
extract. By default, in this case tar would first remove the
symlink and then proceed extracting the directory.
The '--keep-directory-symlink' option disables this behavior and
instructs tar to follow symlinks to directories when extracting
from the archive.
It is mainly intended to provide compatibility with the Slackware
installation scripts.
'--keep-newer-files'
Do not replace existing files that are newer than their archive
copies when extracting files from an archive.
'--keep-old-files'
'-k'
Do not overwrite existing files when extracting files from an
archive. Return error if such files exist. See also *note
--skip-old-files::.
*Note Keep Old Files::.
'--label=NAME'
'-V NAME'
When creating an archive, instructs 'tar' to write NAME as a name
record in the archive. When extracting or listing archives, 'tar'
will only operate on archives that have a label matching the
pattern specified in NAME. *Note Tape Files::.
'--level=N'
Force incremental backup of level N. As of GNU 'tar' version 1.26,
the option '--level=0' truncates the snapshot file, thereby forcing
the level 0 dump. Other values of N are effectively ignored.
*Note --level=0::, for details and examples.
The use of this option is valid only in conjunction with the
'--listed-incremental' option. *Note Incremental Dumps::, for a
detailed description.
'--listed-incremental=SNAPSHOT-FILE'
'-g SNAPSHOT-FILE'
During a '--create' operation, specifies that the archive that
'tar' creates is a new GNU-format incremental backup, using
SNAPSHOT-FILE to determine which files to backup. With other
operations, informs 'tar' that the archive is in incremental
format. *Note Incremental Dumps::.
'--lzip'
This option tells 'tar' to read or write archives through 'lzip'.
*Note gzip::.
'--lzma'
This option tells 'tar' to read or write archives through 'lzma'.
*Note gzip::.
'--lzop'
This option tells 'tar' to read or write archives through 'lzop'.
*Note gzip::.
'--mode=PERMISSIONS'
When adding files to an archive, 'tar' will use PERMISSIONS for the
archive members, rather than the permissions from the files.
PERMISSIONS can be specified either as an octal number or as
symbolic permissions, like with 'chmod'. *Note override::.
'--mtime=DATE'
When adding files to an archive, 'tar' will use DATE as the
modification time of members when creating archives, instead of
their actual modification times. The value of DATE can be either a
textual date representation (*note Date input formats::) or a name
of the existing file, starting with '/' or '.'. In the latter
case, the modification time of that file is used. *Note
override::.
'--multi-volume'
'-M'
Informs 'tar' that it should create or otherwise operate on a
multi-volume 'tar' archive. *Note Using Multiple Tapes::.
'--new-volume-script'
(see '--info-script')
'--newer=DATE'
'--after-date=DATE'
'-N'
When creating an archive, 'tar' will only add files that have
changed since DATE. If DATE begins with '/' or '.', it is taken to
be the name of a file whose data modification time specifies the
date. *Note after::.
'--newer-mtime=DATE'
Like '--newer', but add only files whose contents have changed (as
opposed to just '--newer', which will also back up files for which
any status information has changed). *Note after::.
'--no-acls'
Causes 'tar' not to store, extract or list POSIX ACL's. *Note
Attributes::.
'--no-anchored'
An exclude pattern can match any subsequence of the name's
components. *Note controlling pattern-matching::.
'--no-auto-compress'
Disables automatic compressed format recognition based on the
archive suffix. *Note --auto-compress::. *Note gzip::.
'--no-check-device'
Do not check device numbers when creating a list of modified files
for incremental archiving. *Note device numbers::, for a detailed
description.
'--no-delay-directory-restore'
Modification times and permissions of extracted directories are set
when all files from this directory have been extracted. This is
the default. *Note Directory Modification Times and Permissions::.
'--no-ignore-case'
Use case-sensitive matching. *Note controlling pattern-matching::.
'--no-ignore-command-error'
Print warnings about subprocesses that terminated with a nonzero
exit code. *Note Writing to an External Program::.
'--no-null'
If the '--null' option was given previously, this option cancels
its effect, so that any following '--files-from' options will
expect their file lists to be newline-terminated.
'--no-overwrite-dir'
Preserve metadata of existing directories when extracting files
from an archive. *Note Overwrite Old Files::.
'--no-quote-chars=STRING'
Remove characters listed in STRING from the list of quoted
characters set by the previous '--quote-chars' option (*note
quoting styles::).
'--no-recursion'
With this option, 'tar' will not recurse into directories. *Note
recurse::.
'--no-same-owner'
'-o'
When extracting an archive, do not attempt to preserve the owner
specified in the 'tar' archive. This the default behavior for
ordinary users.
'--no-same-permissions'
When extracting an archive, subtract the user's umask from files
from the permissions specified in the archive. This is the default
behavior for ordinary users.
'--no-seek'
The archive media does not support seeks to arbitrary locations.
Usually 'tar' determines automatically whether the archive can be
seeked or not. Use this option to disable this mechanism.
'--no-selinux'
Causes 'tar' not to store, extract or list SELinux security
context. *Note Attributes::.
'--no-unquote'
Treat all input file or member names literally, do not interpret
escape sequences. *Note input name quoting::.
'--no-xattrs'
Causes 'tar' not to store, extract or list xattrs. *Note
Attributes::.
'--no-wildcards'
Do not use wildcards. *Note controlling pattern-matching::.
'--no-wildcards-match-slash'
Wildcards do not match '/'. *Note controlling pattern-matching::.
'--null'
When 'tar' is using the '--files-from' option, this option
instructs 'tar' to expect file names terminated with NUL, so 'tar'
can correctly work with file names that contain newlines. *Note
nul::.
'--numeric-owner'
This option will notify 'tar' that it should use numeric user and
group IDs when creating a 'tar' file, rather than names. *Note
Attributes::.
'-o'
The function of this option depends on the action 'tar' is
performing. When extracting files, '-o' is a synonym for
'--no-same-owner', i.e., it prevents 'tar' from restoring ownership
of files being extracted.
When creating an archive, it is a synonym for '--old-archive'.
This behavior is for compatibility with previous versions of GNU
'tar', and will be removed in future releases.
*Note Changes::, for more information.
'--occurrence[=NUMBER]'
This option can be used in conjunction with one of the subcommands
'--delete', '--diff', '--extract' or '--list' when a list of files
is given either on the command line or via '-T' option.
This option instructs 'tar' to process only the NUMBERth occurrence
of each named file. NUMBER defaults to 1, so
tar -x -f archive.tar --occurrence filename
will extract the first occurrence of the member 'filename' from
'archive.tar' and will terminate without scanning to the end of the
archive.
'--old-archive'
Synonym for '--format=v7'.
'--one-file-system'
Used when creating an archive. Prevents 'tar' from recursing into
directories that are on different file systems from the current
directory.
'--overwrite'
Overwrite existing files and directory metadata when extracting
files from an archive. *Note Overwrite Old Files::.
'--overwrite-dir'
Overwrite the metadata of existing directories when extracting
files from an archive. *Note Overwrite Old Files::.
'--owner=USER'
Specifies that 'tar' should use USER as the owner of members when
creating archives, instead of the user associated with the source
file. USER is first decoded as a user symbolic name, but if this
interpretation fails, it has to be a decimal numeric user ID.
*Note override::.
This option does not affect extraction from archives.
'--pax-option=KEYWORD-LIST'
This option enables creation of the archive in POSIX.1-2001 format
(*note posix::) and modifies the way 'tar' handles the extended
header keywords. KEYWORD-LIST is a comma-separated list of keyword
options. *Note PAX keywords::, for a detailed discussion.
'--portability'
'--old-archive'
Synonym for '--format=v7'.
'--posix'
Same as '--format=posix'.
'--preserve'
Synonymous with specifying both '--preserve-permissions' and
'--same-order'. *Note Setting Access Permissions::.
'--preserve-order'
(See '--same-order'; *note Reading::.)
'--preserve-permissions'
'--same-permissions'
'-p'
When 'tar' is extracting an archive, it normally subtracts the
users' umask from the permissions specified in the archive and uses
that number as the permissions to create the destination file.
Specifying this option instructs 'tar' that it should use the
permissions directly from the archive. *Note Setting Access
Permissions::.
'--quote-chars=STRING'
Always quote characters from STRING, even if the selected quoting
style would not quote them (*note quoting styles::).
'--quoting-style=STYLE'
Set quoting style to use when printing member and file names (*note
quoting styles::). Valid STYLE values are: 'literal', 'shell',
'shell-always', 'c', 'escape', 'locale', and 'clocale'. Default
quoting style is 'escape', unless overridden while configuring the
package.
'--read-full-records'
'-B'
Specifies that 'tar' should reblock its input, for reading from
pipes on systems with buggy implementations. *Note Reading::.
'--record-size=SIZE[SUF]'
Instructs 'tar' to use SIZE bytes per record when accessing the
archive. The argument can be suffixed with a "size suffix", e.g.
'--record-size=10K' for 10 Kilobytes. *Note Table 9.1:
size-suffixes, for a list of valid suffixes. *Note Blocking
Factor::, for a detailed description of this option.
'--recursion'
With this option, 'tar' recurses into directories (default). *Note
recurse::.
'--recursive-unlink'
Remove existing directory hierarchies before extracting directories
of the same name from the archive. *Note Recursive Unlink::.
'--remove-files'
Directs 'tar' to remove the source file from the file system after
appending it to an archive. *Note remove files::.
'--restrict'
Disable use of some potentially harmful 'tar' options. Currently
this option disables shell invocation from multi-volume menu (*note
Using Multiple Tapes::).
'--rmt-command=CMD'
Notifies 'tar' that it should use CMD instead of the default
'/usr/libexec/rmt' (*note Remote Tape Server::).
'--rsh-command=CMD'
Notifies 'tar' that is should use CMD to communicate with remote
devices. *Note Device::.
'--same-order'
'--preserve-order'
'-s'
This option is an optimization for 'tar' when running on machines
with small amounts of memory. It informs 'tar' that the list of
file arguments has already been sorted to match the order of files
in the archive. *Note Reading::.
'--same-owner'
When extracting an archive, 'tar' will attempt to preserve the
owner specified in the 'tar' archive with this option present.
This is the default behavior for the superuser; this option has an
effect only for ordinary users. *Note Attributes::.
'--same-permissions'
(See '--preserve-permissions'; *note Setting Access Permissions::.)
'--seek'
'-n'
Assume that the archive media supports seeks to arbitrary
locations. Usually 'tar' determines automatically whether the
archive can be seeked or not. This option is intended for use in
cases when such recognition fails. It takes effect only if the
archive is open for reading (e.g. with '--list' or '--extract'
options).
'--selinux'
Causes 'tar' to store, extract or list SELinux security context.
*Note Attributes::.
'--show-defaults'
Displays the default options used by 'tar' and exits successfully.
This option is intended for use in shell scripts. Here is an
example of what you can see using this option:
$ tar --show-defaults
--format=gnu -f- -b20 --quoting-style=escape
--rmt-command=/usr/libexec/rmt --rsh-command=/usr/bin/rsh
Notice, that this option outputs only one line. The example output
above has been split to fit page boundaries.
'--show-omitted-dirs'
Instructs 'tar' to mention the directories it is skipping when
operating on a 'tar' archive. *Note show-omitted-dirs::.
'--show-transformed-names'
'--show-stored-names'
Display file or member names after applying any transformations
(*note transform::). In particular, when used in conjunction with
one of the archive creation operations it instructs 'tar' to list
the member names stored in the archive, as opposed to the actual
file names. *Note listing member and file names::.
'--skip-old-files'
Do not overwrite existing files when extracting files from an
archive. *Note Keep Old Files::.
This option differs from '--keep-old-files' in that it does not
treat such files as an error, instead it just silently avoids
overwriting them.
The '--warning=existing-file' option can be used together with this
option to produce warning messages about existing old files (*note
warnings::).
'--sparse'
'-S'
Invokes a GNU extension when adding files to an archive that
handles sparse files efficiently. *Note sparse::.
'--sparse-version=VERSION'
Specifies the "format version" to use when archiving sparse files.
Implies '--sparse'. *Note sparse::. For the description of the
supported sparse formats, *Note Sparse Formats::.
'--starting-file=NAME'
'-K NAME'
This option affects extraction only; 'tar' will skip extracting
files in the archive until it finds one that matches NAME. *Note
Scarce::.
'--strip-components=NUMBER'
Strip given NUMBER of leading components from file names before
extraction. For example, if archive 'archive.tar' contained
'/some/file/name', then running
tar --extract --file archive.tar --strip-components=2
would extract this file to file 'name'.
'--suffix=SUFFIX'
Alters the suffix 'tar' uses when backing up files from the default
'~'. *Note backup::.
'--tape-length=NUM[SUF]'
'-L NUM[SUF]'
Specifies the length of tapes that 'tar' is writing as being NUM x 1024
bytes long. If optional SUF is given, it specifies a
multiplicative factor to be used instead of 1024. For example,
'-L2M' means 2 megabytes. *Note Table 9.1: size-suffixes, for a
list of allowed suffixes. *Note Using Multiple Tapes::, for a
detailed discussion of this option.
'--test-label'
Reads the volume label. If an argument is specified, test whether
it matches the volume label. *Note --test-label option::.
'--to-command=COMMAND'
During extraction 'tar' will pipe extracted files to the standard
input of COMMAND. *Note Writing to an External Program::.
'--to-stdout'
'-O'
During extraction, 'tar' will extract files to stdout rather than
to the file system. *Note Writing to Standard Output::.
'--totals[=SIGNO]'
Displays the total number of bytes transferred when processing an
archive. If an argument is given, these data are displayed on
request, when signal SIGNO is delivered to 'tar'. *Note totals::.
'--touch'
'-m'
Sets the data modification time of extracted files to the
extraction time, rather than the data modification time stored in
the archive. *Note Data Modification Times::.
'--transform=SED-EXPR'
'--xform=SED-EXPR'
Transform file or member names using 'sed' replacement expression
SED-EXPR. For example,
$ tar cf archive.tar --transform 's,^\./,usr/,' .
will add to 'archive' files from the current working directory,
replacing initial './' prefix with 'usr/'. For the detailed
discussion, *Note transform::.
To see transformed member names in verbose listings, use
'--show-transformed-names' option (*note show-transformed-names::).
'--uncompress'
(See '--compress', *note gzip::)
'--ungzip'
(See '--gzip', *note gzip::)
'--unlink-first'
'-U'
Directs 'tar' to remove the corresponding file from the file system
before extracting it from the archive. *Note Unlink First::.
'--unquote'
Enable unquoting input file or member names (default). *Note input
name quoting::.
'--use-compress-program=PROG'
'-I=PROG'
Instructs 'tar' to access the archive through PROG, which is
presumed to be a compression program of some sort. *Note gzip::.
'--utc'
Display file modification dates in UTC. This option implies
'--verbose'.
'--verbose'
'-v'
Specifies that 'tar' should be more verbose about the operations it
is performing. This option can be specified multiple times for
some operations to increase the amount of information displayed.
*Note verbose::.
'--verify'
'-W'
Verifies that the archive was correctly written when creating an
archive. *Note verify::.
'--version'
Print information about the program's name, version, origin and
legal status, all on standard output, and then exit successfully.
*Note help::.
'--volno-file=FILE'
Used in conjunction with '--multi-volume'. 'tar' will keep track
of which volume of a multi-volume archive it is working in FILE.
*Note volno-file::.
'--warning=KEYWORD'
Enable or disable warning messages identified by KEYWORD. The
messages are suppressed if KEYWORD is prefixed with 'no-'. *Note
warnings::.
'--xattrs'
Causes 'tar' to store, restore or list extended file attributes.
For more info see *Note Attributes::.
'--wildcards'
Use wildcards when matching member names with patterns. *Note
controlling pattern-matching::.
'--wildcards-match-slash'
Wildcards match '/'. *Note controlling pattern-matching::.
'--xz'
'-J'
Use 'xz' for compressing or decompressing the archives. *Note
gzip::.
---------- Footnotes ----------
(1) Earlier versions of GNU 'tar' understood '-l' as a synonym for
'--one-file-system'. The current semantics, which complies to UNIX98,
was introduced with version 1.15.91. *Note Changes::, for more
information.
File: tar.info, Node: Short Option Summary, Prev: Option Summary, Up: All Options
3.4.3 Short Options Cross Reference
-----------------------------------
Here is an alphabetized list of all of the short option forms, matching
them with the equivalent long option.
Short Option Reference
--------------------------------------------------------------------------
-A *note --concatenate::.
-B *note --read-full-records::.
-C *note --directory::.
-F *note --info-script::.
-G *note --incremental::.
-J *note --xz::.
-K *note --starting-file::.
-L *note --tape-length::.
-M *note --multi-volume::.
-N *note --newer::.
-O *note --to-stdout::.
-P *note --absolute-names::.
-R *note --block-number::.
-S *note --sparse::.
-T *note --files-from::.
-U *note --unlink-first::.
-V *note --label::.
-W *note --verify::.
-X *note --exclude-from::.
-Z *note --compress::.
-b *note --blocking-factor::.
-c *note --create::.
-d *note --compare::.
-f *note --file::.
-g *note --listed-incremental::.
-h *note --dereference::.
-i *note --ignore-zeros::.
-j *note --bzip2::.
-k *note --keep-old-files::.
-l *note --check-links::.
-m *note --touch::.
-o When creating, *note --no-same-owner::, when extracting
-- *note --portability::.
The latter usage is deprecated. It is retained for
compatibility with the earlier versions of GNU 'tar'.
In future releases '-o' will be equivalent to
'--no-same-owner' only.
-p *note --preserve-permissions::.
-r *note --append::.
-s *note --same-order::.
-t *note --list::.
-u *note --update::.
-v *note --verbose::.
-w *note --interactive::.
-x *note --extract::.
-z *note --gzip::.
File: tar.info, Node: help, Next: defaults, Prev: All Options, Up: tar invocation
3.5 GNU 'tar' documentation
===========================
Being careful, the first thing is really checking that you are using GNU
'tar', indeed. The '--version' option causes 'tar' to print information
about its name, version, origin and legal status, all on standard
output, and then exit successfully. For example, 'tar --version' might
print:
tar (GNU tar) 1.26
Copyright (C) 2010 Free Software Foundation, Inc.
Copyright (C) 2010 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>;.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Written by John Gilmore and Jay Fenlason.
The first occurrence of 'tar' in the result above is the program name in
the package (for example, 'rmt' is another program), while the second
occurrence of 'tar' is the name of the package itself, containing
possibly many programs. The package is currently named 'tar', after the
name of the main program it contains(1).
Another thing you might want to do is checking the spelling or
meaning of some particular 'tar' option, without resorting to this
manual, for once you have carefully read it. GNU 'tar' has a short help
feature, triggerable through the '--help' option. By using this option,
'tar' will print a usage message listing all available options on
standard output, then exit successfully, without doing anything else and
ignoring all other options. Even if this is only a brief summary, it
may be several screens long. So, if you are not using some kind of
scrollable window, you might prefer to use something like:
$ tar --help | less
presuming, here, that you like using 'less' for a pager. Other popular
pagers are 'more' and 'pg'. If you know about some KEYWORD which
interests you and do not want to read all the '--help' output, another
common idiom is doing:
tar --help | grep KEYWORD
for getting only the pertinent lines. Notice, however, that some 'tar'
options have long description lines and the above command will list only
the first of them.
The exact look of the option summary displayed by 'tar --help' is
configurable. *Note Configuring Help Summary::, for a detailed
description.
If you only wish to check the spelling of an option, running 'tar
--usage' may be a better choice. This will display a terse list of
'tar' options without accompanying explanations.
The short help output is quite succinct, and you might have to get
back to the full documentation for precise points. If you are reading
this paragraph, you already have the 'tar' manual in some form. This
manual is available in a variety of forms from
<http://www.gnu.org/software/tar/manual>;. It may be printed out of the
GNU 'tar' distribution, provided you have TeX already installed
somewhere, and a laser printer around. Just configure the distribution,
execute the command 'make dvi', then print 'doc/tar.dvi' the usual way
(contact your local guru to know how). If GNU 'tar' has been
conveniently installed at your place, this manual is also available in
interactive, hypertextual form as an Info file. Just call 'info tar'
or, if you do not have the 'info' program handy, use the Info reader
provided within GNU Emacs, calling 'tar' from the main Info menu.
There is currently no 'man' page for GNU 'tar'. If you observe such
a 'man' page on the system you are running, either it does not belong to
GNU 'tar', or it has not been produced by GNU. Some package maintainers
convert 'tar --help' output to a man page, using 'help2man'. In any
case, please bear in mind that the authoritative source of information
about GNU 'tar' is this Texinfo documentation.
---------- Footnotes ----------
(1) There are plans to merge the 'cpio' and 'tar' packages into a
single one which would be called 'paxutils'. So, who knows if, one of
this days, the '--version' would not output 'tar (GNU paxutils) 3.2'.
File: tar.info, Node: defaults, Next: verbose, Prev: help, Up: tar invocation
3.6 Obtaining GNU 'tar' default values
======================================
GNU 'tar' has some predefined defaults that are used when you do not
explicitly specify another values. To obtain a list of such defaults,
use '--show-defaults' option. This will output the values in the form
of 'tar' command line options:
$ tar --show-defaults
--format=gnu -f- -b20 --quoting-style=escape
--rmt-command=/etc/rmt --rsh-command=/usr/bin/rsh
Notice, that this option outputs only one line. The example output
above has been split to fit page boundaries.
The above output shows that this version of GNU 'tar' defaults to using
'gnu' archive format (*note Formats::), it uses standard output as the
archive, if no '--file' option has been given (*note file tutorial::),
the default blocking factor is 20 (*note Blocking Factor::). It also
shows the default locations where 'tar' will look for 'rmt' and 'rsh'
binaries.
File: tar.info, Node: verbose, Next: checkpoints, Prev: defaults, Up: tar invocation
3.7 Checking 'tar' progress
===========================
Typically, 'tar' performs most operations without reporting any
information to the user except error messages. When using 'tar' with
many options, particularly ones with complicated or difficult-to-predict
behavior, it is possible to make serious mistakes. 'tar' provides
several options that make observing 'tar' easier. These options cause
'tar' to print information as it progresses in its job, and you might
want to use them just for being more careful about what is going on, or
merely for entertaining yourself. If you have encountered a problem
when operating on an archive, however, you may need more information
than just an error message in order to solve the problem. The following
options can be helpful diagnostic tools.
Normally, the '--list' ('-t') command to list an archive prints just
the file names (one per line) and the other commands are silent. When
used with most operations, the '--verbose' ('-v') option causes 'tar' to
print the name of each file or archive member as it is processed. This
and the other options which make 'tar' print status information can be
useful in monitoring 'tar'.
With '--create' or '--extract', '--verbose' used once just prints the
names of the files or members as they are processed. Using it twice
causes 'tar' to print a longer listing (*Note verbose member listing::,
for the description) for each member. Since '--list' already prints the
names of the members, '--verbose' used once with '--list' causes 'tar'
to print an 'ls -l' type listing of the files in the archive. The
following examples both extract members with long list output:
$ tar --extract --file=archive.tar --verbose --verbose
$ tar xvvf archive.tar
Verbose output appears on the standard output except when an archive
is being written to the standard output, as with 'tar --create --file=-
--verbose' ('tar cfv -', or even 'tar cv'--if the installer let standard
output be the default archive). In that case 'tar' writes verbose
output to the standard error stream.
If '--index-file=FILE' is specified, 'tar' sends verbose output to
FILE rather than to standard output or standard error.
The '--totals' option causes 'tar' to print on the standard error the
total amount of bytes transferred when processing an archive. When
creating or appending to an archive, this option prints the number of
bytes written to the archive and the average speed at which they have
been written, e.g.:
$ tar -c -f archive.tar --totals /home
Total bytes written: 7924664320 (7.4GiB, 85MiB/s)
When reading an archive, this option displays the number of bytes
read:
$ tar -x -f archive.tar --totals
Total bytes read: 7924664320 (7.4GiB, 95MiB/s)
Finally, when deleting from an archive, the '--totals' option
displays both numbers plus number of bytes removed from the archive:
$ tar --delete -f foo.tar --totals --wildcards '*~'
Total bytes read: 9543680 (9.2MiB, 201MiB/s)
Total bytes written: 3829760 (3.7MiB, 81MiB/s)
Total bytes deleted: 1474048
You can also obtain this information on request. When '--totals' is
used with an argument, this argument is interpreted as a symbolic name
of a signal, upon delivery of which the statistics is to be printed:
'--totals=SIGNO'
Print statistics upon delivery of signal SIGNO. Valid arguments
are: 'SIGHUP', 'SIGQUIT', 'SIGINT', 'SIGUSR1' and 'SIGUSR2'.
Shortened names without 'SIG' prefix are also accepted.
Both forms of '--totals' option can be used simultaneously. Thus,
'tar -x --totals --totals=USR1' instructs 'tar' to extract all members
from its default archive and print statistics after finishing the
extraction, as well as when receiving signal 'SIGUSR1'.
The '--checkpoint' option prints an occasional message as 'tar' reads
or writes the archive. It is designed for those who don't need the more
detailed (and voluminous) output of '--block-number' ('-R'), but do want
visual confirmation that 'tar' is actually making forward progress. By
default it prints a message each 10 records read or written. This can
be changed by giving it a numeric argument after an equal sign:
$ tar -c --checkpoint=1000 /var
tar: Write checkpoint 1000
tar: Write checkpoint 2000
tar: Write checkpoint 3000
This example shows the default checkpoint message used by 'tar'. If
you place a dot immediately after the equal sign, it will print a '.' at
each checkpoint(1). For example:
$ tar -c --checkpoint=.1000 /var
...
The '--checkpoint' option provides a flexible mechanism for executing
arbitrary actions upon hitting checkpoints, see the next section (*note
checkpoints::), for more information on it.
The '--show-omitted-dirs' option, when reading an archive--with
'--list' or '--extract', for example--causes a message to be printed for
each directory in the archive which is skipped. This happens regardless
of the reason for skipping: the directory might not have been named on
the command line (implicitly or explicitly), it might be excluded by the
use of the '--exclude=PATTERN' option, or some other reason.
If '--block-number' ('-R') is used, 'tar' prints, along with every
message it would normally produce, the block number within the archive
where the message was triggered. Also, supplementary messages are
triggered when reading blocks full of NULs, or when hitting end of file
on the archive. As of now, if the archive is properly terminated with a
NUL block, the reading of the file may stop before end of file is met,
so the position of end of file will not usually show when
'--block-number' ('-R') is used. Note that GNU 'tar' drains the archive
before exiting when reading the archive from a pipe.
This option is especially useful when reading damaged archives, since
it helps pinpoint the damaged sections. It can also be used with
'--list' ('-t') when listing a file-system backup tape, allowing you to
choose among several backup tapes when retrieving a file later, in favor
of the tape where the file appears earliest (closest to the front of the
tape). *Note backup::.
---------- Footnotes ----------
(1) This is actually a shortcut for '--checkpoint=N
--checkpoint-action=dot'. *Note dot: checkpoints.
File: tar.info, Node: checkpoints, Next: warnings, Prev: verbose, Up: tar invocation
3.8 Checkpoints
===============
A "checkpoint" is a moment of time before writing Nth record to the
archive (a "write checkpoint"), or before reading Nth record from the
archive (a "read checkpoint"). Checkpoints allow to periodically
execute arbitrary actions.
The checkpoint facility is enabled using the following option:
'--checkpoint[=N]'
Schedule checkpoints before writing or reading each Nth record.
The default value for N is 10.
A list of arbitrary "actions" can be executed at each checkpoint.
These actions include: pausing, displaying textual messages, and
executing arbitrary external programs. Actions are defined using the
'--checkpoint-action' option.
'--checkpoint-action=ACTION'
Execute an ACTION at each checkpoint.
The simplest value of ACTION is 'echo'. It instructs 'tar' to
display the default message on the standard error stream upon arriving
at each checkpoint. The default message is (in POSIX locale) 'Write
checkpoint N', for write checkpoints, and 'Read checkpoint N', for read
checkpoints. Here, N represents ordinal number of the checkpoint.
In another locales, translated versions of this message are used.
This is the default action, so running:
$ tar -c --checkpoint=1000 --checkpoint-action=echo /var
is equivalent to:
$ tar -c --checkpoint=1000 /var
The 'echo' action also allows to supply a customized message. You do
so by placing an equals sign and the message right after it, e.g.:
--checkpoint-action="echo=Hit %s checkpoint #%u"
The '%s' and '%u' in the above example are "meta-characters". The
'%s' meta-character is replaced with the "type" of the checkpoint:
'write' or 'read' (or a corresponding translated version in locales
other than POSIX). The '%u' meta-character is replaced with the ordinal
number of the checkpoint. Thus, the above example could produce the
following output when used with the '--create' option:
tar: Hit write checkpoint #10
tar: Hit write checkpoint #20
tar: Hit write checkpoint #30
Aside from meta-character expansion, the message string is subject to
"unquoting", during which the backslash "escape sequences" are replaced
with their corresponding ASCII characters (*note escape sequences::).
E.g. the following action will produce an audible bell and the message
described above at each checkpoint:
--checkpoint-action='echo=\aHit %s checkpoint #%u'
There is also a special action which produces an audible signal:
'bell'. It is not equivalent to 'echo='\a'', because 'bell' sends the
bell directly to the console ('/dev/tty'), whereas 'echo='\a'' sends it
to the standard error.
The 'ttyout=STRING' action outputs STRING to '/dev/tty', so it can be
used even if the standard output is redirected elsewhere. The STRING is
subject to the same modifications as with 'echo' action. In contrast to
the latter, 'ttyout' does not prepend 'tar' executable name to the
string, nor does it output a newline after it. For example, the
following action will print the checkpoint message at the same screen
line, overwriting any previous message:
--checkpoint-action="ttyout=\rHit %s checkpoint #%u"
Another available checkpoint action is 'dot' (or '.'). It instructs
'tar' to print a single dot on the standard listing stream, e.g.:
$ tar -c --checkpoint=1000 --checkpoint-action=dot /var
...
For compatibility with previous GNU 'tar' versions, this action can
be abbreviated by placing a dot in front of the checkpoint frequency, as
shown in the previous section.
Yet another action, 'sleep', pauses 'tar' for a specified amount of
seconds. The following example will stop for 30 seconds at each
checkpoint:
$ tar -c --checkpoint=1000 --checkpoint-action=sleep=30
Finally, the 'exec' action executes a given external program. For
example:
$ tar -c --checkpoint=1000 --checkpoint-action=exec=/sbin/cpoint
This program is executed using '/bin/sh -c', with no additional
arguments. Its exit code is ignored. It gets a copy of 'tar''s
environment plus the following variables:
'TAR_VERSION'
GNU 'tar' version number.
'TAR_ARCHIVE'
The name of the archive 'tar' is processing.
'TAR_BLOCKING_FACTOR'
Current blocking factor (*note Blocking::).
'TAR_CHECKPOINT'
Number of the checkpoint.
'TAR_SUBCOMMAND'
A short option describing the operation 'tar' is executing. *Note
Operations::, for a complete list of subcommand options.
'TAR_FORMAT'
Format of the archive being processed. *Note Formats::, for a
complete list of archive format names.
Any number of actions can be defined, by supplying several
'--checkpoint-action' options in the command line. For example, the
command below displays two messages, pauses execution for 30 seconds and
executes the '/sbin/cpoint' script:
$ tar -c -f arc.tar \
--checkpoint-action='\aecho=Hit %s checkpoint #%u' \
--checkpoint-action='echo=Sleeping for 30 seconds' \
--checkpoint-action='sleep=30' \
--checkpoint-action='exec=/sbin/cpoint'
This example also illustrates the fact that '--checkpoint-action' can
be used without '--checkpoint'. In this case, the default checkpoint
frequency (at each 10th record) is assumed.
File: tar.info, Node: warnings, Next: interactive, Prev: checkpoints, Up: tar invocation
3.9 Controlling Warning Messages
================================
Sometimes, while performing the requested task, GNU 'tar' notices some
conditions that are not exactly errors, but which the user should be
aware of. When this happens, 'tar' issues a "warning message"
describing the condition. Warning messages are output to the standard
error and they do not affect the exit code of 'tar' command.
GNU 'tar' allows the user to suppress some or all of its warning
messages:
'--warning=KEYWORD'
Control display of the warning messages identified by KEYWORD. If
KEYWORD starts with the prefix 'no-', such messages are suppressed.
Otherwise, they are enabled.
Multiple '--warning' messages accumulate.
The tables below list allowed values for KEYWORD along with the
warning messages they control.
Keywords controlling 'tar' operation
------------------------------------
all
Enable all warning messages. This is the default.
none
Disable all warning messages.
filename-with-nuls
'%s: file name read contains nul character'
alone-zero-block
'A lone zero block at %s'
Keywords applicable for 'tar --create'
--------------------------------------
cachedir
'%s: contains a cache directory tag %s; %s'
file-shrank
'%s: File shrank by %s bytes; padding with zeros'
xdev
'%s: file is on a different filesystem; not dumped'
file-ignored
'%s: Unknown file type; file ignored'
'%s: socket ignored'
'%s: door ignored'
file-unchanged
'%s: file is unchanged; not dumped'
ignore-archive
'%s: file is the archive; not dumped'
file-removed
'%s: File removed before we read it'
file-changed
'%s: file changed as we read it'
Keywords applicable for 'tar --extract'
---------------------------------------
timestamp
'%s: implausibly old time stamp %s'
'%s: time stamp %s is %s s in the future'
contiguous-cast
'Extracting contiguous files as regular files'
symlink-cast
'Attempting extraction of symbolic links as hard links'
unknown-cast
'%s: Unknown file type `%c', extracted as normal file'
ignore-newer
'Current %s is newer or same age'
unknown-keyword
'Ignoring unknown extended header keyword `%s''
decompress-program
Controls verbose description of failures occurring when trying to
run alternative decompressor programs (*note alternative
decompression programs::). This warning is disabled by default
(unless '--verbose' is used). A common example of what you can get
when using this warning is:
$ tar --warning=decompress-program -x -f archive.Z
tar (child): cannot run compress: No such file or directory
tar (child): trying gzip
This means that 'tar' first tried to decompress 'archive.Z' using
'compress', and, when that failed, switched to 'gzip'.
xattr-write
'%s: Cannot set '%s' extended attribute for file '%s''
'%s: Cannot set POSIX ACLs for file '%s''
'%s: Cannot set SELinux context for file '%s''
Keywords controlling incremental extraction:
--------------------------------------------
rename-directory
'%s: Directory has been renamed from %s'
'%s: Directory has been renamed'
new-directory
'%s: Directory is new'
xdev
'%s: directory is on a different device: not purging'
bad-dumpdir
'Malformed dumpdir: 'X' never used'
File: tar.info, Node: interactive, Prev: warnings, Up: tar invocation
3.10 Asking for Confirmation During Operations
==============================================
Typically, 'tar' carries out a command without stopping for further
instructions. In some situations however, you may want to exclude some
files and archive members from the operation (for instance if disk or
storage space is tight). You can do this by excluding certain files
automatically (*note Choosing::), or by performing an operation
interactively, using the '--interactive' ('-w') option. 'tar' also
accepts '--confirmation' for this option.
When the '--interactive' ('-w') option is specified, before reading,
writing, or deleting files, 'tar' first prints a message for each such
file, telling what operation it intends to take, then asks for
confirmation on the terminal. The actions which require confirmation
include adding a file to the archive, extracting a file from the
archive, deleting a file from the archive, and deleting a file from
disk. To confirm the action, you must type a line of input beginning
with 'y'. If your input line begins with anything other than 'y', 'tar'
skips that file.
If 'tar' is reading the archive from the standard input, 'tar' opens
the file '/dev/tty' to support the interactive communications.
Verbose output is normally sent to standard output, separate from
other error messages. However, if the archive is produced directly on
standard output, then verbose output is mixed with errors on 'stderr'.
Producing the archive on standard output may be used as a way to avoid
using disk space, when the archive is soon to be consumed by another
process reading it, say. Some people felt the need of producing an
archive on stdout, still willing to segregate between verbose output and
error output. A possible approach would be using a named pipe to
receive the archive, and having the consumer process to read from that
named pipe. This has the advantage of letting standard output free to
receive verbose output, all separate from errors.
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