TAR(C) UNIX System V
Name
tar - archives files
Syntax
tar [ key ] [ files ]
Description
tar saves and restores files to and from an archive medium,
which is typically a storage device such as floppy disk or
tape, or a regular file. Its actions are controlled by the
key argument. The key is a string of characters containing
at most one function letter and possibly one or more
function modifiers. Valid function letters are c, t, x, and
e. Other arguments to the command are files (or directory
names) specifying which files are to be backed up or
restored. In all cases, appearance of a directory name
refers to the files and (recursively) subdirectories of that
directory. The r and u option cannot be used with tape
devices.
The function portion of the key is specified by one of the
following letters:
r The named files are written to the end of an
existing archive.
x The named files are extracted from the archive. If
a named file matches a directory whose contents had
been written onto the archive, this directory is
(recursively) extracted. The owner, modification
time, and mode are restored (if possible). If no
files argument is given, the entire contents of the
archive are extracted. Note that if several files
with the same name are on the archive, the last one
overwrites all earlier ones.
t The names of the specified files are listed each
time that they occur on the archive. If no files
argument is given, all the names on the archive are
listed.
u The named files are added to the archive if they are
not already there, or if they have been modified
since last written on that archive.
c Creates a new archive; writing begins at the
beginning of the archive, instead of after the last
file.
The following characters may be used in addition to the
letter that selects the desired function:
0,...,9999
This modifier selects the drive on which the archive
is mounted. The default is found in the file
/etc/default/tar.
v Normally, tar does its work silently. The v
(verbose) option causes it to display the name of
each file it treats, preceded by the function
letter. With the t function, v gives more
information about the archive entries than just the
name.
w Causes tar to display the action to be taken,
followed by the name of the file, and then wait for
the user's confirmation. If a word beginning with y
is given, the action is performed. Any other input
means ``no''.
f Causes tar to use the next argument as the name of
the archive instead of the default device listed in
/etc/default/tar. If the name of the file is a dash
(-), tar writes to the standard output or reads from
the standard input, whichever is appropriate. Thus,
tar can be used as the head or tail of a pipeline.
tar can also be used to move hierarchies with the
command:
cd fromdir; tar cf - . | (cd todir; tar xf -)
b Causes tar to use the next argument as the blocking
factor for archive records. The default is 1, the
maximum is 20. This option should only be used with
raw magnetic tape archives (see f above). The block
size is determined automatically when reading tapes
(key letters x and t).
F Causes tar to use the next argument as the name of a
file from which succeeding arguments are taken.
l Tells tar to display an error message if it cannot
resolve all of the links to the files being backed
up. If l is not specified, no error messages are
displayed.
m Tells tar to not restore the modification times.
The modification time of the file is the time of
extraction.
k Causes tar to use the next argument as the size of
an archive volume in kilobytes. The minimum value
allowed is 250. Very large files are split into
``extents'' across volumes. When restoring from a
multivolume archive, tar only prompts for a new
volume if a split file has been partially restored.
To override the value of k in the default file,
specify k as 0 on the command line.
e Prevents files from being split across volumes
(tapes or floppy disks). If there is not enough
room on the present volume for a given file, tar
prompts for a new volume. This is only valid when
the k option is also specified on the command line.
n Indicates the archive device is not a magnetic tape.
The k option implies this. Listing and extracting
the contents of an archive are sped because tar can
seek over files it wishes to skip. Sizes are
printed in kilobytes instead of tape blocks.
p Indicates that files are extracted using their
original permissions. It is possible that a non-
super-user may be unable to extract files because of
the permissions associated with the files or
directories being extracted.
A Suppresses absolute filenames. Any leading
``/''characters are removed from filenames. During
extraction arguments given should match the relative
(rather than the absolute) pathnames. With the c,
r, u options the A options can be used to inhibit
putting leading slashes in the archive headers.
tar reads /etc/default/tar to obtain default values for the
device, blocking factor, volume size, and the device type
(tape or non-tape). If no numeric key is specified on the
command, tar looks for a line in the default file beginning
with the string archive=. Following this pattern are 4
blank separated strings indicating the values for the
device, blocking factor, volume size and device type, in
that order. A volume size of `0' indicates infinite volume
length. This entry should be modified to reflect the size
of the tape volumes used.
For example, the following is the default device entry from
/etc/default/tar :
archive=/dev/fd096ds15 10 1200 n
The n in the last field, means that this device is not a
tape. Use y for tape devices. Any default value may be
overridden on the command line. The numeric keys (0-7)
select the line from the default value beginning with
archive#=, where # is the numeric key. When the f key
letter is specified on the command line, the entry
"archivef=" is used. In this case, the default file entry
must still contain 4 strings, but the first entry
(specifying the device) is not significant. The default
file /etc/default/tar need not exist if a device is
specified on the command line.
Notes
A critical consideration when creating a tar volume involves
the use of absolute or relative pathnames. Consider the
following tar command examples, as executed from the
directory /u/target:
tar cv /u/target/arrow
tar cv arrow
The first command creates a tar volume with the absolute
pathname: /u/target/arrow. The second yields a tar volume
with a relative pathname: ./arrow. (The ./ is implicit and
shown here as an example, ./ should not be specified when
retrieving the file from the archive.) When restored, the
first example results in the file arrow being written to the
directory /u/target (if it exists and you have write
permission) no matter what your working directory. The
second example simple writes the file arrow to your present
working directory.
Absolute pathnames specify the location of a file in
relation to the root directory (/); relative pathnames are
relative to the current directory. This must be taken into
account when making a tar tape or disk. Backup volumes use
absolute pathnames so that they can be restored to the
proper directory. Use relative pathnames when creating a
tar volume where absolute pathnames are unnecessary.
Examples
If the name of a floppy disk device is /dev/fd1, then a tar
format file can be created on this device by entering:
assign /dev/fd
tar cvfk /dev/fd1 360 files
where files are the names of files you want archived and 360
is the capacity of the floppy disk in kilobytes. Note that
arguments to key letters are given in the same order as the
key letters themselves, thus the fk key letters have
corresponding arguments /dev/fd1 and 360. Note that if a
file is a directory, the contents of the directory are
recursively archived. To display a listing of the archive,
enter:
tar tvf /dev/fd1
At some later time you will likely want to extract the files
from the archive floppy. You can do this by entering:
tar xvf /dev/fd1
The above command extracts all files from the archive, using
the exact same pathnames as used when the archive was
created. Because of this behavior, it is normally best to
save archive files with relative pathnames rather than
absolute ones, since directory permissions may not let you
read the files into the absolute directories specified.
(See the A flag under Options.)
In the above examples, the v verbose option is used simply
to confirm the reading or writing of archive files on the
screen. Also, a normal file could be substituted for the
floppy device /dev/fd1 shown in the examples.
Files
/etc/default/tar Default devices, blocking and
volume sizes, device type
/tmp/tar*
Diagnostics
Displays an error message about bad key characters and
archive read/write errors.
Displays an error message if not enough memory is available
to hold the link tables.
Notes
There is no way to ask for the nth occurrence of a file.
tar does not verify the selected media type.
The u option can be slow.
The limit on filename length is 100 characters.
When archiving a directory that contains subdirectories, tar
will only access those subdirectories that are within 17
levels of nesting. Subdirectories at higher levels will be
ignored after tar displays an error message.
When using tar with a raw device, specify the block size
with the b option as a multiple of 1K. For example, to use
a 9K block size, enter:
tar cvfb /dev/rfd0 18 file
Do not enter:
tar xfF - -
This would imply taking two things from the standard input
at the same time.
Use error-free floppy disks for best results with tar.
Standards Conformance
tar is conformant with:
AT&T SVID Issue 2, Select Code 307-127;
and The X/Open Portability Guide II of January 1987.
(printed 2/15/90) TAR(C)