The function portion of the key is specified by one of the following letters:

c

Create. Writing begins at the beginning of the tarfile, instead of at the end.

r

Replace. The named files are written at the end of the tarfile. A file created with extended headers must be updated with extended headers (see E flag under Function Modifiers). A file created without extended headers cannot be modified with extended headers.

t

Table of Contents. The names of the specified files are listed each time they occur in the tarfile. If no file argument is given, the names of all files and any associated extended attributes in the tarfile are listed. With the v function modifier, additional information for the specified files is displayed.

u

Update. The named files are written at the end of the tarfile if they are not already in the tarfile, or if they have been modified since last written to that tarfile. An update can be rather slow. A tarfile created on a 5.x system cannot be updated on a 4.x system. A file created with extended headers must be updated with extended headers (see E flag under Function Modifiers). A file created without extended headers cannot be modified with extended headers.

x

Extract or restore. The named files are extracted from the tarfile and written to the directory specified in the tarfile, relative to the current directory. Use the relative path names of files and directories to be extracted.

Absolute path names contained in the tar archive are unpacked using the absolute path names, that is, the leading forward slash (/) is not stripped off.

If a named file matches a directory whose contents has been written to the tarfile, this directory is recursively extracted. The owner, modification time, and mode are restored (if possible); otherwise, to restore owner, you must be the super-user. Character-special and block-special devices (created by mknod(1M)) can only be extracted by the super-user. If no file argument is given, the entire content of the tarfile is extracted. If the tarfile contains several files with the same name, each file is written to the appropriate directory, overwriting the previous one. Filename substitution wildcards cannot be used for extracting files from the archive. Rather, use a command of the form:

tar xvf ... /dev/rmt/0 `tar tf ... /dev/rmt/0 | \ grep 'pattern' `

When extracting tapes created with the r or u functions, directory modification times may not be set correctly. These same functions cannot be used with many tape drives due to tape drive limitations such as the absence of backspace or append capabilities.

When using the r, u, or x functions or the X function modifier, the named files must match exactly the corresponding files in the tarfile. For example, to extract ./thisfile, you must specify ./thisfile, and not thisfile. The t function displays how each file was archived.

The characters below may be used in conjunction with the letter that selects the desired function.

b

Blocking Factor. Use when reading or writing to raw magnetic archives (see f below). The block argument specifies the number of 512-byte tape blocks to be included in each read or write operation performed on the tarfile. The minimum is 1, the default is 20. The maximum value is a function of the amount of memory available and the blocking requirements of the specific tape device involved (see mtio(7I) for details.) The maximum cannot exceed INT_MAX/512 (4194303).

When a tape archive is being read, its actual blocking factor will be automatically detected, provided that it is less than or equal to the nominal blocking factor (the value of the block argument, or the default value if the b modifier is not specified). If the actual blocking factor is greater than the nominal blocking factor, a read error will result. See Example 5 in EXAMPLES.

B

Block. Force tar to perform multiple reads (if necessary) to read exactly enough bytes to fill a block. This function modifier enables tar to work across the Ethernet, since pipes and sockets return partial blocks even when more data is coming. When reading from standard input, '-', this function modifier is selected by default to ensure that tar can recover from short reads.

e

Error. Exit immediately with a positive exit status if any unexpected errors occur. The SYSV3 environment variable overrides the default behavior. (See ENVIRONMENT VARIABLES section below.)

E

Write a tarfile with extended headers. (Used with c, r, or u options; ignored with t or x options.) When a tarfile is written with extended headers, the modification time is maintained with a granularity of microseconds rather than seconds. In addition, filenames no longer than PATH_MAX characters that could not be archived without E, and file sizes greater than 8GB, are supported. The E flag is required whenever the larger files and/or files with longer names, or whose UID/GID exceed 2097151, are to be archived, or if time granularity of microseconds is desired.

f

File. Use the tarfile argument as the name of the tarfile. If f is specified, /etc/default/tar is not searched. If f is omitted, tar will use the device indicated by the TAPE environment variable, if set; otherwise, it will use the default values defined in /etc/default/tar. The number matching the archiveN string is used as the output device with the blocking and size specifications from the file. For example,

tar -c 2/tmp/*

writes the output to the device specified as archive2 in /etc/default/tar.

If the name of the tarfile is '-', tar writes to the standard output or reads from the standard input, whichever is appropriate. tar can be used as the head or tail of a pipeline. tar can also be used to move hierarchies with the command:

example% cd fromdir; tar cf - .| (cd todir; tar xfBp -)

F

With one F argument, tar excludes all directories named SCCS and RCS from the tarfile. With two arguments, FF, tar excludes all directories named SCCS and RCS, all files with .o as their suffix, and all files named errs, core, and a.out. The SYSV3 environment variable overrides the default behavior. (See ENVIRONMENT VARIABLES section below.)

h

Follow symbolic links as if they were normal files or directories. Normally, tar does not follow symbolic links.

i

Ignore directory checksum errors.

k size

Requires tar to use the size argument as the size of an archive in kilobytes. This is useful when the archive is intended for a fixed size device such as floppy disks. Large files are then split across volumes if they do not fit in the specified size.

l

Link. Output error message if unable to resolve all links to the files being archived. If l is not specified, no error messages are printed.

m

Modify. The modification time of the file is the time of extraction. This function modifier is valid only with the x function.

n

The file being read is a non-tape device. Reading of the archive is faster since tar can randomly seek around the archive.

o

Ownership. Assign to extracted files the user and group identifiers of the user running the program, rather than those on tarfile. This is the default behavior for users other than root. If the o function modifier is not set and the user is root, the extracted files will take on the group and user identifiers of the files on tarfile (see chown(1) for more information). The o function modifier is only valid with the x function.

p

Restore the named files to their original modes, and ACLs if applicable, ignoring the present umask(1). This is the default behavior if invoked as super-user with the x function letter specified. If super-user, SETUID, and sticky information are also extracted, and files are restored with their original owners and permissions, rather than owned by root. When this function modifier is used with the c function, ACLs are created in the tarfile along with other information. Errors will occur when a tarfile with ACLs is extracted by previous versions of tar.

P

Suppress the addition of a trailing "/" on directory entries in the archive.

q

Stop after extracting the first occurrence of the named file. tar will normally continue reading the archive after finding an occurrence of a file.

v

Verbose. Output the name of each file preceded by the function letter. With the t function, v provides additional information about the tarfile entries. The listing is similar to the format produced by the -l option of the ls(1) command.

w

What. Output the action to be taken and the name of the file, then await the user's confirmation. If the response is affirmative, the action is performed; otherwise, the action is not performed. This function modifier cannot be used with the t function.

X

Exclude. Use the exclude-file argument as a file containing a list of relative path names for files (or directories) to be excluded from the tarfile when using the functions c, x, or t. Be careful of trailing white spaces. Also beware of leading white spaces, since, for each line in the excluded file, the entire line (apart from the newline) will be used to match against the initial string of files to exclude. Multiple X arguments may be used, with one exclude-file per argument. In the case where included files (see -I include-file option) are also specified, the excluded files take precedence over all included files. If a file is specified in both the exclude-file and the include-file (or on the command line), it will be excluded.

@

Include extended attributes in archive. By default, tar does not place extended attributes in the archive. With this flag, tar will look for extended attributes on the files to be placed in the archive and add them to the archive. Extended attributes go in the archive as special files with a special type label. When this modifier is used with the x function, extended attributes are extracted from the tape along with the normal file data. Extended attribute files can only be extracted from an archive as part of a normal file extract. Attempts to explicitly extract attribute records are ignored.

[0-7]

Select an alternative drive on which the tape is mounted. The default entries are specified in /etc/default/tar. If no digit or f function modifier is specified, the entry in /etc/default/tar with digit "0" is the default.

The following is an example using tar to create an archive of your home directory on a tape mounted on drive /dev/rmt/0:

example% cd
example% tar cvf /dev/rmt/0 .
messages from tar 

The c function letter means create the archive. The v function modifier outputs messages explaining what tar is doing. The f function modifier indicates that the tarfile is being specified (/dev/rmt/0 in this example). The dot (.) at the end of the command line indicates the current directory and is the argument of the f function modifier.

Display the table of contents of the tarfile with the following command:

example% tar tvf /dev/rmt/0

The output will be similar to the following for the POSIX locale:

rw-r--r--   1677/40    2123    Nov  7 18:15 1985    ./test.c
...
example%

The columns have the following meanings:

• column 1 is the access permissions to ./test.c
• column 2 is the user-id/group-id of ./test.c
• column 3 is the size of ./test.c in bytes
• column 4 is the modification date of ./test.c. When the LC_TIME category is not set to the POSIX locale, a different format and date order field may be used.
• column 5 is the name of ./test.c

To extract files from the archive:

example% tar xvf /dev/rmt/0
messages from tar
example%

If there are multiple archive files on a tape, each is separated from the following one by an EOF marker. To have tar read the first and second archives from a tape with multiple archives on it, the non-rewinding version of the tape device name must be used with the f function modifier, as follows:

example% tar xvfp /dev/rmt/0n read first archive from tape
messages from tar
example% tar xvfp /dev/rmt/0n read second archive from tape
messages from tar
example%

Notice that in some earlier releases, the above scenario did not work correctly, and intervention with mt(1) between tar invocations was necessary. To emulate the old behavior, use the non-rewind device name containing the letter b for BSD behavior. See the Close Operations section of the mtio(7I) manual page.

To archive files from /usr/include and from /etc to default tape drive 0:

example% tar c -C /usr  include -C /etc .

The table of contents from the resulting tarfile would produce output like the following:

include/ 
include/a.out.h
and all the other files in /usr/include ...
./chown and all the other files in /etc 

To extract all files in the include directory:

example% tar xv include
x include/, 0 bytes, 0 tape blocks \ 
    and all files under include ...

The following is an example using tar to transfer files across the network. First, here is how to archive files from the local machine (example) to a tape on a remote system (host):

example% tar cvfb - 20 files | \
    rsh host dd of=/dev/rmt/0  obs=20b
messages from tar
example%

In the example above, we are creating a tarfile with the c key letter, asking for verbose output from tar with the v function modifier, specifying the name of the output tarfile using the f function modifier (the standard output is where the tarfile appears, as indicated by the `-' sign), and specifying the blocksize (20) with the b function modifier. If you want to change the blocksize, you must change the blocksize arguments both on the tar command and on the dd command.

The following is an example that uses tar to retrieve files from a tape on the remote system back to the local system:

example% rsh -n host dd if=/dev/rmt/0 bs=20b | \
    tar xvBfb - 20 files
messages from tar
example%

In the example above, we are extracting from the tarfile with the x key letter, asking for verbose output from tar with the v function modifier, telling tar it is reading from a pipe with the B function modifier, specifying the name of the input tarfile using the f function modifier (the standard input is where the tarfile appears, as indicated by the `-' sign), and specifying the blocksize (20) with the b function modifier.

The following example creates an archive of the home directory on /dev/rmt/0 with an actual blocking factor of 19:

example% tar cvfb /dev/rmt/0 19 $HOME

To recognize this archive's actual blocking factor without using the b function modifier:

example% tar tvf /dev/rmt/0
tar: blocksize = 19
...

To recognize this archive's actual blocking factor using a larger nominal blocking factor:

example% tar tvf /dev/rmt/0 30
tar: blocksize = 19
...

Attempt to recognize this archive's actual blocking factor using a nominal blocking factor that is too small:

example% tar tvf /dev/rmt/0 10
tar: tape read error