tar -- USTAR-compatible tape archiver to copy and back up files

tar USTAR-compatible tape archiver to copy and back up files	Command

SYNOPSIS

tar -c[#sbfNvwlzU] [blocking_factor] [archivefile] [-V volpat] [file...] [-C pathname] [file...]

tar -r[#sbfNvwlzU] [blocking_factor] [archivefile] [-V volpat] [file...] [-C pathname] [file...]

tar -t[#sbfNvzU] [blocking_factor] [archivefile] [-V volpat] [file ...]

tar -x[#sbfNvwpmozU] [blocking_factor] [archivefile] [-V volpat] [file ...]

tar manipulates archives. An archive is a single file that contains the complete contents of a set of other files; an archive preserves the directory hierarchy that contained the original files, in a manner similar to cpio. The name tar was derived from Tape ARchiver; however, you can use archives with any medium, including diskettes.

This version of the tar utility writes and reads the original tar format from UNIX systems as well as the USTAR format defined by the POSIX (IEEE P1003.1) standards group.

Primary Options

The four forms of the command shown in the synopsis represent the main functions of tar. You must specify one of these primary options as the first character of an option string.

-c: creates an archive. This command writes each named file into a newly-created archive. Directories recursively include all components. If - appears in place of any file name, tar reads the standard input for a list of files, one per line. This allows other commands to generate lists of files for tar to archive.
-r: writes the named files to the end of the archive. It is possible to have more than one copy of a file in an archive using this method. To use this form of the command with a tape, it must be possible to backspace the tape.
-t: displays a table of contents. This display contains the names of all the files in the archive, one per line. If you specify one or more files on the command line, tar prints only those file names. Under the verbose (-v) option, more information about each archive member is printed, in a format similar to that produced by ls -l.
-x: extracts files from an archive. tar extracts each named file to a file of the same name. If you do not specify any files on the command line, tar extracts all files in the archive. This extraction restores all file system attributes as controlled by other options.

Secondary Options

Unlike other commands, you must give secondary options to tar as a single string. For example, you might use -tv, but not separate them as in -t -v. You may omit the leading dash - if you want. The only exceptions to the single string rule for secondary options to tar are -C and -V; see below for a full explanation of the secondary options.

-b

sets the number of blocks used for tape archive read/write operations to blocking_factor. If you specify -b, you must specify a blocking_factor argument. When reading from the tape archive, tar automatically determines the blocking factor by trying to read the largest legal blocking factor and using the actual number read to be the blocking_factor. For UNIX compatibility, the largest valid value for blocking_factor is 20 blocks; in USTAR mode, it is 60 blocks. If -b comes before -f in the options string, the blocking_factor must come before the filename. Note that blocks are typically 512 bytes, although some tape drives support other sizes.

-C pathname

is an unusual option because it is specified in the middle of your file list. When tar encounters a -C pathname option while archiving files, tar treats pathname as the current directory and treats all following entries in your file list (including another -C) as being relative to pathname.

-f

uses the archivefile for the tape archive rather than the default device. If -f is used, the archivefile argument must be specified. If -f comes before -b in the options string, the archivefile must come before the blocking_factor. If archivefile is the character -, tar uses the standard input for reading and the standard output for writing archives.

#s

sets the default archive file name to a specific tape unit number and density. For a more general method, use the -f option. The # may be any digit between 0 and 7, inclusive, to select the tape unit. The density selector s may be l(low), m(medium), or h(high). For finer control over the density, use the -f or -V option with an archive name such as -f /dev/nmtdqic-150; see tape for information on SCSI tape device names.

-l

complains if all links are not resolved when adding files to the tape archive.

-m

does not restore a file's modification time stamp when extracting it from an archive. By default, tar restores the time stamp from information contained in the archive.

-o

when extracting files, does not attempt to assign owner and group information to extracted files. With this option, most operating systems assign your owner and group information to extracted files by default.

-p

when extracting, preserves the three high-order file attribute bits, exactly as in the archive. On UNIX and POSIX-compliant systems, they indicate the set-user-ID, set-group-ID, and saved-text attributes; to use -p on these systems, you must have appropriate privileges. When -p is set, tar ignores the UMASK and restores the modes exactly as in the archive.

-U

when creating a new tape archive with the -c option, forces tar to use the USTAR format. The default format used when creating a new archive is the original UNIX tar format. When you do not specify -c, tar determines whether or not the tape archive is in USTAR format by reading it, so the U option does not affect file extraction. tar displays an error message for a UNIX tar format file containing a bad file name; -U suppresses this message and still extracts the data if the file name is acceptable in USTAR format.

-v

displays each file name, along with the appropriate action key letter (a for add, x for extract) as it processes the archive. With the -t form of the command, this option gives more detail about each archive member being listed.

-V volpat

provides automatic multi-volume support. tar writes output to files -- whose names are formatted using volpat. Any occurrence of # in volpat is replaced by the current volume number. When you invoke tar with this option, it asks you to insert the appropriate disk and then hit return before it proceeds with the operation. With this option set, tar issues the same sort of message when a write error or read error occurs on the archive. The reasoning is that this kind of error means that tar has reached the end of the volume and should go on to a new one.

-w

is used to confirm each operation, such as replacing or extracting. tar displays the operation and the file involved. You can then confirm whether or not you want the operation to take place. Typing in an affirmative answer (in the POSIX locale, one that begins with y or Y) tells tar to do the operation; anything else tells tar to go on to the next operation.

-z

performs compression. Output is at compression level 5. On input, any compression level up to 9 is acceptable. In addition, -z expands compressed archives on input.

tar uses the gzip format to compress files.

EXAMPLES

The compression option provides a more efficient way of expressing:

tar -cvf - directory | mkszip >archive

as the one command line:

tar -cvzf archive directory

To identify all files that have been changed in the last week (7 days), and to archive them to a file on diskette, you might type:

find directory -mtime -7 | tar -cvf a:archive -

DIAGNOSTICS

Possible exit status values:

0

Successful completion.

1

Failure due to any of the following:

— invalid option

— invalid command line arguments

— out of memory

— compression error

— failure on extraction

— failure on creation

PORTABILITY

x/OPEN Portability Guide 4.0.

We strongly recommend, however, that you specify tape devices as described under tape in the MKS Toolkit Reference Manual. For example

/dev/mt0

The -U option is an extension to provide POSIX USTAR format compatibility.

The -p option is a common extension on BSD UNIX systems that is not available on UNIX System V systems.

These two options as well as the -C, -V, and -z options are extensions to the x/OPEN standard. The -u option specified in XPG is not currently supported.

LIMITS

Path names in the tape archive are normally restricted to a maximum length of 100 bytes. However, in USTAR mode, path names may be up to 255 bytes long.

A description of the tape archive format is found in the tar file format reference page.

NOTES

The tar utility cannot save files larger than eight gigabytes in size in an archive. However, other programs that extract files from tar archives may be unable to properly extract files larger than two gigabytes and tar issues a warning to that effect when you attempt to save such a file.

tar

Command