Content-type: text/html Man page of tar

tar

Section: User Commands (1)
Index Return to Main Contents
 

NAME

tar - Manipulates tape archives  

SYNOPSIS

tar function_key[bBfFEhilLmpPsSvVwzn] [n|o] [option_argument...] [-e exception]... [-C directory]... [file...]

tar -function_key[options] [option_argument]... [n|o] [option_argument...] [-e exception]... [-C directory]... [file...]

The tar command saves and restores multiple files on a single file (usually a magnetic tape, but it can be any file).

Note

[Compaq]  The syntax of the tar command has recently changed. The minus sign (-) at the beginning of a key/option set is no longer optional. If tar sees a minus sign in front of an option that requires an argument, tar expects the argument to follow the option immediately. In order to use the original tar syntax in existing scripts, you must remove the minus sign if more than one option requiring an argument is given. Consider this command in the old form: tar -xbfp 20 /dev/rmt1h

Under the new implementation, this command becomes tar xbfp 20 /dev/rmt1h

or tar -xb 20 -f /dev/rmt1h -p


 

STANDARDS

Interfaces documented on this reference page conform to industry standards as follows:

tar:  XPG4, XPG4-UNIX

Refer to the standards(5) reference page for more information about industry standards and associated tags.
 

FUNCTION KEYS

[Compaq]  The function performed by tar is specified by one of the following key letters: Creates a new archive. When writing to a tape device, tar begins from the current tape position. Writes the named files at the end of the specified archive. If the archive is on tape, tar expects that the tape is currently positioned to the beginning of the archive. Lists the contents of the archive. If the file argument does not restrict the operation to one or more specific directories or files, tar lists all of the file names in the archive. Adds the named files to the tape, if the files are not already there or if they were modified since last copied to the tape. Extracts the named files from the tape. If a named file matches a directory whose contents were written to the tape, this directory is (recursively) extracted. The owner, modification time, and mode are restored (if possible). If no file argument is given, the entire content of the tape is extracted. If multiple entries specifying the same file are on the tape, the last one overwrites all earlier ones.
 

OPTIONS

[Compaq]  The following options can be used with function keys: The tar command uses the next argument as the blocking factor for tape records. The default is 20 (larger values can be specified at the risk of creating a tape archive that some systems' tape drives might not be able to restore). Use this option only with raw magnetic tape archives. The block size is determined automatically when reading tapes (key letters x and t). [Compaq]  Forces input and output blocking to the blocking factor (see the b option). The B option exists so that tar can work across a communications channel where the blocking cannot be maintained. [Compaq]  The tar command uses the next argument, exception, as the name of the file to be excluded from the archive. Processes extended headers, allowing you to archive or extract extended UIDs and GIDs, long filenames, link-names, large files, and long user and group names The tar command uses the next argument as the name of the archive instead of /dev/rmtnh. (See the entry for the n option.) If the name of the file is - (dash), tar writes to standard output or reads from standard input, whichever is appropriate. Thus, tar can be used as the head or tail of a filter chain. The tar utility can also be used to move hierarchies with the command: cd fromdir; tar cf - . | (cd todir; tar xpf -) [Compaq]  Checks certain file names before archiving. Source Code Control System (SCCS), Revision Control System (RCS), files named core, errs, a.out, and files ending in .o are not archived. [Compaq]  Forces tar to follow symbolic links as if they were normal files or directories. Normally, tar does not follow symbolic links, but instead saves the link text in the archive. [Compaq]  Ignores checksum errors. The tar command writes a file header containing a checksum for each file in the archive. When this option is not specified, the system verifies the contents of the header blocks by recomputing the checksum and stops with a directory checksum error when a mismatch occurs. When this option is specified, tar logs the error and then scans forward until it finds a valid header block. This permits restoring files from later volumes of a multivolume archive without reading earlier volumes. [Compaq]  Tells tar to complain if it cannot resolve all of the links to the files dumped. If this option is not specified, no error messages are printed. [Compaq]  Tries to create a symbolic link if tar is unsuccessful in its attempt to link (hard link) two files. Tells tar not to restore the modification times. The modification time is the time of extraction. This is always the case with symbolic links. [Compaq]  Allows tar headers to be created with file names that cannot be null-terminated if they are exactly the maximum length (as specified in POSIX). This option is mutually exclusive with the o option (that is, new versus old). When specified, each of these options turns off the other; neither option is turned on by default, however. The o option is provided for backward compatibility. Specify this option if the archive is to be restored on a system with an older version of tar. On output, tar normally places information specifying owner and modes of directories in the archive. Former versions of tar, when encountering this information will give an error message of the following form: name: cannot create

[Compaq]  This option suppresses the directory information. It also prevents archiving special files and FIFOs that earlier versions of tar would not be able to extract properly. (Although anyone can archive special files, who has superuser authority can extract them from the archives.)
When o is used for reading, it causes the extracted file to take on the User and Group ID (UID and GID) of the user running the program, rather than those of the tape. This is the default for the ordinary user.
[Compaq]  This option is mutually exclusive with the n option (that is, new vs. old). When specified, each of these options turns off the other; neither option is turned on by default, however. [Compaq]  Restores files to their original modes, ignoring the present umask. Set-user-ID and sticky information will also be restored if the user is superuser. [Compaq]  Specifies the prefix that is to be stripped off of the file names archived to or extracted from tape. (See also the s option.) [Compaq]  Tells tar to strip off any leading slashes from pathnames during extraction. This is useful when restoring a tape that was created on a system with a different file system structure. (See also the P option.) [Compaq]  The named file immediately following this option contains a list of file names separated by newlines. This list is added to (c function key, r function key) or extracted from (x function key) the archive. The -R option is incompatible with the -C option. [Compaq]  Specifies the number of 512-byte blocks per volume (first form), independent of the tape blocking factor. You can also specify the size of the tape in feet, and optionally density, by using the second form. Feet are assumed to be 11 inches long to be conservative. This option lets you deal more easily with multivolume tape archives, where tar must be able to determine how many blocks fit on each volume.
[Compaq]  Tape drives vary in density capabilities. The density argument is used in the amount of data that tar can fit on a tape. Normally tar does its work silently. The v (verbose) option makes tar print the name of each file it processes as specified by the function key. With the t function key, the verbose option gives more information about the tape entries than just their names. [Compaq]  Prevents any extended attributes from being archived with associated files. This option is particularly useful for archiving files that are to be restored with previous versions of tar and cpio. Causes tar to print the action to be taken followed by the name of the file, and then to wait for the user's confirmation. If a word beginning with y, or the locale's definition of an affirmative response, is given, the action is performed. If any other input is given, the action is not performed. [Compaq]  Positions the tape after the EOF marker on extraction or listing. The z option lets the user extract or list tapes that have multiple archives on them one after the other without error as a result of the tape not being positioned correctly for the next extraction or listing. [Compaq]  Selects /dev/rmtnh (the variable n means 0-9) as the tape drive on which the tape is mounted. The default is drive 0 (/dev/rmt0h). [Compaq]  Adds the following argument to a list of exception strings that prevent files whose names match exactly from being archived. When used with the -C option, the list of exceptions becomes relative to each new directory. [Compaq]  If a file name is preceded by -C, tar performs a chdir() to that file name. This allows multiple directories not related by a close common parent to be archived using short relative pathnames. For example, to archive files from /usr/include and from /etc, one might use the following command line: tar c -C /usr/include . -C /etc .
[Compaq]  Therefore, if you do not specify an absolute file name, the file name is considered relative to the previous -C directory. When you specify this option multiple times on the command line, make sure to specify subsequent -C directories relative to the preceding -C directories.
[Compaq]  If an error occurs while trying to change to the requested directory, subsequent file names on the command line that are not absolute (that is, have no leading / (slash)) are skipped until the next -C option is specified.

[Compaq]  Only the -e and -C options must be preceded by a - (dash) and can be specified more than once on a single command line or interspersed within the list of file names. All other options must be specified together (with no separating spaces) before -e, -C, and the file list. For all options that require arguments, the arguments must follow the string of options and be ordered in the same way as the specified options.

[Compaq]  Previous restrictions on the tar command's ability to properly handle blocked archives have been lifted.
 

DESCRIPTION

The tar command is used to save and restore data from traditional format tar archives.

The actions of the tar command are controlled by a string containing, at most, one function key and possibly one or more options. Other arguments to tar are file or directory names specifying which files to dump or restore. In all cases, appearance of a directory name refers to the files and (recursively) subdirectories of that directory.

The LC_MESSAGES variable determines the locale's equivalent of y or n (for yes/no responses).
 

NOTES

[Compaq]  There is no way to ask for the nth occurrence of a file. [Compaq]  Tape errors are handled ungracefully. [Compaq]  The u function can be slow. [Compaq]  The current limit on file name length is 256 bytes. The current limit on file links (hard or soft) is 100 bytes. [Compaq]  There is no way selectively to follow symbolic links. [Compaq]  When extracting tapes created with the r or u functions, directory modification times might not be set correctly. [Compaq]  After encountering tape write errors, tar queries the operator about performing a rewrite. If the operator requests a rewrite, a rewind is performed, followed by an attempt to rewrite the data. In the event the no-rewind device is used, the user should always load a new tape to avoid the possibility of overwriting previously written archives.
 

EXIT STATUS

The following exit values are returned: Successful completion. An error occurred.
 

EXAMPLES

To create a tar archive to device /dev/rmt12, enter: tar cvfb /dev/rmt12 20 -e ./foo -C /usr/glenn . \ -e ./bar -e ./logs/logfile -C /usr/gaston .

The preceding command line specifies a blocking factor of 20. The resulting archive contains all files and directories in /usr/glenn except for file ./foo and all files and directories in /usr/gaston except for files ./foor, ./bar, and ./logs/logfile. To create a tar archive as a disk file, enter: tar cvf /tmp/mybackup.tar -e $HOME/zeugma $HOME
The preceding command line uses the f option to create a tar archive named mybackup.tar in the /tmp directory. The archive contains the user's home directory and its contents, including all subdirectories and files except the zeugma subdirectory and its contents, which are excluded by the -e (exception) option.
 

ENVIRONMENT VARIABLES

The following environment variables affect the execution of tar: Provides a default value for the internationalization variables that are unset or null. If LANG is unset or null, the corresponding value from the default locale is used. If any of the internationalization variables contain an invalid setting, the utility behaves as if none of the variables had been defined. If set to a non-empty string value, overrides the values of all the other internationalization variables. Determines the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to multibyte characters in arguments). Determines the locale for the format and contents of diagnostic messages written to standard error. Determines the format of date and time strings output when listing the contents of an archive. Determines the location of message catalogs for the processing of LC_MESSAGES. Determines the time zone used with date and time strings.
 

FILES

Device name used with the n option. Temporary file used with the u function.
 

SEE ALSO

Commands:  cpio(1), pax(1)

Functions:  chdir(2), umask(2)

Files:  tar(4)

Standards:  standards(5)


 

Index

NAME
SYNOPSIS
STANDARDS
FUNCTION KEYS
OPTIONS
DESCRIPTION
NOTES
EXIT STATUS
EXAMPLES
ENVIRONMENT VARIABLES
FILES
SEE ALSO

This document was created by man2html, using the manual pages.
Time: 02:43:05 GMT, October 02, 2010