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GNU Info File | 1996-10-12 | 36.3 KB | 767 lines

This is Info file tar.info, produced by Makeinfo-1.64 from the input file /ade-src/fsf/tar/doc/tar.texinfo. START-INFO-DIR-ENTRY * tar: (tar). Making tape (or disk) archives. END-INFO-DIR-ENTRY This file documents GNU `tar', a utility used to store, backup, and transport files. Copyright (C) 1992, 1994, 1995 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Foundation. File: tar.info, Node: Standard, Next: Extensions, Prev: Archive Format, Up: Archive Format The Standard Format =================== *(This message will disappear, once this node revised.)* A `tar' archive file contains a series of records. Each record contains `RECORDSIZE' bytes. Although this format may be thought of as being on magnetic tape, other media are often used. Each file archived is represented by a header record which describes the file, followed by zero or more records which give the contents of the file. At the end of the archive file there may be a record filled with binary zeros as an end-of-file marker. A reasonable system should write a record of zeros at the end, but must not assume that such a record exists when reading an archive. The records may be "blocked" for physical I/O operations. Each block of N records (where N is set by the `--block-size=512-SIZE' (`-b 512-SIZE') option to `tar') is written with a single `write ()' operation. On magnetic tapes, the result of such a write is a single tape record. When writing an archive, the last block of records should be written at the full size, with records after the zero record containing all zeroes. When reading an archive, a reasonable system should properly handle an archive whose last block is shorter than the rest, or which contains garbage records after a zero record. The header record is defined in C as follows. In the GNU `tar' distribution, this is part of file `src/tar.h': /* Standard Archive Format - Standard TAR - USTAR. */ /* Header block on tape. We use traditional DP naming conventions here. A "block" is a big chunk of stuff that we do I/O on. A "record" is a piece of info that we care about. Typically many "record"s fit into a "block". */ #define RECORDSIZE 512 #define NAMSIZ 100 #define TUNMLEN 32 #define TGNMLEN 32 #define SPARSE_EXT_HDR 21 #define SPARSE_IN_HDR 4 struct sparse { char offset[12]; char numbytes[12]; }; union record { char charptr[RECORDSIZE]; struct header { char arch_name[NAMSIZ]; char mode[8]; char uid[8]; char gid[8]; char size[12]; char mtime[12]; char chksum[8]; char linkflag; char arch_linkname[NAMSIZ]; char magic[8]; char uname[TUNMLEN]; char gname[TGNMLEN]; char devmajor[8]; char devminor[8]; /* The following fields were added for GNU and are not standard. */ char atime[12]; char ctime[12]; char offset[12]; char longnames[4]; /* Some compilers would insert the pad themselves, so pad was once autoconfigured. It is simpler to always insert it! */ char pad; struct sparse sp[SPARSE_IN_HDR]; char isextended; char realsize[12]; /* true size of the sparse file */ #if 0 char ending_blanks[12]; /* number of nulls at the end of the file, if any */ #endif } header; struct extended_header { struct sparse sp[21]; char isextended; } ext_hdr; }; /* The checksum field is filled with this while the checksum is computed. */ #define CHKBLANKS " " /* 8 blanks, no null */ /* The magic field is filled with this value if uname and gname are valid, marking the archive as being in standard POSIX format (though GNU tar itself is not POSIX conforming). */ #define TMAGIC "ustar " /* 7 chars and a null */ /* The magic field is filled with this if this is a GNU format dump entry. But I suspect this is not true anymore. */ #define GNUMAGIC "GNUtar " /* 7 chars and a null */ /* The linkflag defines the type of file. */ #define LF_OLDNORMAL '\0' /* normal disk file, Unix compat */ #define LF_NORMAL '0' /* normal disk file */ #define LF_LINK '1' /* link to previously dumped file */ #define LF_SYMLINK '2' /* symbolic link */ #define LF_CHR '3' /* character special file */ #define LF_BLK '4' /* block special file */ #define LF_DIR '5' /* directory */ #define LF_FIFO '6' /* FIFO special file */ #define LF_CONTIG '7' /* contiguous file */ /* Further link types may be defined later. */ /* Note that the standards committee allows only capital A through capital Z for user-defined expansion. This means that defining something as, say '8' is a *bad* idea. */ /* This is a dir entry that contains the names of files that were in the dir at the time the dump was made. */ #define LF_DUMPDIR 'D' /* Identifies the NEXT file on the tape as having a long linkname. */ #define LF_LONGLINK 'K' /* Identifies the NEXT file on the tape as having a long name. */ #define LF_LONGNAME 'L' /* This is the continuation of a file that began on another volume. */ #define LF_MULTIVOL 'M' /* For storing filenames that didn't fit in 100 characters. */ #define LF_NAMES 'N' /* This is for sparse files. */ #define LF_SPARSE 'S' /* This file is a tape/volume header. Ignore it on extraction. */ #define LF_VOLHDR 'V' #if 0 /* The following two blocks of #define's are unused in GNU tar. */ /* Bits used in the mode field - values in octal */ #define TSUID 04000 /* set UID on execution */ #define TSGID 02000 /* set GID on execution */ #define TSVTX 01000 /* save text (sticky bit) */ /* File permissions */ #define TUREAD 00400 /* read by owner */ #define TUWRITE 00200 /* write by owner */ #define TUEXEC 00100 /* execute/search by owner */ #define TGREAD 00040 /* read by group */ #define TGWRITE 00020 /* write by group */ #define TGEXEC 00010 /* execute/search by group */ #define TOREAD 00004 /* read by other */ #define TOWRITE 00002 /* write by other */ #define TOEXEC 00001 /* execute/search by other */ #endif /* End of Standard Archive Format description. */ All characters in header records are represented by using 8-bit characters in the local variant of ASCII. Each field within the structure is contiguous; that is, there is no padding used within the structure. Each character on the archive medium is stored contiguously. Bytes representing the contents of files (after the header record of each file) are not translated in any way and are not constrained to represent characters in any character set. The `tar' format does not distinguish text files from binary files, and no translation of file contents is performed. The `name', `linkname', `magic', `uname', and `gname' are null-terminated character strings. All other fileds are zero-filled octal numbers in ASCII. Each numeric field of width W contains W minus 2 digits, a space, and a null, except `size', and `mtime', which do not contain the trailing null. The `name' field is the file name of the file, with directory names (if any) preceding the file name, separated by slashes. FIXME: how big a name before field overflows? The `mode' field provides nine bits specifying file permissions and three bits to specify the Set UID, Set GID, and Save Text ("sticky") modes. Values for these bits are defined above. When special permissions are required to create a file with a given mode, and the user restoring files from the archive does not hold such permissions, the mode bit(s) specifying those special permissions are ignored. Modes which are not supported by the operating system restoring files from the archive will be ignored. Unsupported modes should be faked up when creating or updating an archive; e.g. the group permission could be copied from the *other* permission. The `uid' and `gid' fields are the numeric user and group ID of the file owners, respectively. If the operating system does not support numeric user or group IDs, these fields should be ignored. The `size' field is the size of the file in bytes; linked files are archived with this field specified as zero. FIXME: xref Modifiers , in particular the `--incremental' (`-G') option. The `mtime' field is the modification time of the file at the time it was archived. It is the ASCII representation of the octal value of the last time the file was modified, represented as an integer number of seconds since January 1, 1970, 00:00 Coordinated Universal Time. The `chksum' field is the ASCII representation of the octal value of the simple sum of all bytes in the header record. Each 8-bit byte in the header is added to an unsigned integer, initialized to zero, the precision of which shall be no less than seventeen bits. When calculating the checksum, the `chksum' field is treated as if it were all blanks. The `typeflag' field specifies the type of file archived. If a particular implementation does not recognize or permit the specified type, the file will be extracted as if it were a regular file. As this action occurs, `tar' issues a warning to the standard error. The `atime' and `ctime' fields are used in making incremental backups; they store, respectively, the particular file's access time and last inode-change time. The `offset' is used by the `--multi-volume' (`-M') option, when making a multi-volume archive. The offset is number of bytes into the file that we need to restart at to continue the file on the next tape, i.e., where we store the location that a continued file is continued at. The following fields were added to deal with sparse files. A file is "sparse" if it takes in unallocated blocks which end up being represented as zeros, i.e., no useful data. A test to see if a file is sparse is to look at the number blocks allocated for it versus the number of characters in the file; if there are fewer blocks allocated for the file than would normally be allocated for a file of that size, then the file is sparse. This is the method `tar' uses to detect a sparse file, and once such a file is detected, it is treated differently from non-sparse files. Sparse files are often `dbm' files, or other database-type files which have data at some points and emptiness in the greater part of the file. Such files can appear to be very large when an `ls -l' is done on them, when in truth, there may be a very small amount of important data contained in the file. It is thus undesirable to have `tar' think that it must back up this entire file, as great quantities of room are wasted on empty blocks, which can lead to running out of room on a tape far earlier than is necessary. Thus, sparse files are dealt with so that these empty blocks are not written to the tape. Instead, what is written to the tape is a description, of sorts, of the sparse file: where the holes are, how big the holes are, and how much data is found at the end of the hole. This way, the file takes up potentially far less room on the tape, and when the file is extracted later on, it will look exactly the way it looked beforehand. The following is a description of the fields used to handle a sparse file: The `sp' is an array of `struct sparse'. Each `struct sparse' contains two 12-character strings which represent an offset into the file and a number of bytes to be written at that offset. The offset is absolute, and not relative to the offset in preceding array element. The header can hold four of these `struct sparse' at the moment; if more are needed, they are not stored in the header. The `isextended' flag is set when an `extended_header' is needed to deal with a file. Note that this means that this flag can only be set when dealing with a sparse file, and it is only set in the event that the description of the file will not fit in the alloted room for sparse structures in the header. In other words, an extended_header is needed. The `extended_header' structure is used for sparse files which need more sparse structures than can fit in the header. The header can fit 4 such structures; if more are needed, the flag `isextended' gets set and the next record is an `extended_header'. Each `extended_header' structure contains an array of 21 sparse structures, along with a similar `isextended' flag that the header had. There can be an indeterminate number of such `extended_header's to describe a sparse file. `LF_NORMAL' `LF_OLDNORMAL' These flags represent a regular file. In order to be compatible with older versions of `tar', a `typeflag' value of `LF_OLDNORMAL' should be silently recognized as a regular file. New archives should be created using `LF_NORMAL'. Also, for backward compatibility, `tar' treats a regular file whose name ends with a slash as a directory. `LF_LINK' This flag represents a file linked to another file, of any type, previously archived. Such files are identified in Unix by each file having the same device and inode number. The linked-to name is specified in the `linkname' field with a trailing null. `LF_SYMLINK' This represents a symbolic link to another file. The linked-to name is specified in the `linkname' field with a trailing null. `LF_CHR' `LF_BLK' These represent character special files and block special files respectively. In this case the `devmajor' and `devminor' fields will contain the major and minor device numbers respectively. Operating systems may map the device specifications to their own local specification, or may ignore the entry. `LF_DIR' This flag specifies a directory or sub-directory. The directory name in the `name' field should end with a slash. On systems where disk allocation is performed on a directory basis, the `size' field will contain the maximum number of bytes (which may be rounded to the nearest disk block allocation unit) which the directory may hold. A `size' field of zero indicates no such limiting. Systems which do not support limiting in this manner should ignore the `size' field. `LF_FIFO' This specifies a FIFO special file. Note that the archiving of a FIFO file archives the existence of this file and not its contents. `LF_CONTIG' This specifies a contiguous file, which is the same as a normal file except that, in operating systems which support it, all its space is allocated contiguously on the disk. Operating systems which do not allow contiguous allocation should silently treat this type as a normal file. `A' ... `Z' These are reserved for custom implementations. Some of these are used in the GNU modified format, as described below. Other values are reserved for specification in future revisions of the P1003 standard, and should not be used by any `tar' program. The `magic' field indicates that this archive was output in the P1003 archive format. If this field contains `TMAGIC', the `uname' and `gname' fields will contain the ASCII representation of the owner and group of the file respectively. If found, the user and group IDs are used rather than the values in the `uid' and `gid' fields. File: tar.info, Node: Extensions, Next: cpio, Prev: Standard, Up: Archive Format GNU Extensions to the Archive Format ==================================== *(This message will disappear, once this node revised.)* The GNU format uses additional file types to describe new types of files in an archive. These are listed below. `LF_DUMPDIR' `'D'' This represents a directory and a list of files created by the `--incremental' (`-G') option. The `size' field gives the total size of the associated list of files. Each file name is preceded by either a `Y' (the file should be in this archive) or an `N'. (The file is a directory, or is not stored in the archive.) Each file name is terminated by a null. There is an additional null after the last file name. `LF_MULTIVOL' `'M'' This represents a file continued from another volume of a multi-volume archive created with the `--multi-volume' (`-M') option. The original type of the file is not given here. The `size' field gives the maximum size of this piece of the file (assuming the volume does not end before the file is written out). The `offset' field gives the offset from the beginning of the file where this part of the file begins. Thus `size' plus `offset' should equal the original size of the file. `LF_SPARSE' `'S'' This flag indicates that we are dealing with a sparse file. Note that archiving a sparse file requires special operations to find holes in the file, which mark the positions of these holes, along with the number of bytes of data to be found after the hole. `LF_VOLHDR' `'V'' This file type is used to mark the volume header that was given with the `--label=ARCHIVE-LABEL' (`-V ARCHIVE-LABEL') option when the archive was created. The `name' field contains the `name' given after the `--label=ARCHIVE-LABEL' (`-V ARCHIVE-LABEL') option. The `size' field is zero. Only the first file in each volume of an archive should have this type. You may have trouble reading a GNU format archive on a non-GNU system if the options `--incremental' (`-G'), `--multi-volume' (`-M'), `--sparse' (`-S'), or `--label=ARCHIVE-LABEL' (`-V ARCHIVE-LABEL') were used when writing the archive. In general, if `tar' does not use the GNU-added fields of the header, other versions of `tar' should be able to read the archive. Otherwise, the `tar' program will give an error, the most likely one being a checksum error. File: tar.info, Node: cpio, Prev: Extensions, Up: Archive Format Comparison of `tar' and `cpio' ============================== *(This message will disappear, once this node revised.)* Here is a summary of differences between `tar' and `cpio'. The accuracy of the following information has not been verified. The following people contributed to this section, mainly through a survey conducted in 1991. The remainder of this section does not otherwise try to relate topics to people. Bent Bertelsen dmdata@login.dkuug.dk David Hoopes talgras!david Guy Harris guy@auspex.com Kai Petzke wpp@marie.physik.tu-berlin.de Kristen Nielsen dmdata@login.dkuug.dk Leslie Mikesell les@chinet.chi.il.us FIXME: Reorganize the following material `tar' handles symbolic links in the form in which it comes in BSD; `cpio' doesn't handle symbolic links in the form in which it comes in System V prior to SVR4, and some vendors may have added symlinks to their system without enhancing `cpio' to know about them. Others may have enhanced it in a way other than the way I did it at Sun, and which was adopted by AT&T (and which is, I think, also present in the `cpio' that Berkeley picked up from AT&T and put into a later BSD release--I think I gave them my changes). (SVR4 does some funny stuff with `tar'; basically, its `cpio' can handle `tar' format input, and write it on output, and it probably handles symbolic links. They may not have bothered doing anything to enhance `tar' as a result.) `cpio' handles special files; traditional `tar' doesn't. `tar' comes with V7, System III, System V, and BSD source; `cpio' comes only with System III, System V, and later BSD (4.3-tahoe and later). `tar''s way of handling multiple hard links to a file can handle file systems that support 32-bit inumbers (e.g., the BSD file system); `cpio's way requires you to play some games (in its "binary" format, i-numbers are only 16 bits, and in its "portable ASCII" format, they're 18 bits--it would have to play games with the "file system ID" field of the header to make sure that the file system ID/i-number pairs of different files were always different), and I don't know which `cpio's, if any, play those games. Those that don't might get confused and think two files are the same file when they're not, and make hard links between them. `tar's way of handling multiple hard links to a file places only one copy of the link on the tape, but the name attached to that copy is the *only* one you can use to retrieve the file; `cpio's way puts one copy for every link, but you can retrieve it using any of the names. >What type of check sum (if any) is used, and how is this calculated. See the attached manual pages for `tar' and `cpio' format. `tar' uses a checksum which is the sum of all the bytes in the `tar' header for a file; `cpio' uses no checksum. >If anyone knows why `cpio' was made when `tar' was prasent >at the unix scene, It wasn't. `cpio' first showed up in PWB/UNIX 1.0; no generally-available version of UNIX had `tar' at the time. I don't know whether any version that was generally available *within AT&T* had `tar', or, if so, whether the people within AT&T who did `cpio' knew about it. On restore, if there is a corruption on a tape `tar' will stop at that point, while `cpio' will skip over it and try to restore the rest of the files. The main difference is just in the command syntax and header format. `tar' is a little more tape-oriented in that everything is blocked to start on a block boundary. >Is there any differences between the ability to recover crashed >archives between the two of them. (Is there any chance of recovering >crashed archives at all.) Theoretically it should be easier under `tar' since the blocking lets you find a header with some variation of `dd skip=NN'. However, modern `cpio''s and variations have an option to just search for the next file header after an error with a reasonable chance of re-syncing. However, lots of tape driver software won't allow you to continue past a media error which should be the only reason for getting out of sync unless a file changed sizes while you were writing the archive. >If anyone knows why `cpio' was made when `tar' was prasent >at the unix scene, please tell me about this too. Probably because it is more media efficient (by not blocking everything and using only the space needed for the headers where `tar' always uses 512 bytes per file header) and it knows how to archive special files. You might want to look at the freely available alternatives. The major ones are `afio', GNU `tar', and `pax', each of which have their own extensions with some backwards compatibility. Sparse files were `tar'red as sparse files (which you can easily test, because the resulting archive gets smaller, and GNU `cpio' can no longer read it). File: tar.info, Node: Index, Prev: Archive Format, Up: Top Index ***** * Menu: * abbreviations for months: Calendar date item. * absolute file names: Device. * Adding archives to an archive: Combining Archives. * Adding files to an archive: Adding to an Existing Archive. * Age, excluding files by: Characteristics. * ago in date strings: Relative item in date strings. * Alaska-Hawaii Time: Timezone item. * am in date strings: Time of day item. * archive: What tar Does. * Archive contents, list of: Listing Archive Members. * Archive creation: Creating a New Archive. * archive member: What tar Does. * Archive members, list of: Listing Archive Members. * Archive Name: Changing the Archive Name. * Atlantic Standard Time: Timezone item. * authors of getdate: Authors of getdate. * Azores Time: Timezone item. * Baghdad Time: Timezone item. * beginning of time, for Unix: Date input formats. * Bellovin, Steven M.: Authors of getdate. * Berets, Jim: Authors of getdate. * Berry, K.: Authors of getdate. * Block Size: Blocking Factor. * blocking factor: Blocking Factor. * Blocks, incomplete: Archive Reading Options. * bug reports: Bug reports. * Bytes per block: Blocking Factor. * calendar date item: Calendar date item. * case, ignored in dates: General date syntax. * Central Alaska Time: Timezone item. * Central European Time: Timezone item. * Central Standard Time: Timezone item. * China Coast Time: Timezone item. * comments, in dates: General date syntax. * Compressed archives: Compressed Archives. * Concatenating Archives: Combining Archives. * corrupted archives <1>: Type Options. * corrupted archives: Full Dumps. * DAT blocking: Blocking Factor. * date format, ISO 8601: Calendar date item. * date input formats: Date input formats. * day in date strings: Relative item in date strings. * day of week item: Day of week item. * daylight savings time: Timezone item. * Deleting files from an archive: Removing Archive Members. * Directing output: Changing the Archive Name. * directory arguments: Basic tar Operations. * Directory, changing in mid-stream: Changing Directory. * Disk space, running out of: Scarce Disk Space. * displacement of dates: Relative item in date strings. * Double-checking a write operation: Write Verification. * dumps, full: Full Dumps. * dumps, incremental: Inc Dumps. * East Australian Standard Time: Timezone item. * Eastern European Time: Timezone item. * Eastern Standard Time: Timezone item. * End-of-archive entries, ignoring: Archive Reading Options. * entry: What tar Does. * epoch, for Unix: Date input formats. * Error message, record number of: Checking Progress. * Exabyte blocking: Blocking Factor. * Excluding file by age: Characteristics. * Excluding files by file system: Characteristics. * Excluding files by name and pattern: Characteristics. * exit status: Synopsis. * extraction: What tar Does. * Extraction: Extracting Archive Members. * Feedback from tar: Checking Progress. * file name: What tar Does. * File Name arguments, alternatives: Reading Names from a File. * File names, excluding files by: Characteristics. * File names, using symbolic links: Symbolic Links. * File system boundaries, not crossing: Characteristics. * first in date strings: General date syntax. * Format Options: Format Variations. * Format Parameters: Format Variations. * Format, old style: Old V7 and POSIX. * fortnight in date strings: Relative item in date strings. * French Winter Time: Timezone item. * full dumps: Full Dumps. * general date syntax: General date syntax. * getdate: Date input formats. * Getting more information during the operation: Checking Progress. * Greenwich Mean Time: Timezone item. * Guam Standard Time: Timezone item. * Hawaii Standard Time: Timezone item. * hour in date strings: Relative item in date strings. * Ignoring end-of-archive entries: Archive Reading Options. * incompleteness of this manual: Authors. * incremental dumps: Inc Dumps. * Information during operation: Checking Progress. * Information on progress and status of operations: Checking Progress. * Interactive operation: Interactive Operation. * International Date Line East: Timezone item. * International Date Line West: Timezone item. * ISO 8601 date format: Calendar date item. * items in date strings: General date syntax. * Japan Standard Time: Timezone item. * Labeling an archive: Archive Label. * Labelling multi-volume archives: Matching Format Parameters. * Labels on the archive media: Archive Label. * Large lists of file names on small machines: Archive Reading Options. * last in date strings: General date syntax. * last DAY: Day of week item. * Lists of file names: Reading Names from a File. * MacKenzie, David: Authors of getdate. * member: What tar Does. * member name: What tar Does. * Meyering, Jim: Authors of getdate. * Middle European Time: Timezone item. * Middle European Winter Time: Timezone item. * Middle of the archive, starting in the: Scarce Disk Space. * midnight in date strings: Time of day item. * minute in date strings: Relative item in date strings. * minutes, timezone correction by: Time of day item. * Modes of extracted files: File Writing Options. * Modification time, excluding files by: Characteristics. * Modification times of extracted files: File Writing Options. * Modifying archives: Basic tar Operations. * month in date strings: Relative item in date strings. * month names in date strings: Calendar date item. * months, written-out: General date syntax. * Mountain Standard Time: Timezone item. * Multi-volume archives: Multi-Volume Archives. * Names of the files in an archive: Listing Archive Members. * Naming an archive: Changing the Archive Name. * New Zealand Standard Time: Timezone item. * next in date strings: General date syntax. * next DAY: Day of week item. * Nome Standard Time: Timezone item. * noon in date strings: Time of day item. * now in date strings: Relative item in date strings. * ntape device: Many. * Number of bytes per block: Blocking Factor. * Number of records per block: Blocking Factor. * numbers, written-out: General date syntax. * Old style archives: Old V7 and POSIX. * Old style format: Old V7 and POSIX. * option syntax, traditional: Old Options. * Options to specify archive format.: Format Variations. * Options when reading archives: Archive Reading Options. * ordinal numbers: General date syntax. * Overwriting old files, prevention: File Writing Options. * Pacific Standard Time: Timezone item. * Permissions of extracted files: File Writing Options. * Pinard, F.: Authors of getdate. * pm in date strings: Time of day item. * Progress information: Checking Progress. * Protecting old files: File Writing Options. * pure numbers in date strings: Pure numbers in date strings. * Reading incomplete blocks: Archive Reading Options. * Record number where error occured: Checking Progress. * Records per block: Blocking Factor. * relative items in date strings: Relative item in date strings. * remote tape drive: Device. * Removing files from an archive: Removing Archive Members. * reporting bugs: Bug reports. * Resurrecting files from an archive: Extracting Archive Members. * Retrieving files from an archive: Extracting Archive Members. * return status: Synopsis. * rmt: Device. * Running out of space: Archive Reading Options. * Running out of space during extraction: Scarce Disk Space. * Salz, Rich: Authors of getdate. * Small memory: Archive Reading Options. * Space on the disk, recovering from lack of: Scarce Disk Space. * Sparse Files: Sparse Files. * Specifying archive members: Changing the Archive Name. * Specifying files to act on: Changing the Archive Name. * Standard input and output: Changing the Archive Name. * Standard output, writing extracted files to: File Writing Options. * Status information: Checking Progress. * Storing archives in compressed format: Compressed Archives. * Swedish Winter Time: Timezone item. * Symbolic link as file name: Symbolic Links. * tape blocking: Blocking Factor. * tape marks: Many. * tape positioning: Many. * tar: What tar Does. * tar archive: What tar Does. * tar entry: What tar Does. * tar file: What tar Does. * tar to standard input and output: Changing the Archive Name. * this in date strings: Relative item in date strings. * time of day item: Time of day item. * timezone correction: Time of day item. * timezone item: Timezone item. * today in date strings: Relative item in date strings. * tomorrow in date strings: Relative item in date strings. * Ultrix 3.1 and write failure: Device. * Universal Coordinated Time: Timezone item. * unpacking: What tar Does. * Updating an archive: Adding to an Existing Archive. * USSR Zone: Timezone item. * uuencode: Modifiers Options. * Verbose operation: Checking Progress. * Verifying a write operation: Write Verification. * Verifying the currency of an archive: Comparing. * Version of the tar program: Checking Progress. * week in date strings: Relative item in date strings. * West African Time: Timezone item. * West Australian Standard Time: Timezone item. * Western European Time: Timezone item. * Where is the archive?: Changing the Archive Name. * Working directory, specifying: Changing Directory. * Writing extracted files to standard output: File Writing Options. * Writing new archives: Creating a New Archive. * year in date strings: Relative item in date strings. * yesterday in date strings: Relative item in date strings. * Yukon Standard Time: Timezone item.