1TAR(5) BSD File Formats Manual TAR(5)
2
4 tar — format of tape archive files
5
7 The tar archive format collects any number of files, directories, and
8 other file system objects (symbolic links, device nodes, etc.) into a
9 single stream of bytes. The format was originally designed to be used
10 with tape drives that operate with fixed-size blocks, but is widely used
11 as a general packaging mechanism.
12 General Format
14 A tar archive consists of a series of 512-byte records. Each file system
15 object requires a header record which stores basic metadata (pathname,
16 owner, permissions, etc.) and zero or more records containing any file
17 data. The end of the archive is indicated by two records consisting
18 entirely of zero bytes.
19 For compatibility with tape drives that use fixed block sizes, programs
21 that read or write tar files always read or write a fixed number of
22 records with each I/O operation. These “blocks” are always a multiple of
23 the record size. The maximum block size supported by early implementa‐
24 tions was 10240 bytes or 20 records. This is still the default for most
25 implementations although block sizes of 1MiB (2048 records) or larger are
26 commonly used with modern high-speed tape drives. (Note: the terms
27 “block” and “record” here are not entirely standard; this document fol‐
28 lows the convention established by John Gilmore in documenting pdtar.)
29 Old-Style Archive Format
31 The original tar archive format has been extended many times to include
32 additional information that various implementors found necessary. This
33 section describes the variant implemented by the tar command included in
34 Version 7 AT&T UNIX, which seems to be the earliest widely-used version
35 of the tar program.
36 The header record for an old-style tar archive consists of the following:
38 struct header_old_tar {
40 char name[100];
41 char mode[8];
42 char uid[8];
43 char gid[8];
44 char size[12];
45 char mtime[12];
46 char checksum[8];
47 char linkflag[1];
48 char linkname[100];
49 char pad[255];
50 };
51 All unused bytes in the header record are filled with nulls.
52 name Pathname, stored as a null-terminated string. Early tar imple‐
54 mentations only stored regular files (including hardlinks to
55 those files). One common early convention used a trailing "/"
56 character to indicate a directory name, allowing directory per‐
57 missions and owner information to be archived and restored.
58 mode File mode, stored as an octal number in ASCII.
60 uid, gid
62 User id and group id of owner, as octal numbers in ASCII.
63 size Size of file, as octal number in ASCII. For regular files only,
65 this indicates the amount of data that follows the header. In
66 particular, this field was ignored by early tar implementations
67 when extracting hardlinks. Modern writers should always store a
68 zero length for hardlink entries.
69 mtime Modification time of file, as an octal number in ASCII. This
71 indicates the number of seconds since the start of the epoch,
72 00:00:00 UTC January 1, 1970. Note that negative values should
73 be avoided here, as they are handled inconsistently.
74 checksum
76 Header checksum, stored as an octal number in ASCII. To compute
77 the checksum, set the checksum field to all spaces, then sum all
78 bytes in the header using unsigned arithmetic. This field should
79 be stored as six octal digits followed by a null and a space
80 character. Note that many early implementations of tar used
81 signed arithmetic for the checksum field, which can cause inter‐
82 operability problems when transferring archives between systems.
83 Modern robust readers compute the checksum both ways and accept
84 the header if either computation matches.
85 linkflag, linkname
87 In order to preserve hardlinks and conserve tape, a file with
88 multiple links is only written to the archive the first time it
89 is encountered. The next time it is encountered, the linkflag is
90 set to an ASCII ‘1’ and the linkname field holds the first name
91 under which this file appears. (Note that regular files have a
92 null value in the linkflag field.)
93 Early tar implementations varied in how they terminated these fields.
95 The tar command in Version 7 AT&T UNIX used the following conventions
96 (this is also documented in early BSD manpages): the pathname must be
97 null-terminated; the mode, uid, and gid fields must end in a space and a
98 null byte; the size and mtime fields must end in a space; the checksum is
99 terminated by a null and a space. Early implementations filled the
100 numeric fields with leading spaces. This seems to have been common prac‐
101 tice until the IEEE Std 1003.1-1988 (“POSIX.1”) standard was released.
102 For best portability, modern implementations should fill the numeric
103 fields with leading zeros.
104 Pre-POSIX Archives
106 An early draft of IEEE Std 1003.1-1988 (“POSIX.1”) served as the basis
107 for John Gilmore's pdtar program and many system implementations from the
108 late 1980s and early 1990s. These archives generally follow the POSIX
109 ustar format described below with the following variations:
110 · The magic value consists of the five characters “ustar” followed
111 by a space. The version field contains a space character fol‐
112 lowed by a null.
113 · The numeric fields are generally filled with leading spaces (not
114 leading zeros as recommended in the final standard).
115 · The prefix field is often not used, limiting pathnames to the 100
116 characters of old-style archives.
117 POSIX ustar Archives
119 IEEE Std 1003.1-1988 (“POSIX.1”) defined a standard tar file format to be
120 read and written by compliant implementations of tar(1). This format is
121 often called the “ustar” format, after the magic value used in the
122 header. (The name is an acronym for “Unix Standard TAR”.) It extends
123 the historic format with new fields:
124 struct header_posix_ustar {
126 char name[100];
127 char mode[8];
128 char uid[8];
129 char gid[8];
130 char size[12];
131 char mtime[12];
132 char checksum[8];
133 char typeflag[1];
134 char linkname[100];
135 char magic[6];
136 char version[2];
137 char uname[32];
138 char gname[32];
139 char devmajor[8];
140 char devminor[8];
141 char prefix[155];
142 char pad[12];
143 };
144 typeflag
146 Type of entry. POSIX extended the earlier linkflag field with
147 several new type values:
148 “0” Regular file. NUL should be treated as a synonym, for
149 compatibility purposes.
150 “1” Hard link.
151 “2” Symbolic link.
152 “3” Character device node.
153 “4” Block device node.
154 “5” Directory.
155 “6” FIFO node.
156 “7” Reserved.
157 Other A POSIX-compliant implementation must treat any unrecog‐
158 nized typeflag value as a regular file. In particular,
159 writers should ensure that all entries have a valid file‐
160 name so that they can be restored by readers that do not
161 support the corresponding extension. Uppercase letters
162 "A" through "Z" are reserved for custom extensions. Note
163 that sockets and whiteout entries are not archivable.
164 It is worth noting that the size field, in particular, has dif‐
165 ferent meanings depending on the type. For regular files, of
166 course, it indicates the amount of data following the header.
167 For directories, it may be used to indicate the total size of all
168 files in the directory, for use by operating systems that pre-
169 allocate directory space. For all other types, it should be set
170 to zero by writers and ignored by readers.
171 magic Contains the magic value “ustar” followed by a NUL byte to indi‐
173 cate that this is a POSIX standard archive. Full compliance
174 requires the uname and gname fields be properly set.
175 version
177 Version. This should be “00” (two copies of the ASCII digit
178 zero) for POSIX standard archives.
179 uname, gname
181 User and group names, as null-terminated ASCII strings. These
182 should be used in preference to the uid/gid values when they are
183 set and the corresponding names exist on the system.
184 devmajor, devminor
186 Major and minor numbers for character device or block device
187 entry.
188 name, prefix
190 If the pathname is too long to fit in the 100 bytes provided by
191 the standard format, it can be split at any / character with the
192 first portion going into the prefix field. If the prefix field
193 is not empty, the reader will prepend the prefix value and a /
194 character to the regular name field to obtain the full pathname.
195 The standard does not require a trailing / character on directory
196 names, though most implementations still include this for compat‐
197 ibility reasons.
198 Note that all unused bytes must be set to NUL.
200 Field termination is specified slightly differently by POSIX than by pre‐
202 vious implementations. The magic, uname, and gname fields must have a
203 trailing NUL. The pathname, linkname, and prefix fields must have a
204 trailing NUL unless they fill the entire field. (In particular, it is
205 possible to store a 256-character pathname if it happens to have a / as
206 the 156th character.) POSIX requires numeric fields to be zero-padded in
207 the front, and requires them to be terminated with either space or NUL
208 characters.
209 Currently, most tar implementations comply with the ustar format, occa‐
211 sionally extending it by adding new fields to the blank area at the end
212 of the header record.
213 Numeric Extensions
215 There have been several attempts to extend the range of sizes or times
216 supported by modifying how numbers are stored in the header.
217 One obvious extension to increase the size of files is to eliminate the
219 terminating characters from the various numeric fields. For example, the
220 standard only allows the size field to contain 11 octal digits, reserving
221 the twelfth byte for a trailing NUL character. Allowing 12 octal digits
222 allows file sizes up to 64 GB.
223 Another extension, utilized by GNU tar, star, and other newer tar imple‐
225 mentations, permits binary numbers in the standard numeric fields. This
226 is flagged by setting the high bit of the first byte. The remainder of
227 the field is treated as a signed twos-complement value. This permits
228 95-bit values for the length and time fields and 63-bit values for the
229 uid, gid, and device numbers. In particular, this provides a consistent
230 way to handle negative time values. GNU tar supports this extension for
231 the length, mtime, ctime, and atime fields. Joerg Schilling's star pro‐
232 gram and the libarchive library support this extension for all numeric
233 fields. Note that this extension is largely obsoleted by the extended
234 attribute record provided by the pax interchange format.
235 Another early GNU extension allowed base-64 values rather than octal.
237 This extension was short-lived and is no longer supported by any imple‐
238 mentation.
239 Pax Interchange Format
241 There are many attributes that cannot be portably stored in a POSIX ustar
242 archive. IEEE Std 1003.1-2001 (“POSIX.1”) defined a “pax interchange
243 format” that uses two new types of entries to hold text-formatted meta‐
244 data that applies to following entries. Note that a pax interchange for‐
245 mat archive is a ustar archive in every respect. The new data is stored
246 in ustar-compatible archive entries that use the “x” or “g” typeflag. In
247 particular, older implementations that do not fully support these exten‐
248 sions will extract the metadata into regular files, where the metadata
249 can be examined as necessary.
250 An entry in a pax interchange format archive consists of one or two stan‐
252 dard ustar entries, each with its own header and data. The first
253 optional entry stores the extended attributes for the following entry.
254 This optional first entry has an "x" typeflag and a size field that indi‐
255 cates the total size of the extended attributes. The extended attributes
256 themselves are stored as a series of text-format lines encoded in the
257 portable UTF-8 encoding. Each line consists of a decimal number, a
258 space, a key string, an equals sign, a value string, and a new line. The
259 decimal number indicates the length of the entire line, including the
260 initial length field and the trailing newline. An example of such a
261 field is:
262 25 ctime=1084839148.1212\n
263 Keys in all lowercase are standard keys. Vendors can add their own keys
264 by prefixing them with an all uppercase vendor name and a period. Note
265 that, unlike the historic header, numeric values are stored using deci‐
266 mal, not octal. A description of some common keys follows:
267 atime, ctime, mtime
269 File access, inode change, and modification times. These fields
270 can be negative or include a decimal point and a fractional
271 value.
272 hdrcharset
274 The character set used by the pax extension values. By default,
275 all textual values in the pax extended attributes are assumed to
276 be in UTF-8, including pathnames, user names, and group names.
277 In some cases, it is not possible to translate local conventions
278 into UTF-8. If this key is present and the value is the six-
279 character ASCII string “BINARY”, then all textual values are
280 assumed to be in a platform-dependent multi-byte encoding. Note
281 that there are only two valid values for this key: “BINARY” or
282 “ISO-IR 10646 2000 UTF-8”. No other values are permitted by the
283 standard, and the latter value should generally not be used as it
284 is the default when this key is not specified. In particular,
285 this flag should not be used as a general mechanism to allow
286 filenames to be stored in arbitrary encodings.
287 uname, uid, gname, gid
289 User name, group name, and numeric UID and GID values. The user
290 name and group name stored here are encoded in UTF8 and can thus
291 include non-ASCII characters. The UID and GID fields can be of
292 arbitrary length.
293 linkpath
295 The full path of the linked-to file. Note that this is encoded
296 in UTF8 and can thus include non-ASCII characters.
297 path The full pathname of the entry. Note that this is encoded in
299 UTF8 and can thus include non-ASCII characters.
300 realtime.*, security.*
302 These keys are reserved and may be used for future standardiza‐
303 tion.
304 size The size of the file. Note that there is no length limit on this
306 field, allowing conforming archives to store files much larger
307 than the historic 8GB limit.
308 SCHILY.*
310 Vendor-specific attributes used by Joerg Schilling's star imple‐
311 mentation.
312 SCHILY.acl.access, SCHILY.acl.default
314 Stores the access and default ACLs as textual strings in a format
315 that is an extension of the format specified by POSIX.1e draft
316 17. In particular, each user or group access specification can
317 include a fourth colon-separated field with the numeric UID or
318 GID. This allows ACLs to be restored on systems that may not
319 have complete user or group information available (such as when
320 NIS/YP or LDAP services are temporarily unavailable).
321 SCHILY.devminor, SCHILY.devmajor
323 The full minor and major numbers for device nodes.
324 SCHILY.fflags
326 The file flags.
327 SCHILY.realsize
329 The full size of the file on disk. XXX explain? XXX
330 SCHILY.dev, SCHILY.ino, SCHILY.nlinks
332 The device number, inode number, and link count for the entry.
333 In particular, note that a pax interchange format archive using
334 Joerg Schilling's SCHILY.* extensions can store all of the data
335 from struct stat.
336 LIBARCHIVE.*
338 Vendor-specific attributes used by the libarchive library and
339 programs that use it.
340 LIBARCHIVE.creationtime
342 The time when the file was created. (This should not be confused
343 with the POSIX “ctime” attribute, which refers to the time when
344 the file metadata was last changed.)
345 LIBARCHIVE.xattr.namespace.key
347 Libarchive stores POSIX.1e-style extended attributes using keys
348 of this form. The key value is URL-encoded: All non-ASCII char‐
349 acters and the two special characters “=” and “%” are encoded as
350 “%” followed by two uppercase hexadecimal digits. The value of
351 this key is the extended attribute value encoded in base 64. XXX
352 Detail the base-64 format here XXX
353 VENDOR.*
355 XXX document other vendor-specific extensions XXX
356 Any values stored in an extended attribute override the corresponding
358 values in the regular tar header. Note that compliant readers should
359 ignore the regular fields when they are overridden. This is important,
360 as existing archivers are known to store non-compliant values in the
361 standard header fields in this situation. There are no limits on length
362 for any of these fields. In particular, numeric fields can be arbitrar‐
363 ily large. All text fields are encoded in UTF8. Compliant writers
364 should store only portable 7-bit ASCII characters in the standard ustar
365 header and use extended attributes whenever a text value contains non-
366 ASCII characters.
367 In addition to the x entry described above, the pax interchange format
369 also supports a g entry. The g entry is identical in format, but speci‐
370 fies attributes that serve as defaults for all subsequent archive
371 entries. The g entry is not widely used.
372 Besides the new x and g entries, the pax interchange format has a few
374 other minor variations from the earlier ustar format. The most troubling
375 one is that hardlinks are permitted to have data following them. This
376 allows readers to restore any hardlink to a file without having to rewind
377 the archive to find an earlier entry. However, it creates complications
378 for robust readers, as it is no longer clear whether or not they should
379 ignore the size field for hardlink entries.
380 GNU Tar Archives
382 The GNU tar program started with a pre-POSIX format similar to that
383 described earlier and has extended it using several different mechanisms:
384 It added new fields to the empty space in the header (some of which was
385 later used by POSIX for conflicting purposes); it allowed the header to
386 be continued over multiple records; and it defined new entries that mod‐
387 ify following entries (similar in principle to the x entry described
388 above, but each GNU special entry is single-purpose, unlike the general-
389 purpose x entry). As a result, GNU tar archives are not POSIX compati‐
390 ble, although more lenient POSIX-compliant readers can successfully
391 extract most GNU tar archives.
392 struct header_gnu_tar {
394 char name[100];
395 char mode[8];
396 char uid[8];
397 char gid[8];
398 char size[12];
399 char mtime[12];
400 char checksum[8];
401 char typeflag[1];
402 char linkname[100];
403 char magic[6];
404 char version[2];
405 char uname[32];
406 char gname[32];
407 char devmajor[8];
408 char devminor[8];
409 char atime[12];
410 char ctime[12];
411 char offset[12];
412 char longnames[4];
413 char unused[1];
414 struct {
415 char offset[12];
416 char numbytes[12];
417 } sparse[4];
418 char isextended[1];
419 char realsize[12];
420 char pad[17];
421 };
422 typeflag
424 GNU tar uses the following special entry types, in addition to
425 those defined by POSIX:
426 7 GNU tar treats type "7" records identically to type "0"
428 records, except on one obscure RTOS where they are used
429 to indicate the pre-allocation of a contiguous file on
430 disk.
431 D This indicates a directory entry. Unlike the POSIX-stan‐
433 dard "5" typeflag, the header is followed by data records
434 listing the names of files in this directory. Each name
435 is preceded by an ASCII "Y" if the file is stored in this
436 archive or "N" if the file is not stored in this archive.
437 Each name is terminated with a null, and an extra null
438 marks the end of the name list. The purpose of this
439 entry is to support incremental backups; a program
440 restoring from such an archive may wish to delete files
441 on disk that did not exist in the directory when the ar‐
442 chive was made.
443 Note that the "D" typeflag specifically violates POSIX,
445 which requires that unrecognized typeflags be restored as
446 normal files. In this case, restoring the "D" entry as a
447 file could interfere with subsequent creation of the
448 like-named directory.
449 K The data for this entry is a long linkname for the fol‐
451 lowing regular entry.
452 L The data for this entry is a long pathname for the fol‐
454 lowing regular entry.
455 M This is a continuation of the last file on the previous
457 volume. GNU multi-volume archives guarantee that each
458 volume begins with a valid entry header. To ensure this,
459 a file may be split, with part stored at the end of one
460 volume, and part stored at the beginning of the next vol‐
461 ume. The "M" typeflag indicates that this entry contin‐
462 ues an existing file. Such entries can only occur as the
463 first or second entry in an archive (the latter only if
464 the first entry is a volume label). The size field spec‐
465 ifies the size of this entry. The offset field at bytes
466 369-380 specifies the offset where this file fragment
467 begins. The realsize field specifies the total size of
468 the file (which must equal size plus offset). When
469 extracting, GNU tar checks that the header file name is
470 the one it is expecting, that the header offset is in the
471 correct sequence, and that the sum of offset and size is
472 equal to realsize.
473 N Type "N" records are no longer generated by GNU tar.
475 They contained a list of files to be renamed or symlinked
476 after extraction; this was originally used to support
477 long names. The contents of this record are a text
478 description of the operations to be done, in the form
479 “Rename %s to %s\n” or “Symlink %s to %s\n”; in either
480 case, both filenames are escaped using K&R C syntax. Due
481 to security concerns, "N" records are now generally
482 ignored when reading archives.
483 S This is a “sparse” regular file. Sparse files are stored
485 as a series of fragments. The header contains a list of
486 fragment offset/length pairs. If more than four such
487 entries are required, the header is extended as necessary
488 with “extra” header extensions (an older format that is
489 no longer used), or “sparse” extensions.
490 V The name field should be interpreted as a tape/volume
492 header name. This entry should generally be ignored on
493 extraction.
494 magic The magic field holds the five characters “ustar” followed by a
496 space. Note that POSIX ustar archives have a trailing null.
497 version
499 The version field holds a space character followed by a null.
500 Note that POSIX ustar archives use two copies of the ASCII digit
501 “0”.
502 atime, ctime
504 The time the file was last accessed and the time of last change
505 of file information, stored in octal as with mtime.
506 longnames
508 This field is apparently no longer used.
509 Sparse offset / numbytes
511 Each such structure specifies a single fragment of a sparse file.
512 The two fields store values as octal numbers. The fragments are
513 each padded to a multiple of 512 bytes in the archive. On
514 extraction, the list of fragments is collected from the header
515 (including any extension headers), and the data is then read and
516 written to the file at appropriate offsets.
517 isextended
519 If this is set to non-zero, the header will be followed by addi‐
520 tional “sparse header” records. Each such record contains infor‐
521 mation about as many as 21 additional sparse blocks as shown
522 here:
523 struct gnu_sparse_header {
525 struct {
526 char offset[12];
527 char numbytes[12];
528 } sparse[21];
529 char isextended[1];
530 char padding[7];
531 };
532 realsize
534 A binary representation of the file's complete size, with a much
535 larger range than the POSIX file size. In particular, with M
536 type files, the current entry is only a portion of the file. In
537 that case, the POSIX size field will indicate the size of this
538 entry; the realsize field will indicate the total size of the
539 file.
540 GNU tar pax archives
542 GNU tar 1.14 (XXX check this XXX) and later will write pax interchange
543 format archives when you specify the --posix flag. This format follows
544 the pax interchange format closely, using some SCHILY tags and introduc‐
545 ing new keywords to store sparse file information. There have been three
546 iterations of the sparse file support, referred to as “0.0”, “0.1”, and
547 “1.0”.
548 GNU.sparse.numblocks, GNU.sparse.offset, GNU.sparse.numbytes,
550 GNU.sparse.size
551 The “0.0” format used an initial GNU.sparse.numblocks attribute
552 to indicate the number of blocks in the file, a pair of
553 GNU.sparse.offset and GNU.sparse.numbytes to indicate the offset
554 and size of each block, and a single GNU.sparse.size to indicate
555 the full size of the file. This is not the same as the size in
556 the tar header because the latter value does not include the size
557 of any holes. This format required that the order of attributes
558 be preserved and relied on readers accepting multiple appearances
559 of the same attribute names, which is not officially permitted by
560 the standards.
561 GNU.sparse.map
563 The “0.1” format used a single attribute that stored a comma-sep‐
564 arated list of decimal numbers. Each pair of numbers indicated
565 the offset and size, respectively, of a block of data. This does
566 not work well if the archive is extracted by an archiver that
567 does not recognize this extension, since many pax implementations
568 simply discard unrecognized attributes.
569 GNU.sparse.major, GNU.sparse.minor, GNU.sparse.name, GNU.sparse.realsize
571 The “1.0” format stores the sparse block map in one or more
572 512-byte blocks prepended to the file data in the entry body.
573 The pax attributes indicate the existence of this map (via the
574 GNU.sparse.major and GNU.sparse.minor fields) and the full size
575 of the file. The GNU.sparse.name holds the true name of the
576 file. To avoid confusion, the name stored in the regular tar
577 header is a modified name so that extraction errors will be
578 apparent to users.
579 Solaris Tar
581 XXX More Details Needed XXX
582 Solaris tar (beginning with SunOS XXX 5.7 ?? XXX) supports an “extended”
584 format that is fundamentally similar to pax interchange format, with the
585 following differences:
586 · Extended attributes are stored in an entry whose type is X, not
587 x, as used by pax interchange format. The detailed format of
588 this entry appears to be the same as detailed above for the x
589 entry.
590 · An additional A header is used to store an ACL for the following
591 regular entry. The body of this entry contains a seven-digit
592 octal number followed by a zero byte, followed by the textual ACL
593 description. The octal value is the number of ACL entries plus a
594 constant that indicates the ACL type: 01000000 for POSIX.1e ACLs
595 and 03000000 for NFSv4 ACLs.
596 AIX Tar
598 XXX More details needed XXX
599 AIX Tar uses a ustar-formatted header with the type A for storing coded
601 ACL information. Unlike the Solaris format, AIX tar writes this header
602 after the regular file body to which it applies. The pathname in this
603 header is either NFS4 or AIXC to indicate the type of ACL stored. The
604 actual ACL is stored in platform-specific binary format.
605 Mac OS X Tar
607 The tar distributed with Apple's Mac OS X stores most regular files as
608 two separate files in the tar archive. The two files have the same name
609 except that the first one has “._” prepended to the last path element.
610 This special file stores an AppleDouble-encoded binary blob with addi‐
611 tional metadata about the second file, including ACL, extended
612 attributes, and resources. To recreate the original file on disk, each
613 separate file can be extracted and the Mac OS X copyfile() function can
614 be used to unpack the separate metadata file and apply it to th regular
615 file. Conversely, the same function provides a “pack” option to encode
616 the extended metadata from a file into a separate file whose contents can
617 then be put into a tar archive.
618 Note that the Apple extended attributes interact badly with long file‐
620 names. Since each file is stored with the full name, a separate set of
621 extensions needs to be included in the archive for each one, doubling the
622 overhead required for files with long names.
623 Summary of tar type codes
625 The following list is a condensed summary of the type codes used in tar
626 header records generated by different tar implementations. More details
627 about specific implementations can be found above:
628 NUL Early tar programs stored a zero byte for regular files.
629 0 POSIX standard type code for a regular file.
630 1 POSIX standard type code for a hard link description.
631 2 POSIX standard type code for a symbolic link description.
632 3 POSIX standard type code for a character device node.
633 4 POSIX standard type code for a block device node.
634 5 POSIX standard type code for a directory.
635 6 POSIX standard type code for a FIFO.
636 7 POSIX reserved.
637 7 GNU tar used for pre-allocated files on some systems.
638 A Solaris tar ACL description stored prior to a regular file header.
639 A AIX tar ACL description stored after the file body.
640 D GNU tar directory dump.
641 K GNU tar long linkname for the following header.
642 L GNU tar long pathname for the following header.
643 M GNU tar multivolume marker, indicating the file is a continuation of
644 a file from the previous volume.
645 N GNU tar long filename support. Deprecated.
646 S GNU tar sparse regular file.
647 V GNU tar tape/volume header name.
648 X Solaris tar general-purpose extension header.
649 g POSIX pax interchange format global extensions.
650 x POSIX pax interchange format per-file extensions.
651
653 ar(1), pax(1), tar(1)
654
656 The tar utility is no longer a part of POSIX or the Single Unix Standard.
657 It last appeared in Version 2 of the Single UNIX Specification (“SUSv2”).
658 It has been supplanted in subsequent standards by pax(1). The ustar for‐
659 mat is currently part of the specification for the pax(1) utility. The
660 pax interchange file format is new with IEEE Std 1003.1-2001 (“POSIX.1”).
661
663 A tar command appeared in Seventh Edition Unix, which was released in
664 January, 1979. It replaced the tp program from Fourth Edition Unix which
665 in turn replaced the tap program from First Edition Unix. John Gilmore's
666 pdtar public-domain implementation (circa 1987) was highly influential
667 and formed the basis of GNU tar (circa 1988). Joerg Shilling's star
668 archiver is another open-source (GPL) archiver (originally developed
669 circa 1985) which features complete support for pax interchange format.
670 This documentation was written as part of the libarchive and bsdtar
672 project by Tim Kientzle <kientzle@FreeBSD.org>.
673BSD December 23, 2011 BSD