TAR(5)			    BSD File Formats Manual			TAR(5)

1mNAME0m
     1mtar 22m— format of tape archive files

1mDESCRIPTION0m
     The 1mtar 22marchive format collects any number of files, directories, and
     other file system objects (symbolic links, device nodes, etc.) into a
     single stream of bytes.  The format was originally designed to be used
     with tape drives that operate with fixed-size blocks, but is widely used
     as a general packaging mechanism.

   1mGeneral Format0m
     A 1mtar 22marchive consists of a series of 512-byte records.  Each file system
     object requires a header record which stores basic metadata (pathname,
     owner, permissions, etc.) and zero or more records containing any file
     data.  The end of the archive is indicated by two records consisting
     entirely of zero bytes.

     For compatibility with tape drives that use fixed block sizes, programs
     that read or write tar files always read or write a fixed number of
     records with each I/O operation.  These “blocks” are always a multiple of
     the record size.  The maximum block size supported by early implementa‐
     tions was 10240 bytes or 20 records.  This is still the default for most
     implementations although block sizes of 1MiB (2048 records) or larger are
     commonly used with modern high-speed tape drives.	(Note: the terms
     “block” and “record” here are not entirely standard; this document fol‐
     lows the convention established by John Gilmore in documenting 1mpdtar22m.)

   1mOld-Style Archive Format0m
     The original tar archive format has been extended many times to include
     additional information that various implementors found necessary.	This
     section describes the variant implemented by the tar command included in
     Version 7 AT&T UNIX, which seems to be the earliest widely-used version
     of the tar program.

     The header record for an old-style 1mtar 22marchive consists of the following:

	   struct header_old_tar {
		   char name[100];
		   char mode[8];
		   char uid[8];
		   char gid[8];
		   char size[12];
		   char mtime[12];
		   char checksum[8];
		   char linkflag[1];
		   char linkname[100];
		   char pad[255];
	   };
     All unused bytes in the header record are filled with nulls.

     4mname24m	  Pathname, stored as a null-terminated string.  Early tar imple‐
	     mentations only stored regular files (including hardlinks to
	     those files).  One common early convention used a trailing "/"
	     character to indicate a directory name, allowing directory per‐
	     missions and owner information to be archived and restored.

     4mmode24m	  File mode, stored as an octal number in ASCII.

     4muid24m, 4mgid0m
	     User id and group id of owner, as octal numbers in ASCII.

     4msize24m	  Size of file, as octal number in ASCII.  For regular files only,
	     this indicates the amount of data that follows the header.  In
	     particular, this field was ignored by early tar implementations
	     when extracting hardlinks.  Modern writers should always store a
	     zero length for hardlink entries.

     4mmtime24m   Modification time of file, as an octal number in ASCII.  This
	     indicates the number of seconds since the start of the epoch,
	     00:00:00 UTC January 1, 1970.  Note that negative values should
	     be avoided here, as they are handled inconsistently.

     4mchecksum0m
	     Header checksum, stored as an octal number in ASCII.  To compute
	     the checksum, set the checksum field to all spaces, then sum all
	     bytes in the header using unsigned arithmetic.  This field should
	     be stored as six octal digits followed by a null and a space
	     character.  Note that many early implementations of tar used
	     signed arithmetic for the checksum field, which can cause inter‐
	     operability problems when transferring archives between systems.
	     Modern robust readers compute the checksum both ways and accept
	     the header if either computation matches.

     4mlinkflag24m, 4mlinkname0m
	     In order to preserve hardlinks and conserve tape, a file with
	     multiple links is only written to the archive the first time it
	     is encountered.  The next time it is encountered, the 4mlinkflag24m is
	     set to an ASCII ‘1’ and the 4mlinkname24m field holds the first name
	     under which this file appears.  (Note that regular files have a
	     null value in the 4mlinkflag24m field.)

     Early tar implementations varied in how they terminated these fields.
     The tar command in Version 7 AT&T UNIX used the following conventions
     (this is also documented in early BSD manpages): the pathname must be
     null-terminated; the mode, uid, and gid fields must end in a space and a
     null byte; the size and mtime fields must end in a space; the checksum is
     terminated by a null and a space.	Early implementations filled the
     numeric fields with leading spaces.  This seems to have been common prac‐
     tice until the IEEE Std 1003.1-1988 (“POSIX.1”) standard was released.
     For best portability, modern implementations should fill the numeric
     fields with leading zeros.

   1mPre-POSIX Archives0m
     An early draft of IEEE Std 1003.1-1988 (“POSIX.1”) served as the basis
     for John Gilmore's 1mpdtar 22mprogram and many system implementations from the
     late 1980s and early 1990s.  These archives generally follow the POSIX
     ustar format described below with the following variations:
     1m·       22mThe magic value consists of the five characters “ustar” followed
	     by a space.  The version field contains a space character fol‐
	     lowed by a null.
     1m·       22mThe numeric fields are generally filled with leading spaces (not
	     leading zeros as recommended in the final standard).
     1m·       22mThe prefix field is often not used, limiting pathnames to the 100
	     characters of old-style archives.

   1mPOSIX ustar Archives0m
     IEEE Std 1003.1-1988 (“POSIX.1”) defined a standard tar file format to be
     read and written by compliant implementations of tar(1).  This format is
     often called the “ustar” format, after the magic value used in the
     header.  (The name is an acronym for “Unix Standard TAR”.)  It extends
     the historic format with new fields:

	   struct header_posix_ustar {
		   char name[100];
		   char mode[8];
		   char uid[8];
		   char gid[8];
		   char size[12];
		   char mtime[12];
		   char checksum[8];
		   char typeflag[1];
		   char linkname[100];
		   char magic[6];
		   char version[2];
		   char uname[32];
		   char gname[32];
		   char devmajor[8];
		   char devminor[8];
		   char prefix[155];
		   char pad[12];
	   };

     4mtypeflag0m
	     Type of entry.  POSIX extended the earlier 4mlinkflag24m field with
	     several new type values:
	     “0”     Regular file.  NUL should be treated as a synonym, for
		     compatibility purposes.
	     “1”     Hard link.
	     “2”     Symbolic link.
	     “3”     Character device node.
	     “4”     Block device node.
	     “5”     Directory.
	     “6”     FIFO node.
	     “7”     Reserved.
	     Other   A POSIX-compliant implementation must treat any unrecog‐
		     nized typeflag value as a regular file.  In particular,
		     writers should ensure that all entries have a valid file‐
		     name so that they can be restored by readers that do not
		     support the corresponding extension.  Uppercase letters
		     "A" through "Z" are reserved for custom extensions.  Note
		     that sockets and whiteout entries are not archivable.
	     It is worth noting that the 4msize24m field, in particular, has dif‐
	     ferent meanings depending on the type.  For regular files, of
	     course, it indicates the amount of data following the header.
	     For directories, it may be used to indicate the total size of all
	     files in the directory, for use by operating systems that pre-
	     allocate directory space.	For all other types, it should be set
	     to zero by writers and ignored by readers.

     4mmagic24m   Contains the magic value “ustar” followed by a NUL byte to indi‐
	     cate that this is a POSIX standard archive.  Full compliance
	     requires the uname and gname fields be properly set.

     4mversion0m
	     Version.  This should be “00” (two copies of the ASCII digit
	     zero) for POSIX standard archives.

     4muname24m, 4mgname0m
	     User and group names, as null-terminated ASCII strings.  These
	     should be used in preference to the uid/gid values when they are
	     set and the corresponding names exist on the system.

     4mdevmajor24m, 4mdevminor0m
	     Major and minor numbers for character device or block device
	     entry.

     4mname24m, 4mprefix0m
	     If the pathname is too long to fit in the 100 bytes provided by
	     the standard format, it can be split at any 4m/24m character with the
	     first portion going into the prefix field.  If the prefix field
	     is not empty, the reader will prepend the prefix value and a 4m/0m
	     character to the regular name field to obtain the full pathname.
	     The standard does not require a trailing 4m/24m character on directory
	     names, though most implementations still include this for compat‐
	     ibility reasons.

     Note that all unused bytes must be set to NUL.

     Field termination is specified slightly differently by POSIX than by pre‐
     vious implementations.  The 4mmagic24m, 4muname24m, and 4mgname24m fields must have a
     trailing NUL.  The 4mpathname24m, 4mlinkname24m, and 4mprefix24m fields must have a
     trailing NUL unless they fill the entire field.  (In particular, it is
     possible to store a 256-character pathname if it happens to have a 4m/24m as
     the 156th character.)  POSIX requires numeric fields to be zero-padded in
     the front, and requires them to be terminated with either space or NUL
     characters.

     Currently, most tar implementations comply with the ustar format, occa‐
     sionally extending it by adding new fields to the blank area at the end
     of the header record.

   1mNumeric Extensions0m
     There have been several attempts to extend the range of sizes or times
     supported by modifying how numbers are stored in the header.

     One obvious extension to increase the size of files is to eliminate the
     terminating characters from the various numeric fields.  For example, the
     standard only allows the size field to contain 11 octal digits, reserving
     the twelfth byte for a trailing NUL character.  Allowing 12 octal digits
     allows file sizes up to 64 GB.

     Another extension, utilized by GNU tar, star, and other newer 1mtar 22mimple‐
     mentations, permits binary numbers in the standard numeric fields.  This
     is flagged by setting the high bit of the first byte.  The remainder of
     the field is treated as a signed twos-complement value.  This permits
     95-bit values for the length and time fields and 63-bit values for the
     uid, gid, and device numbers.  In particular, this provides a consistent
     way to handle negative time values.  GNU tar supports this extension for
     the length, mtime, ctime, and atime fields.  Joerg Schilling's star pro‐
     gram and the libarchive library support this extension for all numeric
     fields.  Note that this extension is largely obsoleted by the extended
     attribute record provided by the pax interchange format.

     Another early GNU extension allowed base-64 values rather than octal.
     This extension was short-lived and is no longer supported by any imple‐
     mentation.

   1mPax Interchange Format0m
     There are many attributes that cannot be portably stored in a POSIX ustar
     archive.  IEEE Std 1003.1-2001 (“POSIX.1”) defined a “pax interchange
     format” that uses two new types of entries to hold text-formatted meta‐
     data that applies to following entries.  Note that a pax interchange for‐
     mat archive is a ustar archive in every respect.  The new data is stored
     in ustar-compatible archive entries that use the “x” or “g” typeflag.  In
     particular, older implementations that do not fully support these exten‐
     sions will extract the metadata into regular files, where the metadata
     can be examined as necessary.

     An entry in a pax interchange format archive consists of one or two stan‐
     dard ustar entries, each with its own header and data.  The first
     optional entry stores the extended attributes for the following entry.
     This optional first entry has an "x" typeflag and a size field that indi‐
     cates the total size of the extended attributes.  The extended attributes
     themselves are stored as a series of text-format lines encoded in the
     portable UTF-8 encoding.  Each line consists of a decimal number, a
     space, a key string, an equals sign, a value string, and a new line.  The
     decimal number indicates the length of the entire line, including the
     initial length field and the trailing newline.  An example of such a
     field is:
	   25 ctime=1084839148.1212\n
     Keys in all lowercase are standard keys.  Vendors can add their own keys
     by prefixing them with an all uppercase vendor name and a period.	Note
     that, unlike the historic header, numeric values are stored using deci‐
     mal, not octal.  A description of some common keys follows:

     1matime22m, 1mctime22m, 1mmtime0m
	     File access, inode change, and modification times.  These fields
	     can be negative or include a decimal point and a fractional
	     value.

     1mhdrcharset0m
	     The character set used by the pax extension values.  By default,
	     all textual values in the pax extended attributes are assumed to
	     be in UTF-8, including pathnames, user names, and group names.
	     In some cases, it is not possible to translate local conventions
	     into UTF-8.  If this key is present and the value is the six-
	     character ASCII string “BINARY”, then all textual values are
	     assumed to be in a platform-dependent multi-byte encoding.  Note
	     that there are only two valid values for this key: “BINARY” or
	     “ISO-IR 10646 2000 UTF-8”.  No other values are permitted by the
	     standard, and the latter value should generally not be used as it
	     is the default when this key is not specified.  In particular,
	     this flag should not be used as a general mechanism to allow
	     filenames to be stored in arbitrary encodings.

     1muname22m, 1muid22m, 1mgname22m, 1mgid0m
	     User name, group name, and numeric UID and GID values.  The user
	     name and group name stored here are encoded in UTF8 and can thus
	     include non-ASCII characters.  The UID and GID fields can be of
	     arbitrary length.

     1mlinkpath0m
	     The full path of the linked-to file.  Note that this is encoded
	     in UTF8 and can thus include non-ASCII characters.

     1mpath    22mThe full pathname of the entry.  Note that this is encoded in
	     UTF8 and can thus include non-ASCII characters.

     1mrealtime.*22m, 1msecurity.*0m
	     These keys are reserved and may be used for future standardiza‐
	     tion.

     1msize    22mThe size of the file.  Note that there is no length limit on this
	     field, allowing conforming archives to store files much larger
	     than the historic 8GB limit.

     1mSCHILY.*0m
	     Vendor-specific attributes used by Joerg Schilling's 1mstar 22mimple‐
	     mentation.

     1mSCHILY.acl.access22m, 1mSCHILY.acl.default, SCHILY.acl.ace0m
	     Stores the access, default and NFSv4 ACLs as textual strings in a
	     format that is an extension of the format specified by POSIX.1e
	     draft 17.	In particular, each user or group access specification
	     can include an additional colon-separated field with the numeric
	     UID or GID.  This allows ACLs to be restored on systems that may
	     not have complete user or group information available (such as
	     when NIS/YP or LDAP services are temporarily unavailable).

     1mSCHILY.devminor22m, 1mSCHILY.devmajor0m
	     The full minor and major numbers for device nodes.

     1mSCHILY.fflags0m
	     The file flags.

     1mSCHILY.realsize0m
	     The full size of the file on disk.  XXX explain? XXX

     1mSCHILY.dev, SCHILY.ino22m, 1mSCHILY.nlinks0m
	     The device number, inode number, and link count for the entry.
	     In particular, note that a pax interchange format archive using
	     Joerg Schilling's 1mSCHILY.* 22mextensions can store all of the data
	     from 4mstruct24m 4mstat24m.

     1mLIBARCHIVE.*0m
	     Vendor-specific attributes used by the 1mlibarchive 22mlibrary and
	     programs that use it.

     1mLIBARCHIVE.creationtime0m
	     The time when the file was created.  (This should not be confused
	     with the POSIX “ctime” attribute, which refers to the time when
	     the file metadata was last changed.)

     1mLIBARCHIVE.xattr.4m22mnamespace24m.4mkey0m
	     Libarchive stores POSIX.1e-style extended attributes using keys
	     of this form.  The 4mkey24m value is URL-encoded: All non-ASCII char‐
	     acters and the two special characters “=” and “%” are encoded as
	     “%” followed by two uppercase hexadecimal digits.	The value of
	     this key is the extended attribute value encoded in base 64.  XXX
	     Detail the base-64 format here XXX

     1mVENDOR.*0m
	     XXX document other vendor-specific extensions XXX

     Any values stored in an extended attribute override the corresponding
     values in the regular tar header.	Note that compliant readers should
     ignore the regular fields when they are overridden.  This is important,
     as existing archivers are known to store non-compliant values in the
     standard header fields in this situation.	There are no limits on length
     for any of these fields.  In particular, numeric fields can be arbitrar‐
     ily large.  All text fields are encoded in UTF8.  Compliant writers
     should store only portable 7-bit ASCII characters in the standard ustar
     header and use extended attributes whenever a text value contains non-
     ASCII characters.

     In addition to the 1mx 22mentry described above, the pax interchange format
     also supports a 1mg 22mentry.  The 1mg 22mentry is identical in format, but speci‐
     fies attributes that serve as defaults for all subsequent archive
     entries.  The 1mg 22mentry is not widely used.

     Besides the new 1mx 22mand 1mg 22mentries, the pax interchange format has a few
     other minor variations from the earlier ustar format.  The most troubling
     one is that hardlinks are permitted to have data following them.  This
     allows readers to restore any hardlink to a file without having to rewind
     the archive to find an earlier entry.  However, it creates complications
     for robust readers, as it is no longer clear whether or not they should
     ignore the size field for hardlink entries.

   1mGNU Tar Archives0m
     The GNU tar program started with a pre-POSIX format similar to that
     described earlier and has extended it using several different mechanisms:
     It added new fields to the empty space in the header (some of which was
     later used by POSIX for conflicting purposes); it allowed the header to
     be continued over multiple records; and it defined new entries that mod‐
     ify following entries (similar in principle to the 1mx 22mentry described
     above, but each GNU special entry is single-purpose, unlike the general-
     purpose 1mx 22mentry).  As a result, GNU tar archives are not POSIX compati‐
     ble, although more lenient POSIX-compliant readers can successfully
     extract most GNU tar archives.

	   struct header_gnu_tar {
		   char name[100];
		   char mode[8];
		   char uid[8];
		   char gid[8];
		   char size[12];
		   char mtime[12];
		   char checksum[8];
		   char typeflag[1];
		   char linkname[100];
		   char magic[6];
		   char version[2];
		   char uname[32];
		   char gname[32];
		   char devmajor[8];
		   char devminor[8];
		   char atime[12];
		   char ctime[12];
		   char offset[12];
		   char longnames[4];
		   char unused[1];
		   struct {
			   char offset[12];
			   char numbytes[12];
		   } sparse[4];
		   char isextended[1];
		   char realsize[12];
		   char pad[17];
	   };

     4mtypeflag0m
	     GNU tar uses the following special entry types, in addition to
	     those defined by POSIX:

	     7	     GNU tar treats type "7" records identically to type "0"
		     records, except on one obscure RTOS where they are used
		     to indicate the pre-allocation of a contiguous file on
		     disk.

	     D	     This indicates a directory entry.	Unlike the POSIX-stan‐
		     dard "5" typeflag, the header is followed by data records
		     listing the names of files in this directory.  Each name
		     is preceded by an ASCII "Y" if the file is stored in this
		     archive or "N" if the file is not stored in this archive.
		     Each name is terminated with a null, and an extra null
		     marks the end of the name list.  The purpose of this
		     entry is to support incremental backups; a program
		     restoring from such an archive may wish to delete files
		     on disk that did not exist in the directory when the ar‐
		     chive was made.

		     Note that the "D" typeflag specifically violates POSIX,
		     which requires that unrecognized typeflags be restored as
		     normal files.  In this case, restoring the "D" entry as a
		     file could interfere with subsequent creation of the
		     like-named directory.

	     K	     The data for this entry is a long linkname for the fol‐
		     lowing regular entry.

	     L	     The data for this entry is a long pathname for the fol‐
		     lowing regular entry.

	     M	     This is a continuation of the last file on the previous
		     volume.  GNU multi-volume archives guarantee that each
		     volume begins with a valid entry header.  To ensure this,
		     a file may be split, with part stored at the end of one
		     volume, and part stored at the beginning of the next vol‐
		     ume.  The "M" typeflag indicates that this entry contin‐
		     ues an existing file.  Such entries can only occur as the
		     first or second entry in an archive (the latter only if
		     the first entry is a volume label).  The 4msize24m field spec‐
		     ifies the size of this entry.  The 4moffset24m field at bytes
		     369-380 specifies the offset where this file fragment
		     begins.  The 4mrealsize24m field specifies the total size of
		     the file (which must equal 4msize24m plus 4moffset24m).  When
		     extracting, GNU tar checks that the header file name is
		     the one it is expecting, that the header offset is in the
		     correct sequence, and that the sum of offset and size is
		     equal to realsize.

	     N	     Type "N" records are no longer generated by GNU tar.
		     They contained a list of files to be renamed or symlinked
		     after extraction; this was originally used to support
		     long names.  The contents of this record are a text
		     description of the operations to be done, in the form
		     “Rename %s to %s\n” or “Symlink %s to %s\n”; in either
		     case, both filenames are escaped using K&R C syntax.  Due
		     to security concerns, "N" records are now generally
		     ignored when reading archives.

	     S	     This is a “sparse” regular file.  Sparse files are stored
		     as a series of fragments.	The header contains a list of
		     fragment offset/length pairs.  If more than four such
		     entries are required, the header is extended as necessary
		     with “extra” header extensions (an older format that is
		     no longer used), or “sparse” extensions.

	     V	     The 4mname24m field should be interpreted as a tape/volume
		     header name.  This entry should generally be ignored on
		     extraction.

     4mmagic24m   The magic field holds the five characters “ustar” followed by a
	     space.  Note that POSIX ustar archives have a trailing null.

     4mversion0m
	     The version field holds a space character followed by a null.
	     Note that POSIX ustar archives use two copies of the ASCII digit
	     “0”.

     4matime24m, 4mctime0m
	     The time the file was last accessed and the time of last change
	     of file information, stored in octal as with 4mmtime24m.

     4mlongnames0m
	     This field is apparently no longer used.

     Sparse 4moffset24m 4m/24m 4mnumbytes0m
	     Each such structure specifies a single fragment of a sparse file.
	     The two fields store values as octal numbers.  The fragments are
	     each padded to a multiple of 512 bytes in the archive.  On
	     extraction, the list of fragments is collected from the header
	     (including any extension headers), and the data is then read and
	     written to the file at appropriate offsets.

     4misextended0m
	     If this is set to non-zero, the header will be followed by addi‐
	     tional “sparse header” records.  Each such record contains infor‐
	     mation about as many as 21 additional sparse blocks as shown
	     here:

		   struct gnu_sparse_header {
			   struct {
				   char offset[12];
				   char numbytes[12];
			   } sparse[21];
			   char    isextended[1];
			   char    padding[7];
		   };

     4mrealsize0m
	     A binary representation of the file's complete size, with a much
	     larger range than the POSIX file size.  In particular, with 1mM0m
	     type files, the current entry is only a portion of the file.  In
	     that case, the POSIX size field will indicate the size of this
	     entry; the 4mrealsize24m field will indicate the total size of the
	     file.

   1mGNU tar pax archives0m
     GNU tar 1.14 (XXX check this XXX) and later will write pax interchange
     format archives when you specify the 1m--posix 22mflag.  This format follows
     the pax interchange format closely, using some 1mSCHILY 22mtags and introduc‐
     ing new keywords to store sparse file information.  There have been three
     iterations of the sparse file support, referred to as “0.0”, “0.1”, and
     “1.0”.

     1mGNU.sparse.numblocks22m, 1mGNU.sparse.offset22m, 1mGNU.sparse.numbytes22m,
	     1mGNU.sparse.size0m
	     The “0.0” format used an initial 1mGNU.sparse.numblocks 22mattribute
	     to indicate the number of blocks in the file, a pair of
	     1mGNU.sparse.offset 22mand 1mGNU.sparse.numbytes 22mto indicate the offset
	     and size of each block, and a single 1mGNU.sparse.size 22mto indicate
	     the full size of the file.  This is not the same as the size in
	     the tar header because the latter value does not include the size
	     of any holes.  This format required that the order of attributes
	     be preserved and relied on readers accepting multiple appearances
	     of the same attribute names, which is not officially permitted by
	     the standards.

     1mGNU.sparse.map0m
	     The “0.1” format used a single attribute that stored a comma-sep‐
	     arated list of decimal numbers.  Each pair of numbers indicated
	     the offset and size, respectively, of a block of data.  This does
	     not work well if the archive is extracted by an archiver that
	     does not recognize this extension, since many pax implementations
	     simply discard unrecognized attributes.

     1mGNU.sparse.major22m, 1mGNU.sparse.minor22m, 1mGNU.sparse.name22m, 1mGNU.sparse.realsize0m
	     The “1.0” format stores the sparse block map in one or more
	     512-byte blocks prepended to the file data in the entry body.
	     The pax attributes indicate the existence of this map (via the
	     1mGNU.sparse.major 22mand 1mGNU.sparse.minor 22mfields) and the full size
	     of the file.  The 1mGNU.sparse.name 22mholds the true name of the
	     file.  To avoid confusion, the name stored in the regular tar
	     header is a modified name so that extraction errors will be
	     apparent to users.

   1mSolaris Tar0m
     XXX More Details Needed XXX

     Solaris tar (beginning with SunOS XXX 5.7 ?? XXX) supports an “extended”
     format that is fundamentally similar to pax interchange format, with the
     following differences:
     1m·       22mExtended attributes are stored in an entry whose type is 1mX22m, not
	     1mx22m, as used by pax interchange format.  The detailed format of
	     this entry appears to be the same as detailed above for the 1mx0m
	     entry.
     1m·       22mAn additional 1mA 22mheader is used to store an ACL for the following
	     regular entry.  The body of this entry contains a seven-digit
	     octal number followed by a zero byte, followed by the textual ACL
	     description.  The octal value is the number of ACL entries plus a
	     constant that indicates the ACL type: 01000000 for POSIX.1e ACLs
	     and 03000000 for NFSv4 ACLs.

   1mAIX Tar0m
     XXX More details needed XXX

     AIX Tar uses a ustar-formatted header with the type 1mA 22mfor storing coded
     ACL information.  Unlike the Solaris format, AIX tar writes this header
     after the regular file body to which it applies.  The pathname in this
     header is either 1mNFS4 22mor 1mAIXC 22mto indicate the type of ACL stored.  The
     actual ACL is stored in platform-specific binary format.

   1mMac OS X Tar0m
     The tar distributed with Apple's Mac OS X stores most regular files as
     two separate files in the tar archive.  The two files have the same name
     except that the first one has “._” prepended to the last path element.
     This special file stores an AppleDouble-encoded binary blob with addi‐
     tional metadata about the second file, including ACL, extended
     attributes, and resources.  To recreate the original file on disk, each
     separate file can be extracted and the Mac OS X 1mcopyfile22m() function can
     be used to unpack the separate metadata file and apply it to th regular
     file.  Conversely, the same function provides a “pack” option to encode
     the extended metadata from a file into a separate file whose contents can
     then be put into a tar archive.

     Note that the Apple extended attributes interact badly with long file‐
     names.  Since each file is stored with the full name, a separate set of
     extensions needs to be included in the archive for each one, doubling the
     overhead required for files with long names.

   1mSummary of tar type codes0m
     The following list is a condensed summary of the type codes used in tar
     header records generated by different tar implementations.  More details
     about specific implementations can be found above:
     NUL  Early tar programs stored a zero byte for regular files.
     1m0    22mPOSIX standard type code for a regular file.
     1m1    22mPOSIX standard type code for a hard link description.
     1m2    22mPOSIX standard type code for a symbolic link description.
     1m3    22mPOSIX standard type code for a character device node.
     1m4    22mPOSIX standard type code for a block device node.
     1m5    22mPOSIX standard type code for a directory.
     1m6    22mPOSIX standard type code for a FIFO.
     1m7    22mPOSIX reserved.
     1m7    22mGNU tar used for pre-allocated files on some systems.
     1mA    22mSolaris tar ACL description stored prior to a regular file header.
     1mA    22mAIX tar ACL description stored after the file body.
     1mD    22mGNU tar directory dump.
     1mK    22mGNU tar long linkname for the following header.
     1mL    22mGNU tar long pathname for the following header.
     1mM    22mGNU tar multivolume marker, indicating the file is a continuation of
	  a file from the previous volume.
     1mN    22mGNU tar long filename support.  Deprecated.
     1mS    22mGNU tar sparse regular file.
     1mV    22mGNU tar tape/volume header name.
     1mX    22mSolaris tar general-purpose extension header.
     1mg    22mPOSIX pax interchange format global extensions.
     1mx    22mPOSIX pax interchange format per-file extensions.

1mSEE ALSO0m
     ar(1), pax(1), tar(1)

1mSTANDARDS0m
     The 1mtar 22mutility is no longer a part of POSIX or the Single Unix Standard.
     It last appeared in Version 2 of the Single UNIX Specification (“SUSv2”).
     It has been supplanted in subsequent standards by pax(1).	The ustar for‐
     mat is currently part of the specification for the pax(1) utility.  The
     pax interchange file format is new with IEEE Std 1003.1-2001 (“POSIX.1”).

1mHISTORY0m
     A 1mtar 22mcommand appeared in Seventh Edition Unix, which was released in
     January, 1979.  It replaced the 1mtp 22mprogram from Fourth Edition Unix which
     in turn replaced the 1mtap 22mprogram from First Edition Unix.  John Gilmore's
     1mpdtar 22mpublic-domain implementation (circa 1987) was highly influential
     and formed the basis of 1mGNU tar 22m(circa 1988).  Joerg Shilling's 1mstar0m
     archiver is another open-source (CDDL) archiver (originally developed
     circa 1985) which features complete support for pax interchange format.

     This documentation was written as part of the 1mlibarchive 22mand 1mbsdtar0m
     project by Tim Kientzle <kientzle@FreeBSD.org>.

BSD			       December 27, 2016			   BSD
