diff options
Diffstat (limited to 'libarchive/tar.5')
| -rw-r--r-- | libarchive/tar.5 | 198 |
1 files changed, 157 insertions, 41 deletions
diff --git a/libarchive/tar.5 b/libarchive/tar.5 index 143d350..65875bd 100644 --- a/libarchive/tar.5 +++ b/libarchive/tar.5 @@ -171,9 +171,9 @@ These archives generally follow the POSIX ustar format described below with the following variations: .Bl -bullet -compact -width indent .It -The magic value is -.Dq ustar\ \& -(note the following space). +The magic value consists of the five characters +.Dq ustar +followed by a space. The version field contains a space character followed by a null. .It The numeric fields are generally filled with leading spaces @@ -322,6 +322,39 @@ characters. Currently, most tar implementations comply with the ustar format, occasionally extending it by adding new fields to the blank area at the end of the header record. +.Ss Numeric Extensions +There have been several attempts to extend the range of sizes +or times supported by modifying how numbers are stored in the +header. +.Pp +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. +.Pp +Another extension, utilized by GNU tar, star, and other newer +.Nm +implementations, 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 program 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. +.Pp +Another early GNU extension allowed base-64 values rather than octal. +This extension was short-lived and is no longer supported by any +implementation. .Ss Pax Interchange Format There are many attributes that cannot be portably stored in a POSIX ustar archive. @@ -365,6 +398,27 @@ A description of some common keys follows: .It Cm atime , Cm ctime , Cm mtime File access, inode change, and modification times. These fields can be negative or include a decimal point and a fractional value. +.It Cm hdrcharset +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 +.Dq 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: +.Dq BINARY +or +.Dq 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. .It Cm uname , Cm uid , Cm gname , Cm gid User name, group name, and numeric UID and GID values. The user name and group name stored here are encoded in UTF8 @@ -408,6 +462,16 @@ Schilling's .Cm SCHILY.* extensions can store all of the data from .Va struct stat . +.It Cm LIBARCHIVE.* +Vendor-specific attributes used by the +.Nm libarchive +library and programs that use it. +.It Cm LIBARCHIVE.creationtime +The time when the file was created. +(This should not be confused with the POSIX +.Dq ctime +attribute, which refers to the time when the file +metadata was last changed.) .It Cm LIBARCHIVE.xattr. Ns Ar namespace Ns . Ns Ar key Libarchive stores POSIX.1e-style extended attributes using keys of this form. @@ -659,8 +723,11 @@ GNU tar 1.14 (XXX check this XXX) and later will write pax interchange format archives when you specify the .Fl -posix flag. -This format uses custom keywords to store sparse file information. -There have been three iterations of this support, referred to +This format follows the pax interchange format closely, +using some +.Cm SCHILY +tags and introducing new keywords to store sparse file information. +There have been three iterations of the sparse file support, referred to as .Dq 0.0 , .Dq 0.1 , @@ -735,7 +802,7 @@ entry. .It An additional .Cm A -entry is used to store an ACL for the following regular entry. +header 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. @@ -745,46 +812,95 @@ for POSIX.1e ACLs and 03000000 for NFSv4 ACLs. .El .Ss AIX Tar XXX More details needed XXX +.Pp +AIX Tar uses a ustar-formatted header with the type +.Cm A +for 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 +.Cm NFS4 +or +.Cm AIXC +to indicate the type of ACL stored. +The actual ACL is stored in platform-specific binary format. .Ss Mac OS X Tar The tar distributed with Apple's Mac OS X stores most regular files -as two separate entries in the tar archive. -The two entries have the same name except that the first +as two separate files in the tar archive. +The two files have the same name except that the first one has .Dq ._ -added to the beginning of the name. -This first entry stores the -.Dq resource fork -with additional attributes for the file. -The Mac OS X -.Fn CopyFile -API is used to separate a file on disk into separate -resource and data streams and to reassemble those separate -streams when the file is restored to disk. -.Ss Other Extensions -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. -.Pp -Another extension, utilized by GNU tar, star, and other newer -.Nm -implementations, permits binary numbers in the standard numeric fields. -This is flagged by setting the high bit of the first byte. -This permits 95-bit values for the length and time fields -and 63-bit values for the uid, gid, and device numbers. -GNU tar supports this extension for the -length, mtime, ctime, and atime fields. -Joerg Schilling's star program supports this extension for -all numeric fields. -Note that this extension is largely obsoleted by the extended attribute -record provided by the pax interchange format. +prepended to the last path element. +This special file stores an AppleDouble-encoded +binary blob with additional 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 +.Fn copyfile +function can be used to unpack the separate +metadata file and apply it to th regular file. +Conversely, the same function provides a +.Dq pack +option to encode the extended metadata from +a file into a separate file whose contents +can then be put into a tar archive. .Pp -Another early GNU extension allowed base-64 values rather than octal. -This extension was short-lived and is no longer supported by any -implementation. +Note that the Apple extended attributes interact +badly with long filenames. +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. +.Ss Summary of tar type codes +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: +.Bl -tag -compact -width XXX +.It NUL +Early tar programs stored a zero byte for regular files. +.It Cm 0 +POSIX standard type code for a regular file. +.It Cm 1 +POSIX standard type code for a hard link description. +.It Cm 2 +POSIX standard type code for a symbolic link description. +.It Cm 3 +POSIX standard type code for a character device node. +.It Cm 4 +POSIX standard type code for a block device node. +.It Cm 5 +POSIX standard type code for a directory. +.It Cm 6 +POSIX standard type code for a FIFO. +.It Cm 7 +POSIX reserved. +.It Cm 7 +GNU tar used for pre-allocated files on some systems. +.It Cm A +Solaris tar ACL description stored prior to a regular file header. +.It Cm A +AIX tar ACL description stored after the file body. +.It Cm D +GNU tar directory dump. +.It Cm K +GNU tar long linkname for the following header. +.It Cm L +GNU tar long pathname for the following header. +.It Cm M +GNU tar multivolume marker, indicating the file is a continuation of a file from the previous volume. +.It Cm N +GNU tar long filename support. Deprecated. +.It Cm S +GNU tar sparse regular file. +.It Cm V +GNU tar tape/volume header name. +.It Cm X +Solaris tar general-purpose extension header. +.It Cm g +POSIX pax interchange format global extensions. +.It Cm x +POSIX pax interchange format per-file extensions. +.El .Sh SEE ALSO .Xr ar 1 , .Xr pax 1 , |
