z/OS V1R9.0 UNIX System Services Command ... - Christian Grothoff

USTAR format. The extended USTAR format allows more information to be stored
and supports longer pathnames. There is also a non-portable OS390 format (–S
option) which also allows storing of additional file attributes and longer pathnames.
A tar archive, in either format, consists of one or more blocks, which are used to
represent member files. Each block is 512 bytes long; you can use the –b option
with tar to indicate how many of these blocks are read or written (or both) at once.
Each member file consists of a header block, followed by zero or more blocks
containing the file contents. The end of the archive is indicated by two blocks filled
with binary zeros. Unused space in the header is left as binary zeros.
The header information in a block is stored in a printable ASCII form, so that tar
archives are easily ported to different environments. If the contents of the files on
the archive are all ASCII, the entire archive is ASCII.
Table 42 shows the UNIX format of the header block for a file:
Table 42. Archive File: UNIX-Compatible Format
Field Width Field Name Meaning
100 name Name of file
8 mode File mode
8 uid Owner user ID
8 gid Owner group ID
12 size Length of file in bytes
12 mtime Modify time of file
8 chksum Checksum for header
1 link Indicator for links
100 linkname Name of linked file
v A directory is indicated by a trailing /(slash) in its name.
v The link field is: 1 for a linked file, 2 for a symbolic link, 0 otherwise.
tar determines that the USTAR format is being used by the presence of the
null-terminated string USTAR in the magic field. All fields before the magic field
correspond to those of the UNIX format, except that typeflag replaces the link field.
Table 43. Archive File: USTAR Format
Field Width Field Name Meaning
100 name Name of file
8 mode File mode
8 uid Owner user ID
8 gid Owner group ID
12 size Length of file in bytes
12 mtime Modify time of file
8 chksum Checksum for header
1 typeflag Type of file
100 linkname Name of linked file
6 magic USTAR indicator
2 version USTAR version
32 uname Owner user name
32 gname Owner group name
8 devmajor Device major number
8 devminor Device minor number
155 prefix Prefix for filename
tar
Appendix H. File Formats 923