tar(F)                          19 June 1992                          tar(F)


 Name

    tar - archive format

 Description

    The command tar(C) dumps files to, and extracts files from, backup media
    or the hard disk.

    Each file is archived in contiguous blocks.  The first block is occupied
    by a header, whose format is given below, and the subsequent blocks of
    the files occupy the following blocks.  All headers and file data start
    on 512-byte block boundaries and any extra unused space is padded with
    garbage. The format of a header block is as follows:

       #define TBLOCK 512
       #define NBLOCK 20
       #define NAMSIZ 100
       union hblock {
               char dummy[TBLOCK];
               struct header {
                       char name[NAMSIZ];
                       char mode[8];
                       char uid[8];
                       char gid[8];
                       char size[12];
                       char mtime[12];
                       char chksum[8];
                       char linkflag;
                       char linkname[NAMSIZ];
                       char extno[4];
                       char extotal[4];
                       char efsize[12];
               } dbuf;
       } dblock;

    The name entry is the pathname of the file when archived. If the pathname
    starts with a zero word, the entry is empty.  It is a maximum of 100
    bytes long and ends in a null byte. mode, uid, gid, size, and time modi-
    fied are the same as described under i-nodes (refer to filesystem(FP)).
    The checksum entry has a value such that the sum of the words of the
    directory entry is zero.

    If the entry corresponds to a link, then linkname contains the pathname
    of the file to which this entry is linked; linkflag is set to 0 if there
    are no links, or 1 if there are links.  No data is put in the archive
    file.

 See also

    filesystem(FP), tar(C)

 Standards conformance

    tar is conformant with:

    AT&T SVID Issue 2.