tar

Purpose

     Describes the tape archive format.

Description

     The tar  command reads and  writes tapes in  tape archive
     format.  A tar tape  consists of several 512-byte logical
     blocks  that  can  be  grouped (on  magnetic  tape)  into
     records,  which are  some constant  multiple of  512-byte
     blocks long.   Block in  the following  description means
     logical block.

     The following  is the format  of a file header  that pre-
     cedes each disk file written on the tape:

          struct {
               char name[100];
               char mode[8];
               char uid[8];
               char gid[8];
               char size[12];
               char mtime[12];
               char chksum[8];
               char linkflag;
               char linkname[100];
          };

     All  fields, except  linkflag, are  ASCII null-terminated
     strings.  Numeric fields can contain leading blanks.  The
     fields have the following meanings:

     chksum     Contains  a  byte-by-byte  sum of  the  entire
                header block assuming that the chksum field is
                all blanks.

     gid        Contains the group identification of the file,
                in octal.

     linkflag   Contains a 1 if this file  is a link to a pre-
                vious file on the the tape, otherwise null.

     linkname   Contains the name of a  file if linkflag has a
                value of 1.   The file named in  this field is
                linked to the name file.

     mode       Contains the mode of  the file, which includes
                the protection bits, setuid bits, setgid bits,
                and file type, in octal.

     mtime      Contains  the  modification  time,  in  octal.
                This field gives the major/minor device number
                for special files.

     name       Contains the name of the file.

     size       Contains the  size in  bytes, in  octal.  This
                field is 0 for special files.

     uid        Contains the user  identification of the file,
                in octal.

     Unused bytes  are null.  Following the  file header block
     are the data blocks of the file.  The last block is null-
     padded if  necessary.  Two null blocks  designate the end
     of the tape.

     Directories and  special files are treated  in a slightly
     different way.   A directory size  is 0, meaning  no data
     blocks follow,  and its  name ends with  a /  (slash).  A
     special  file   is  also   written  with  0   size.   Its
     major/minor device number is in the mtime field.

Related Information

     The tar  command in AIX Operating  System Commands Refer-
     ence.