TAR(5)
NAME
tar − tape archive format
DESCRIPTION
The tar command dumps files to and extracts files from magtape in tape archive format. Unlike tp tapes, tar tapes have no provision for a bootstrap program. The record size for tar tapes is always a multiple of 512 bytes. The most common blocking factors are one and 20.
Tape archive format consists of a header record followed by the contents of the file. The header record has the following structure:
#define TBLOCK512
#define NBLOCK20
#define NAMSIZ100
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 rdev[6];/* file type */
} dbuf;
} dblock, tbuf[NBLOCK];