/*
* Standard Archive Format - Standard TAR - USTAR
*/
#define RECORDSIZE 512
#define NAMSIZ 100
#define TUNMLEN 32
#define TGNMLEN 32
union record {
char charptr[RECORDSIZE];
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 magic[8];
char uname[TUNMLEN];
char gname[TGNMLEN];
char devmajor[8];
char devminor[8];
} header;
};
/* The checksum field is filled with this while the checksum is computed. */
#define CHKBLANKS " " /* 8 blanks, no null */
/* The magic field is filled with this if uname and gname are valid. */
#define TMAGIC "ustar " /* 7 chars and a null */
/* The linkflag defines the type of file */
#define LF_OLDNORMAL '\0' /* Normal disk file, Unix compatible */
#define LF_NORMAL '0' /* Normal disk file */
#define LF_LINK '1' /* Link to previously dumped file */
#define LF_SYMLINK '2' /* Symbolic link */
#define LF_CHR '3' /* Character special file */
#define LF_BLK '4' /* Block special file */
#define LF_DIR '5' /* Directory */
#define LF_FIFO '6' /* FIFO special file */
#define LF_CONTIG '7' /* Contiguous file */
/* Further link types may be defined later. */
/* Bits used in the mode field - values in octal */
#define TSUID 04000 /* Set UID on execution */
#define TSGID 02000 /* Set GID on execution */
#define TSVTX 01000 /* Save text (sticky bit) */
/* File permissions */
#define TUREAD 00400 /* read by owner */
#define TUWRITE 00200 /* write by owner */
#define TUEXEC 00100 /* execute/search by owner */
#define TGREAD 00040 /* read by group */
#define TGWRITE 00020 /* write by group */
#define TGEXEC 00010 /* execute/search by group */
#define TOREAD 00004 /* read by other */
#define TOWRITE 00002 /* write by other */
#define TOEXEC 00001 /* execute/search by other */
All characters in header records are represented using 8-bit characters in the local variant of ASCII. Each field within the structure is contiguous; that is, there is no padding used within the structure. Each character on the archive medium is stored contiguously. Bytes representing the contents of files (after the header record of each file) are not translated in any way and are not constrained to represent characters or to be in any character set. The tar(5) format does not distinguish text files from binary files, and no translation of file contents should be performed. The fields name, linkname, magic, uname, and gname are null-terminated character strings. All other fields are zero-filled octal numbers in ASCII. Each numeric field (of width w) contains w-2 digits, a space, and a null, except size and mtime, which do not contain the trailing null. The name field is the pathname of the file, with directory names (if any) preceding the file name, separated by slashes. The mode field provides nine bits specifying file permissions and three bits to specify the Set UID, Set GID and Save Text (TSVTX) modes. Values for these bits are defined above. When special permissions are required to create a file with a given mode, and the user restoring files from the archive does not hold such permissions, the mode bit(s) specifying those special permissions are ignored. Modes which are not supported by the operating system restoring files from the archive will be ignored. Unsupported modes should be faked up when creating an archive; e.g. the group permission could be copied from the `other' permission. The uid and gid fields are the user and group ID of the file owners, respectively. The size field is the size of the file in bytes; linked files are archived with this field specified as zero. The mtime field is the modification time of the file at the time it was archived. It is the ASCII representation of the octal value of the last time the file was modified, represented as in integer number of seconds since January 1, 1970, 00:00 Coordinated Universal Time. The chksum field is the ASCII representaion of the octal value of the simple sum of all bytes in the header record. Each 8-bit byte in the header is treated as an unsigned value. These values are added to an unsigned integer, initialized to zero, the precision of which shall be no less than seventeen bits. When calculating the checksum, the chksum field is treated as if it were all blanks. The typeflag field specifies the type of file archived. If a particular implementation does not recognize or permit the specified type, the file will be extracted as if it were a regular file. As this action occurs, tar issues a warning to the standard error.
The magic field indicates that this archive was output in the P1003 archive format. If this field contains TMAGIC, then the uname and gname fields will contain the ASCII representation of the owner and group of the file respectively. If found, the user and group ID represented by these names will be used rather than the values contained within the uid and gid fields. User names longer than TUNMLEN-1 or group names longer than TGNMLEN-1 characters will be truncated.