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Text File | 1990-04-01 | 13.6 KB | 330 lines

TTTTAAAARRRR((((5555)))) AAAAmmmmiiiiggggaaaaDDDDOOOOSSSS ((((11115555 OOOOccccttttoooobbbbeeeerrrr 1111999988887777)))) TTTTAAAARRRR((((5555)))) NNNNAAAAMMMMEEEE tar - tape (or other media) archive file format DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN A ``tar tape'' or file contains a series of records. Each record contains TRECORDSIZE bytes (see below). Although this format may be thought of as being on magnetic tape, other media are often used. Each file archived is represented by a header record which describes the file, followed by zero or more records which give the contents of the file. At the end of the archive file there may be a record filled with binary zeros as an end-of-file indicator. A reasonable system should write a record of zeros at the end, but must not assume that an end-of-file record exists when reading an archive. The records may be blocked for physical I/O operations. Each block of _N records (where _N is set by the ----bbbb option to _t_a_r) is written with a single write() operation. On magnetic tapes, the result of such a write is a single tape record. When writing an archive, the last block of records should be written at the full size, with records after the zero record containing all zeroes. When reading an archive, a reasonable system should properly handle an archive whose last block is shorter than the rest, or which contains garbage records after a zero record. The header record is defined in the header file <tar.h> as follows: /* * 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]; Page 1 (printed 3/8/90) TTTTAAAARRRR((((5555)))) AAAAmmmmiiiiggggaaaaDDDDOOOOSSSS ((((11115555 OOOOccccttttoooobbbbeeeerrrr 1111999988887777)))) TTTTAAAARRRR((((5555)))) 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 _t_a_r(5) format does not distinguish text files from binary files, and no translation of file contents should be performed. Page 2 (printed 3/8/90) TTTTAAAARRRR((((5555)))) AAAAmmmmiiiiggggaaaaDDDDOOOOSSSS ((((11115555 OOOOccccttttoooobbbbeeeerrrr 1111999988887777)))) TTTTAAAARRRR((((5555)))) The fields _n_a_m_e, _l_i_n_k_n_a_m_e, _m_a_g_i_c, _u_n_a_m_e, and _g_n_a_m_e 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 _s_i_z_e and _m_t_i_m_e, which do not contain the trailing null. The _n_a_m_e field is the pathname of the file, with directory names (if any) preceding the file name, separated by slashes. The _m_o_d_e 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 _u_i_d and _g_i_d fields are the user and group ID of the file owners, respectively. The _s_i_z_e field is the size of the file in bytes; linked files are archived with this field specified as zero. The _m_t_i_m_e 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 _c_h_k_s_u_m 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 _c_h_k_s_u_m field is treated as if it were all blanks. The _t_y_p_e_f_l_a_g 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, _t_a_r issues a warning to the standard error. LF_NORMAL or LF_OLDNORMAL represents a regular file. For backward compatibility, a _t_y_p_e_f_l_a_g value of LF_OLDNORMAL should be silently Page 3 (printed 3/8/90) TTTTAAAARRRR((((5555)))) AAAAmmmmiiiiggggaaaaDDDDOOOOSSSS ((((11115555 OOOOccccttttoooobbbbeeeerrrr 1111999988887777)))) TTTTAAAARRRR((((5555)))) recognized as a regular file. New archives should be created using LF_NORMAL. Also, for backward compatability, _t_a_r treats a regular file whose name ends with a slash as a directory. LF_LINK represents a file linked to another file, of any type, previously archived. Such files are identified in Unix by each file having the same device and inode number. The linked-to name is specified in the _l_i_n_k_n_a_m_e field with a trailing null. LF_SYMLINK represents a symbolic link to another file. The linked-to name is specified in the _l_i_n_k_n_a_m_e field with a trailing null. LF_CHR or LF_BLK represent character special files and block special files respectively. In this case the _d_e_v_m_a_j_o_r and _d_e_v_m_i_n_o_r fields will contain the major and minor device numbers respectively. Operating systems may map the device specifications to their own local specification, or may ignore the entry. LF_DIR specifies a directory or sub-directory. The directory name in the _n_a_m_e field should end with a slash. On systems where disk allocation is performed on a directory basis the _s_i_z_e field will contain the maximum number of bytes (which may be rounded to the nearest disk block allocation unit) which the directory may hold. A _s_i_z_e field of zero indicates no such limiting. Systems which do not support limiting in this manner should ignore the _s_i_z_e field. LF_FIFO specifies a FIFO special file. Note that the archiving of a FIFO file archives the existence of this file and not its contents. LF_CONTIG specifies a contiguous file, which is the same as a normal file except that, in operating systems which support it, all its space is allocated contiguously on the disk. Operating systems which do not allow contiguous allocation should silently treat this type as a normal file. `A' - `Z' are reserved for custom implementations. None are used by this version of the _t_a_r program. Page 4 (printed 3/8/90) TTTTAAAARRRR((((5555)))) AAAAmmmmiiiiggggaaaaDDDDOOOOSSSS ((((11115555 OOOOccccttttoooobbbbeeeerrrr 1111999988887777)))) TTTTAAAARRRR((((5555)))) _o_t_h_e_r values are reserved for specification in future revisions of the P1003 standard, and should not be used by any _t_a_r program. The _m_a_g_i_c field indicates that this archive was output in the P1003 archive format. If this field contains TMAGIC, then the _u_n_a_m_e and _g_n_a_m_e 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 _u_i_d and _g_i_d fields. User names longer than TUNMLEN-1 or group names longer than TGNMLEN-1 characters will be truncated. SSSSEEEEEEEE AAAALLLLSSSSOOOO tar(1), ar(5), cpio(5), dump(8), restor(8), restore(8) BBBBUUUUGGGGSSSS Names or link names longer than NAMSIZ-1 characters cannot be archived. This format does not yet address multi-volume archives. NNNNOOOOTTTTEEEESSSS This manual page was adapted by John Gilmore from Draft 6 of the P1003 specification Page 5 (printed 3/8/90)