xbackup(F)                      19 June 1992                      xbackup(F)


 Name

    xbackup - XENIX incremental dump tape format

 Description

    The xbackup and xrestore commands are used to write and read incremental
    dump magnetic tapes.

    The backup tape consists of a header record, some bit mask records, a
    group of records describing file system directories, a group of records
    describing file system files, and some records describing a second bit
    mask.

    The header record and the first record of each description have the for-
    mat described by the structure included by:

       #include <dumprestor.h>

    Fields in the dumprestor structure are described below.

    NTREC is the number of 512 byte blocks in a physical tape record.  MLEN
    is the number of bits in a bit map word.  MSIZ is the number of bit map
    words.

    The TS entries are used in the ctype field to indicate what sort of
    header this is.  The types and their meanings are as follows:

    TSTAPE      Tape volume label.

    TSINODE     A file or directory follows. The cdinode field is a copy of
                 the disk inode and contains bits describing what sort of
                 file this is.

    TSBITS      A bit mask follows. This bit mask has one bit for each inode
                 that was backed up.

    TSADDR      A subblock to a file (TSINODE).  See the description of
                 ccount below.

    TSEND       End of tape record.

    TSCLRI      A bit mask follows. This bit mask contains one bit for all
                 inodes that were empty on the file system when backed up.

    MAGIC        All header blocks have this number in cmagic.

    CHECKSUM     Header blocks checksum to this value.  The fields of the
                 header structure are as follows:

    ctype       The type of the header.

    cdate       The date the backup was taken.

    cddate      The date the file system was backed up.

    cvolume     The current volume number of the backup.

    ctapea      The current block number of this record. This is counting
                 512 byte blocks.

    cinumber    The number of the inode being backed up if this is of type
                 TSINODE.

    cmagic      This contains the value MAGIC above, truncated as needed.

    cchecksum   This contains whatever value is needed to make the block sum
                 to CHECKSUM.

    cdinode     This is a copy of the inode as it appears on the file sys-
                 tem.

    ccount      The following count of characters describes the file.  A
                 character is zero if the block associated with that charac-
                 ter was not present on the file system; otherwise, the char-
                 acter is nonzero.  If the block was not present on the file
                 system no block was backed up and it is replaced as a hole
                 in the file.  If there is not sufficient space in this block
                 to describe all of the blocks in a file, TSADDR blocks will
                 be scattered through the file, each one picking up where the
                 last left off.

    caddr       This is the array of characters that is used as described
                 above.

    Each volume except the last ends with a tapemark (read as an end of
    file). The last volume ends with a TSEND block and then the tapemark.

    The structure idates describes an entry of the file where backup history
    is kept.

 See also

    xbackup(ADM), xrestore(ADM), filesys(F)

 Value added

    xbackup is an extension of AT&T System V provided by The Santa Cruz
    Operation, Inc.