*** UNIX MANUAL PAGE BROWSER ***

BACKUP(5) File Formats Manual BACKUP(5) NAME backup - incremental backup files DESCRIPTION The backup system consists of a number of client machines, and a `backup machine', which has a database and a collection of backup copies of files. On clients files concerned with backup live in a di- rectory, normally defined in the shell script The file needed on both client and backup machine, has up to three lines, namely the backup ma- chine name, the default backup device, and the directory, hereafter called $FM, where the rest of the backup software lives on the backup machine. Client systems normally have just the first line. The rest of this description applies to the backup machine. The databases live in $FM/db and are maintained in cbt(3) form. The main database, called stores two mappings. The first maps filename- time pairs to backup copy names, thus: /n/bowell/usr/jim/goo//519487622 v/v22/17 The number after is the inode change date, expressed in seconds since the epoch; see stat(2). If the backup copy is still on magnetic disk, it will be called $FM/v/v22/17; otherwise it will be v22/17 on some op- tical disk. (The mapping of backup copy name to optical disk name is kept in $FM/adm/volidmap.) The second mapping maps filenames to the time of their most recently backed-up version: /n/bowell/usr/jim/goo 520514116 The second database, dir, maps directoryname-time pairs to the contents of that directory. This allows quick recovery of file trees. The third database, fs, maps filename-time pairs to (essentially) in- odes. This allows efficient implementation of backup mount; see backup(1). The program $FM/bin/dbupdate manages these databases. The dir and fs databases are optional; they will be updated only if they already ex- ist. The program also assigns the backup copy names into a flat direc- tory structure. A new directory is used when the total size of the files in the current directory would exceed 20000K bytes, rounding each file size up to a multiple of 4K. The backup copy of a file consists of a header that gives the original inode, pathname and owner (as a string), followed by the contents of the file. Directories are stored as a sequence of entry names. To prevent multiple writers into a database, a lockfile is used. The content of this file is the process id of the process accessing the database. Locks are removed by executed by rc(8) when the system boots. The backup system supports multiple filemap databases (this allows the current database to be kept small). The list of database names is kept in one per line in order of increasing priority. The last name is as- sumed to be the active database; all the others are read-only. Programs such as sweep and dbupdate leave droppings in the log file Statistics of the numbers of files and bytes saved for users of a given system are kept in Each file consists of a sequence of records with a machine-independent structure; generally, one record per user per day. The records are maintained by which processes the file that is main- tained by dbupdate. To allow quick searching for filenames with full regular expressions, a simple sorted list of all saved filenames is often kept, normally in The device (and system) used for recovering files can be specified in many ways. In order of decreasing priority: a -f option in backup re- cover or backup fetch (see backup(1)), a default device on the client system (in line 2 of the default device on the backup system. FILES SEE ALSO backup(1), worm(8), backup(8), cbt(1), stat(2) A. Hume, `The File Motel: an Owner's Manual', this manual, Volume 2 BACKUP(5)