DUMP(8)

DUMP(8) | System Manager's Manual | DUMP(8)

# NAME

dump, rdump — file system backup

# SYNOPSIS

dump | [-0123456789aceFinStuX] [-B records] [-b blocksize] [-d density] [-f file] [-h level] [-k read-blocksize] [-L label] [-l timeout] [-r cachesize] [-s feet] [-T date] [-x snap-backup] files-to-dump

dump | [-W `|` -w]

(4.3BSD option syntax is implemented for backward compatibility, but not documented here.)

# DESCRIPTION

dump examines files on a file system and determines which files need to be backed up. These files are copied to the given disk, tape or other storage medium for safe keeping (see the -f option below for doing remote backups). A dump that is larger than the output medium is broken into multiple volumes. On most media the size is determined by writing until an end-of-media indication is returned. This can be enforced by using the -a option.

On media that cannot reliably return an end-of-media indication (such as some cartridge tape drives) each volume is of a fixed size; the actual size is determined by the tape size and density and/or block count options below. By default, the same output file name is used for each volume after prompting the operator to change media.

files-to-dump is either a single file system, or a list of files and directories on a single file system to be backed up as a subset of the file system. In the former case, files-to-dump may be the device of a file system, the path to a currently mounted file system, the path to an unmounted file system listed in /etc/fstab, or, if -F is given, a file system image. In the latter case, certain restrictions are placed on the backup: -u is ignored, the only dump level that is supported is -0, and all of the files must reside on the same file system.

Any files with the superuser “log” flag (SF_LOG) set will be skipped. These files are assumed to be wapbl(4) journal files and will not be backed up.

The following options are supported by dump:

-0-9
  Dump levels. A level 0, full backup, guarantees the entire file system is copied (but see also the -h option below). A level number above 0, incremental backup, tells dump to copy all files new or modified since the last dump of a lower level (but see also the -i option below). The default level is 9.
-a
  “auto-size”. Bypass all tape length considerations, and enforce writing until an end-of-media indication is returned. This fits best for most modern tape drives. Use of this option is particularly recommended when appending to an existing tape, or using a tape drive with hardware compression (where you can never be sure about the compression ratio).
-B records
  The number of kilobytes per volume, rounded down to a multiple of the blocksize. This option overrides the calculation of tape size based on length and density.
-b blocksize
  The number of kilobytes per dump record.
-c
  Modify the calculation of the default density and tape size to be more appropriate for cartridge tapes.
-d density
  Set tape density to density. The default is 1600 Bits Per Inch (BPI).
-e
  Eject tape automatically if a tape change is required.
-F
  Indicates that files-to-dump is a file system image.
-f file
  Write the backup to file; file may be a special device file like /dev/rst0 (a tape drive), /dev/rsd1c (a disk drive), an ordinary file, or ‘`-`’ (the standard output). Multiple file names may be given as a single argument separated by commas. Each file will be used for one dump volume in the order listed; if the dump requires more volumes than the number of names given, the last file name will used for all remaining volumes after prompting for media changes. If the name of the file is of the form “host:file”, or “user@host:file”, dump writes to the named file on the remote host using rmt(8). Note that methods more secure than rsh(1) (such as ssh(1)) can be used to invoke rmt(8) on the remote host, via the environment variable RCMD_CMD. See rcmd(3) for more details.
-h level
  Honor the user “nodump” flag (UF_NODUMP) only for dumps at or above the given level. The default honor level is 1, so that incremental backups omit such files but full backups retain them.
-i
  The dump is treated as level 9 but takes into account a previous level 9, if one exists. This makes it possible to perform a “true incremental” dump.
-k read-blocksize
  The size in kilobyte of the read buffers, rounded up to a multiple of the file system block size. Default is 32k.
-L label
  The user-supplied text string label is placed into the dump header, where tools like restore(8) and file(1) can access it. Note that this label is limited to be at most LBLSIZE (currently 16) characters, which must include the terminating ‘`\0`’.
-l timeout
  If a tape change is required, eject the tape and wait for the drive to be ready again. This is to be used with tape changers which automatically load the next tape when the tape is ejected. If after the timeout (in seconds) the drive is not ready dump falls back to the default behavior, and prompts the operator for the next tape.
-n
  Whenever dump requires operator attention, notify all operators in the group “operator” using wall(1).
-r cachesize
  Use that many buffers for read cache operations. A value of zero disables the read cache altogether, higher values improve read performance by reading larger data blocks from the disk and maintaining them in an LRU cache. See the -k option for the size of the buffers. Maximum is 512, the size of the cache is limited to 15% of the avail RAM by default.
-S
  Display an estimate of the backup size and the number of tapes required, and exit without actually performing the dump.
-s feet
  Attempt to calculate the amount of tape needed at a particular density. If this amount is exceeded, dump prompts for a new tape. It is recommended to be a bit conservative on this option. The default tape length is 2300 feet.
-T date
  Use the specified date as the starting time for the dump instead of the time determined from looking in /etc/dumpdates. The format of date is the same as that of ctime(3). This option is useful for automated dump scripts that wish to dump over a specific period of time. The -T option and the -u option are mutually exclusive.
-t
  All informational log messages printed by dump will have the time prepended to them. Also, the completion time interval estimations will have the estimated time at which the dump will complete printed at the end of the line.
-u
  Update the file /etc/dumpdates after a successful dump. The format of /etc/dumpdates is readable by people, consisting of one free format record per line: file system name, increment level and ctime(3) format dump date. There may be only one entry per file system at each level. The file /etc/dumpdates may be edited to change any of the fields, if necessary. If a list of files or subdirectories is being dumped (as opposed to an entire file system), then -u is ignored.
-W
  dump tells the operator what file systems need to be dumped. This information is gleaned from the files /etc/dumpdates and /etc/fstab. The -W option causes dump to print out, for each file system in /etc/dumpdates the most recent dump date and level, and highlights those file systems that should be dumped. If the -W option is set, all other options are ignored, and dump exits immediately.
-w
  Like -W, but prints only those file systems which need to be dumped.
-X
  Similar to -x but uses a file system internal snapshot on the file system to be dumped.
-x snap-backup
  Use a snapshot with snap-backup as backup for this dump. See fss(4) for more details.

If dump honors the “nodump” flag (UF_NODUMP), files with the “nodump” flag will not be backed up. If a directory has the “nodump” flag, this directory and any file or directory under it will not be backed up.

dump requires operator intervention on these conditions: end of tape, end of dump, tape write error, tape open error or disk read error (if there are more than a threshold of 32). In addition to alerting all operators implied by the -n option, dump interacts with the operator on dump's control terminal at times when dump can no longer proceed, or if something is grossly wrong. All questions dump poses must be answered by typing “yes” or “no”, appropriately.

Since making a dump involves a lot of time and effort for full dumps, dump checkpoints itself at the start of each tape volume. If writing that volume fails for some reason, dump will, with operator permission, restart itself from the checkpoint after the old tape has been rewound and removed, and a new tape has been mounted.

dump tells the operator what is going on at periodic intervals, including usually low estimates of the number of blocks to write, the number of tapes it will take, the time to completion, and the time to the tape change. The output is verbose, so that others know that the terminal controlling dump is busy, and will be for some time.

In the event of a catastrophic disk event, the time required to restore all the necessary backup tapes or files to disk can be kept to a minimum by staggering the incremental dumps. An efficient method of staggering incremental dumps to minimize the number of tapes follows:

- Always start with a level 0 backup, for example:

      /sbin/dump -0u -f /dev/nrst1 /usr/src

  This should be done at set intervals, say once a month or once every two months, and on a set of fresh tapes that is saved forever.

- After a level 0, dumps of active file systems are taken on a daily basis, using a modified Tower of Hanoi algorithm, with this sequence of dump levels:

      3 2 5 4 7 6 9 8 9 9 ...

  For the daily dumps, it should be possible to use a fixed number of tapes for each day, used on a weekly basis. Each week, a level 1 dump is taken, and the daily Hanoi sequence repeats beginning with 3. For weekly dumps, another fixed set of tapes per dumped file system is used, also on a cyclical basis.

After several months or so, the daily and weekly tapes should get rotated out of the dump cycle and fresh tapes brought in.

If dump receives a SIGINFO signal (see the “status” argument of stty(1)) whilst a backup is in progress, statistics on the amount completed, current transfer rate, and estimated finished time, will be written to the standard error output.

# ENVIRONMENT

If the following environment variables exist, they are used by dump.

TAPE
  If no -f option was specified, dump will use the device specified via TAPE as the dump device. TAPE may be of the form “tapename”, “host:tapename”, or “user@host:tapename”.
RCMD_CMD
  dump will use RCMD_CMD rather than rsh(1) to invoke rmt(8) on the remote machine.
TIMEFORMAT
  can be used to control the format of the timestamps produced by the -t option. TIMEFORMAT is a string containing embedded formatting commands for strftime(3). The total formatted string is limited to about 80 characters, if this limit is exceeded then “ERROR: TIMEFORMAT too long, reverting to default” will be printed and the time format will revert to the default one. If TIMEFORMAT is not set then the format string defaults to “%T %Z”

# FILES

/dev/nrst0
  default tape unit to use. Taken from _PATH_DEFTAPE in /usr/include/paths.h.
/dev/rst*
  raw SCSI tape interface
/etc/dumpdates
  dump date records
/etc/fstab
  dump table: file systems and frequency
/etc/group
  to find group operator

# DIAGNOSTICS

Many, and verbose.

dump exits with zero status on success. Startup errors are indicated with an exit code of 1; abnormal termination is indicated with an exit code of 3.

# SEE ALSO

chflags(1), rcmd(1), stty(1), wall(1), fts(3), rcmd(3), fss(4), st(4), fstab(5), environ(7), restore(8), rmt(8)

# HISTORY

A dump command appeared in Version 6 AT&T UNIX.

The -i flag was inspired by the -x flag from Sun's Solstice Backup utility.

# BUGS

At least the following caveats can be mentioned.

- Fewer than 32 read errors on the file system are ignored.
- Each reel requires a new process, so parent processes for reels already written just hang around until the entire tape is written.
- dump with the -W or -w options does not report file systems that have never been recorded in /etc/dumpdates, even if listed in /etc/fstab.
- When dumping a list of files or subdirectories, access privileges are required to scan the directory (as this is done via the fts(3) routines rather than directly accessing the file system).
- It would be nice if dump knew about the dump sequence, kept track of the tapes scribbled on, told the operator which tape to mount when, and provided more assistance for the operator running restore(8).
- Snapshot support is experimental. Be sure you have a backup before you use it.

February 19, 2012 | NetBSD 7.0