— filesystem backup
dump examines files on a filesystem 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. 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
dump works across networks, replacing the
functionality of the old
rdump program (though
dump may still be invoked as
rdump). See the
for more on writing backups to remote hosts.
Files can be marked with the “nodump” flag using
chflags(1), settable only by the file's owner or the superuser. Files
with this flag set will only be dumped during full backups. When set on a
directory, “nodump” effectively deselects the whole subtree
from being dumped, though it will still be scanned. See also the
-h option, below.
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, 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.
Rewinding or ejecting tape features after a close operation on a
tape device depend on the name of the tape unit device used. See the
-f option and
for more information.
The options are as follows:
- Dump levels. A level 0, full backup, guarantees the entire file system is
copied (but see also the
-hoption below). A level number above 0, incremental backup, tells
dumpto copy all files new or modified since the last dump of a lower level. The default level is 0.
- “auto-size”. Bypass all tape length considerations, and enforce writing until an end-of-media indication is returned. This option is recommended 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).
- 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.
- The number of kilobytes per dump record. Since the I/O system slices all
requests into chunks of MAXBSIZE (typically 64KB), it is not possible to
use a larger blocksize without having problems later with
dumpwill constrain writes to MAXBSIZE.
- Change the defaults for use with a cartridge tape drive, with a density of 8000 bpi, and a length of 1700 feet.
- Set tape density to density. The default is 1600BPI.
- 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). See also the
TAPEenvironment variable, below.
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 be 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”,
dumpwrites to the named file on the remote host using rmt(8).
- Honor the user “nodump” flag (see above), 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.
dumprequires operator attention, notify all operators in the group “operator” by means similar to a wall(1).
- Display an estimate of the backup size and the number of tapes required, and exit without actually performing the dump.
- Attempt to calculate the amount of tape needed at a particular density. If
this amount is exceeded,
dumpprompts for a new tape. It is recommended to be a bit conservative on this option. The default tape length is 2300 feet.
- 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
-Tflag is mutually exclusive from the
- Update the file /etc/dumpdates after a successful
dump. The format of /etc/dumpdates is human
readable, consisting of one free format record per line: filesystem name
disklabel(8) UID when possible), increment level and
ctime(3) format dump date. There may be only one entry per
filesystem 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
dumptells the operator what file systems need to be dumped. This information is gleaned from the files /etc/dumpdates and /etc/fstab. The
dumpto 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
-Wflag is set, all other options are ignored, and
- Same as
-W, but prints only those filesystems which need to be dumped.
files-to-dump is either a mountpoint of a
filesystem or a list of files and directories on a single filesystem to be
backed up as a subset of the filesystem. In the former case, either the path
to a mounted filesystem, the device of an unmounted filesystem or the
disklabel(8) UID can be used. In the latter case, certain
restrictions are placed on the backup:
ignored, the only dump level that is supported is
-0, and all of the files must reside on the same
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 is more than a threshold
of 32). In addition to alerting all operators implied by the
dump interacts with
the operator on
dump's control terminal at times
dump can no longer proceed, or if something is
grossly wrong. All questions
must be answered by
typing “yes” or “no”, appropriately.
Since making a dump involves a lot of time and effort for full
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.
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.
In the event of a catastrophic disk event, the time required to restore all the necessary backup tapes or files to disk is dependent on the levels of the dumps taken. A few methods of staggering incremental dumps to either minimize backup effort or restore effort follow:
- 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 the level 0 dump, backups of active file systems are taken on each
day in a cycle of a week. Once a week, a level 1 dump is taken. The other
days of the week a higher level dump is done.
The following cycle needs at most three tapes to restore to a given point in time, but the dumps at the end of the weekly cycle will require more time and space:
1 2 2 2 2 2 2
This sequence requires at most eight tapes to restore, but the size of the individual dumps will be smaller:
1 2 3 4 5 6 7
This sequence seeks a compromise between backup and restore effort:
1 2 2 3 3 4 4
The weekly level 1 dumps should be done on a set of tapes that is used cyclically. For the daily dumps a tape per day of the week can be used.
- After several months or so, the daily and weekly tapes should get rotated out of the dump cycle and fresh tapes brought in.
- The default file to use instead of /dev/rst0. See
- default tape unit to dump to
- raw SCSI tape interface
- dump date records
- dump table: file systems and frequency
- to find group operator
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.
chflags(1), stty(1), fts(3), rcmd(3), st(4), fstab(5), restore(8), rmt(8)
dump command appeared in
Version 5 AT&T UNIX.
The 4.3BSD option syntax is implemented for backward compatibility but is not documented here.
Fewer than 32 read errors on the filesystem 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 flag does not report filesystems 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 filesystem).
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