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DUMP(8) |
FreeBSD System Manager's Manual |
DUMP(8) |
dump , rdump —
file system backup
dump |
[-0123456789acLnrRSu ]
[-B records]
[-b blocksize]
[-C cachesize]
[-D dumpdates]
[-d density]
[-f file |
-P pipecommand]
[-h level]
[-s feet]
[-T date]
filesystem |
The dump utility 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
-B options. By default, the same output file name is
used for each volume after prompting the operator to change media.
The file system to be dumped is specified by the argument
filesystem as either its device-special file or its
mount point (if that is in a standard entry in
/etc/fstab).
dump may also be invoked as
rdump . The 4.3BSD option
syntax is implemented for backward compatibility, but is not documented
here.
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 any lower level. The default level is
0.
-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 output volume, except that if it is not an
integer multiple of the output block size, the command uses the next
smaller such multiple. This option overrides the calculation of tape size
based on length and density.
-b
blocksize
- The number of kilobytes per output block. The default block size is
10.
-C
cachesize
- Specify the cache size in megabytes. This will greatly improve performance
at the cost of
dump possibly not noticing changes
in the file system between passes unless a snapshot is being used. The
potential for performance improvement indicates that use of this option
together with snapshots is the recommended course of action. Beware that
dump forks, and the actual memory use may be
larger than the specified cache size. The recommended cache size is
between 8 and 32 (megabytes).
-c
- Change the defaults for use with a cartridge tape drive, with a density of
8000 bpi, and a length of 1700 feet.
-D
dumpdates
- Specify an alternate path to the dumpdates file.
The default is /etc/dumpdates.
-d
density
- Set tape density to density. The default is
1600BPI.
-f
file
- Write the backup to file; file
may be a special device file like /dev/sa0 (a tape
drive), /dev/fd1 (a floppy 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).
The default path name of the remote
rmt(8)
program is /etc/rmt; this can be overridden by the
environment variable RMT .
-P
pipecommand
- Use
popen(3)
to execute the
sh(1)
script string defined by pipecommand for the output
device of each volume. This child pipeline's
stdin
(/dev/fd/0) is redirected from the
dump output stream, and the environment variable
DUMP_VOLUME is set to the current volume number
being written. After every volume, the writer side of the pipe is closed
and pipecommand is executed again. Subject to the
media size specified by -B , each volume is written
in this manner as if the output were a tape drive.
-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.
-L
- This option is to notify
dump that it is dumping a
live file system. To obtain a consistent dump image,
dump takes a snapshot of the file system in the
.snap directory in the root of the file system
being dumped and then does a dump of the snapshot. The snapshot is
unlinked as soon as the dump starts, and is thus removed when the dump is
complete. This option is ignored for unmounted or read-only file systems.
If the .snap directory does not exist in the root
of the file system being dumped, a warning will be issued and the
dump will revert to the standard behavior. This
problem can be corrected by creating a .snap
directory in the root of the file system to be dumped; its owner should be
“root ”, its group should be
“operator ”, and its mode should be
“0770 ”.
-n
- Whenever
dump requires operator attention, notify
all operators in the group “operator” by means similar to a
wall(1).
-r
- Be rsync-friendly. Normally dump stores the date of the current and prior
dump in numerous places throughout the dump. These scattered changes
significantly slow down rsync or another incremental file transfer program
when they are used to update a remote copy of a level 0 dump, since the
date changes for each dump. This option sets both dates to the epoch,
permitting rsync to be much more efficient when transferring a dump file.
The
-r option can be used only to create level 0
dumps. A dump using the -r option cannot be used
as the basis for a later incremental dump.
-R
- Be even more rsync-friendly. This option disables the storage of the
actual inode access time (storing it instead as the inode's modified
time). This option permits rsync to be even more efficient when
transferring dumps generated from filesystems with numerous files which
are not changing other than their access times. The
-R option also sets -r .
The -R option can be used only to create level 0
dumps. A dump using the -R option cannot be used
as the basis for a later incremental dump.
-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 the dumpdates
file. 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 is mutually
exclusive from the -u option.
-u
- Update the dumpdates file after a successful dump.
The format of the dumpdates file 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 dumpdates file may be edited to change
any of the fields, if necessary. The default path for the
dumpdates file is
/etc/dumpdates, but the
-D
option may be used to change it.
-W
- Tell the operator what file systems need to be dumped. This information is
gleaned from the files dumpdates and
/etc/fstab. The
-W option
causes dump to print out, for each file system in
the dumpdates file 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
- Is like
-W , but prints only those file systems
which need to be dumped.
Directories and regular files which have their
“nodump” flag (UF_NODUMP ) set will be
omitted along with everything under such directories, subject to the
-h option.
The dump utility 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 key, 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.
The dump utility tells the operator what
is going on at periodic intervals (every 5 minutes, or promptly after
receiving SIGINFO ), 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/nsa0 /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 (file systems with files
that change, depending on your partition layout some file systems may
contain only data that does not change) are taken on a daily basis, using
a modified Tower of Hanoi algorithm, with this sequence of dump levels:
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.
TAPE
- The file or device to dump to if the
-f option is not used.
RMT
- Pathname of the remote
rmt(8)
program.
RSH
- Pathname of a remote shell program, if not
rsh(1).
- /dev/sa0
- default tape unit to dump to
- /etc/dumpdates
- dump date records (this can be changed; see the
-D
option)
- /etc/fstab
- dump table: file systems and frequency
- /etc/group
- to find group operator
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.
Dumps the /u file system to DVDs using
growisofs . Uses a 16MB cache, creates a snapshot of
the dump, and records the dumpdates file.
/sbin/dump -0u -L -C16 -B4589840 -P 'growisofs -Z /dev/cd0=/dev/fd/0' /u
A dump utility appeared in
Version 4 AT&T UNIX.
Fewer than 32 read errors on the file system are ignored, though all errors will
generate a warning message. This is a bit of a compromise. In practice, it is
possible to generate read errors when doing dumps on mounted partitions if the
file system is being modified while the dump is
running. Since dumps are often done in an unattended fashion using
cron(8)
jobs asking for Operator intervention would result in the
dump dying. However, there is nothing wrong with a
dump tape written when this sort of read error occurs, and there is no reason
to terminate the dump .
Each reel requires a new process, so parent processes for reels
already written just hang around until the entire tape is written.
The dump utility with the
-W or -w options does not
report file systems that have never been recorded in the
dumpdates file, even if listed in
/etc/fstab.
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).
The dump utility cannot do remote backups
without being run as root, due to its security history. This will be fixed
in a later version of FreeBSD. Presently, it works
if you set it setuid (like it used to be), but this might constitute a
security risk.
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