NAME
dump_lfs,
rdump_lfs —
file system backup
SYNOPSIS
dump_lfs |
[-0123456789aceFnStuX]
[-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_lfs |
[-W |
-w]
(The 4.3BSD option syntax is implemented for
backward compatibility, but is not documented here). |
DESCRIPTION
dump_lfs 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.
The following options are supported by
dump_lfs:
-
-
- -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. 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_lfs 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.
-
-
- -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
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_lfs
falls back to the default behavior, and prompts the operator for the next
tape.
-
-
- -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
’.
-
-
- -n
- Whenever dump_lfs 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
feet
- Attempt to calculate the amount of tape needed at a
particular density. If this amount is exceeded, dump_lfs
prompts for a new tape. It is recommended to be a bit conservative on this
option. The default tape length is 2300 feet.
-
-
- -S
- Display an estimate of the backup size and the number of
tapes required, and exit without actually performing the dump.
-
-
- -t
- All informational log messages printed by
dump_lfs 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.
-
-
- -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 is mutually exclusive from the
-u option.
-
-
- -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.
-
-
- -X
- Prevent the log from wrapping until the dump completes,
guaranteeing a consistent backup. Processes that write to the file system
will continue as usual until the entire log is full, after which they will
block until the dump is complete. This functionality is analogous to what
fss(4) provides for other file
systems. The -x flag is provided for compatibility with
dump(8); it functions exactly
as the -X flag does (its argument is ignored).
-
-
- -W
- dump_lfs 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_lfs 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_lfs exits immediately.
-
-
- -w
- Is like W, but prints only those file systems which need to
be dumped.
If
dump_lfs 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_lfs 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_lfs interacts with the operator on
dump_lfs's control terminal at times when
dump_lfs can no longer proceed, or if something is grossly
wrong. All questions
dump_lfs 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_lfs checkpoints itself at the start of each tape
volume. If writing that volume fails for some reason,
dump_lfs 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_lfs 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_lfs 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:
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_lfs 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_lfs.
-
-
TAPE
- If no -f option was specified, dump_lfs
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_lfs 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_lfs 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),
st(4),
fstab(5),
environ(7),
restore(8),
rmt(8)
HISTORY
A
dump_lfs command appeared in
NetBSD
1.5.
BUGS
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_lfs 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_lfs 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).