NetBSD/sbin/dump/dump.8

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.\"     @(#)dump.8	8.3 (Berkeley) 5/1/95
.\"
.Dd July 15, 2018
.Dt DUMP 8
.Os
.Sh NAME
.Nm dump ,
.Nm rdump
.Nd file system backup
.Sh SYNOPSIS
.Nm
.Op Fl 0123456789aceFinStuX
.Op Fl B Ar records
.Op Fl b Ar blocksize
.Op Fl d Ar density
.Op Fl f Ar file
.Op Fl h Ar level
.Op Fl k Ar read-blocksize
.Op Fl L Ar label
.Op Fl l Ar timeout
.Op Fl r Ar cachesize
.Op Fl s Ar feet
.Op Fl T Ar date
.Op Fl x Ar snap-backup
.Ar files-to-dump
.Nm
.Op Fl W Li \&| Fl w
.Pp
.in -\n[indent-synopsis]u
.Pf ( Bx 4.3
option syntax is implemented for backward compatibility, but
not documented here.)
.Sh DESCRIPTION
.Nm
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
.Fl 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
.Fl a
option.
.Pp
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.
.Pp
.Ar 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,
.Ar 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
.Pa /etc/fstab ,
or, if
.Fl F
is given, a file system image.
In the latter case, certain restrictions are placed on the backup:
.Fl u
is ignored, the only dump level that is supported is
.Fl 0 ,
and all of the files must reside on the same file system.
.Pp
Any files with the superuser
.Qq log
flag
.Pq Dv SF_LOG
set will be skipped.
These files are assumed to be
.Xr wapbl 4
journal files and will not be backed up.
.Pp
The following options are supported by
.Nm :
.Bl -tag -width Ds
.It Fl 0\-9
Dump levels.
A level 0, full backup, guarantees the entire file system is copied
(but see also the
.Fl 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
.Fl i
option below).
The default level is 9.
.It Fl a
.Dq 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).
.It Fl B Ar 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.
.It Fl b Ar blocksize
The number of kilobytes per dump record.
.It Fl c
Modify the calculation of the default density and tape size to be more
appropriate for cartridge tapes.
.It Fl d Ar density
Set tape density to
.Ar density .
The default is 1600 Bits Per Inch (BPI).
.It Fl e
Eject tape automatically if a tape change is required.
.It Fl F
Indicates that
.Ar files-to-dump
is a file system image.
.It Fl f Ar file
Write the backup to
.Ar file ;
.Ar file
may be a special device file like
.Pa /dev/rst0
(a tape drive),
.Pa /dev/rsd1c
(a disk drive),
an ordinary file, or
.Ql Fl
(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 be used for all remaining volumes after prompting
for media changes.
If the name of the file is of the form
.Qq host:file ,
or
.Qq user@host:file ,
.Nm
writes to the named file on the remote host using
.Xr rmt 8 .
Note that methods more secure than
.Xr rsh 1
.Pq such as Xr ssh 1
can be used to invoke
.Xr rmt 8
on the remote host, via the environment variable
.Ev RCMD_CMD .
See
.Xr rcmd 3
for more details.
.It Fl h Ar level
Honor the user
.Qq nodump
flag
.Pq Dv UF_NODUMP
only for dumps at or above the given
.Ar level .
The default honor level is 1,
so that incremental backups omit such files
but full backups retain them.
.It Fl 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
.Dq true incremental
dump.
.It Fl k Ar read-blocksize
The size in kilobytes of the read buffers, rounded up to a multiple of the
file system block size.
Default is the value of the
.Xr sysctl 7
kern.maxphys.
.It Fl L Ar label
The user-supplied text string
.Ar label
is placed into the dump header, where tools like
.Xr restore 8
and
.Xr file 1
can access it.
Note that this label is limited to be at most LBLSIZE
(currently 16) characters, which must include the terminating
.Ql \e0 .
.It Fl l Ar 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
.Nm
falls back to the default behavior,
and prompts the operator for the next tape.
.It Fl n
Whenever
.Nm
requires operator attention,
notify all operators in the group
.Qq operator
using
.Xr wall 1 .
.It Fl r Ar 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
.Fl 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.
.It Fl S
Display an estimate of the backup size and the number of tapes
required, and exit without actually performing the dump.
.It Fl s Ar feet
Attempt to calculate the amount of tape needed
at a particular density.
If this amount is exceeded,
.Nm
prompts for a new tape.
It is recommended to be a bit conservative on this option.
The default tape length is 2300 feet.
.It Fl T Ar date
Use the specified date as the starting time for the dump
instead of the time determined from looking in
.Pa /etc/dumpdates .
The format of
.Ar date
is the same as that of
.Xr ctime 3 .
This option is useful for automated dump scripts that wish to
dump over a specific period of time.
The
.Fl T
option and the
.Fl u
option are mutually exclusive.
.It Fl t
All informational log messages printed by
.Nm
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.
.It Fl u
Update the file
.Pa /etc/dumpdates
after a successful dump.
The format of
.Pa /etc/dumpdates
is readable by people, consisting of one
free format record per line:
file system name,
increment level
and
.Xr ctime 3
format dump date.
There may be only one entry per file system at each level.
The file
.Pa /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
.Fl u
is ignored.
.It Fl W
.Nm
tells the operator what file systems need to be dumped.
This information is gleaned from the files
.Pa /etc/dumpdates
and
.Pa /etc/fstab .
The
.Fl W
option causes
.Nm
to print out, for each file system in
.Pa /etc/dumpdates
the most recent dump date and level,
and highlights those file systems that should be dumped.
If the
.Fl W
option is set, all other options are ignored, and
.Nm
exits immediately.
.It Fl w
Like
.Fl W ,
but prints only those file systems which need to be dumped.
.It Fl X
Similar to
.Fl x
but uses a file system internal snapshot on the file system to be dumped.
.It Fl x Ar snap-backup
Use a snapshot with
.Ar snap-backup
as backup for this dump.
See
.Xr fss 4
for more details.
.El
.Pp
If
.Nm
honors the
.Qq nodump
flag
.Pq Dv UF_NODUMP ,
files with the
.Qq nodump
flag will not be backed up.
If a directory has the
.Qq nodump
flag, this directory and any file or directory under it will not be backed up.
.Pp
.Nm
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
.Fl n
option,
.Nm
interacts with the operator on
.Nm Ns 's
control terminal at times when
.Nm
can no longer proceed,
or if something is grossly wrong.
All questions
.Nm
poses
.Em must
be answered by typing
.Qq yes
or
.Qq no ,
appropriately.
.Pp
Since making a dump involves a lot of time and effort for full dumps,
.Nm
checkpoints itself at the start of each tape volume.
If writing that volume fails for some reason,
.Nm
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.
.Pp
.Nm
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
.Nm
is busy,
and will be for some time.
.Pp
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:
.Bl -bullet -offset indent
.It
Always start with a level 0 backup, for example:
.Bd -literal -offset indent
/sbin/dump -0u -f /dev/nrst1 /usr/src
.Ed
.Pp
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.
.It
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:
.Bd -literal -offset indent
3 2 5 4 7 6 9 8 9 9 ...
.Ed
.Pp
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.
.El
.Pp
After several months or so, the daily and weekly tapes should get
rotated out of the dump cycle and fresh tapes brought in.
.Pp
If
.Nm
receives a
.Dv SIGINFO
signal
(see the
.Qq status
argument of
.Xr 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.
.Pp
The historic alternate name
.Nm rdump
was once required when dumping to a remote host.
This functionality is now built into
.Nm
itself.
.Sh ENVIRONMENT
If the following environment variables exist, they are used by
.Nm .
.Bl -tag -width Fl
.It Ev TAPE
If no -f option was specified,
.Nm
will use the device specified via
.Ev TAPE
as the dump device.
.Ev TAPE
may be of the form
.Qq tapename ,
.Qq host:tapename ,
or
.Qq user@host:tapename .
.It Ev RCMD_CMD
.Nm
will use
.Ev RCMD_CMD
rather than
.Xr rsh 1
to invoke
.Xr rmt 8
on the remote machine.
.It Ev TIMEFORMAT
can be used to control the format of the timestamps produced by the
.Fl t
option.
.Ev TIMEFORMAT
is a string containing embedded formatting commands for
.Xr strftime 3 .
The total formatted string is limited to about 80 characters, if this
limit is exceeded then
.Qo
ERROR: TIMEFORMAT too long, reverting to default
.Qc
will be printed and the time format will revert to the default one.
If
.Ev TIMEFORMAT
is not set then the format string defaults to
.Qo
%T %Z
.Qc
.El
.Sh FILES
.Bl -tag -width /etc/dumpdates -compact
.It Pa /dev/nrst0
default tape unit to use.
Taken from
.Dv _PATH_DEFTAPE
in
.Pa /usr/include/paths.h .
.It Pa /dev/rst*
raw SCSI tape interface
.It Pa /etc/dumpdates
dump date records
.It Pa /etc/fstab
dump table: file systems and frequency
.It Pa /etc/group
to find group
.Em operator
.El
.Sh DIAGNOSTICS
Many, and verbose.
.Pp
.Nm
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.
.Sh SEE ALSO
.Xr chflags 1 ,
.Xr rcmd 1 ,
.Xr stty 1 ,
.Xr wall 1 ,
.Xr fts 3 ,
.Xr rcmd 3 ,
.Xr fss 4 ,
.Xr st 4 ,
.Xr fstab 5 ,
.Xr environ 7 ,
.Xr restore 8 ,
.Xr rmt 8
.Sh HISTORY
A
.Nm
command appeared in
.At v4 .
.Pp
The
.Fl i
flag was inspired by the
.Fl x
flag from Sun's Solstice Backup utility.
.Sh BUGS
At least the following caveats can be mentioned.
.Bl -bullet
.It
Fewer than 32 read errors on the file system are ignored.
.It
Each reel requires a new process, so parent processes for
reels already written just hang around until the entire tape
is written.
.It
.Nm
with the
.Fl W
or
.Fl w
options does not report file systems that have never been recorded
in
.Pa /etc/dumpdates ,
even if listed in
.Pa /etc/fstab .
.It
When dumping a list of files or subdirectories, access privileges are
required to scan the directory (as this is done via the
.Xr fts 3
routines rather than directly accessing the file system).
.It
It would be nice if
.Nm
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
.Xr restore 8 .
.It
Snapshot support is
.Em experimental .
Be sure you have a backup before you use it.
.El