OpenBSD-4.6/sbin/dump/dump.8

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.\"     @(#)dump.8	8.1 (Berkeley) 6/16/93
.\"
.Dd $Mdocdate: January 26 2008 $
.Dt DUMP 8
.Os
.Sh NAME
.Nm dump
.Nd filesystem backup
.Sh SYNOPSIS
.Nm dump
.Bk -words
.Op Fl 0123456789acnuWw
.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 s Ar feet
.Op Fl T Ar date
.Ar files-to-dump
.Ek
.Sh DESCRIPTION
.Nm
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
.Fl a
option.
.Pp
.Nm
works across networks,
replacing the functionality of the old
.Nm rdump
program
(though
.Nm
may still be invoked as
.Nm rdump ) .
See the
.Fl f
option for more on writing backups to remote hosts.
.Pp
Files can be marked with the
.Dq nodump
flag using
.Xr chflags 1 ,
settable only by the file's owner or the superuser.
Files with this flag set will only be dumped during full backups.
See also the
.Fl h
option, below.
.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, 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
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
.Fl f
option and
.Xr st 4
for more information.
.Pp
The options are as follows:
.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
.Nm
to
copy all files new or modified since the
last dump of a lower level.
The default level is 0.
.It Fl a
.Dq 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).
.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.
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
.Xr restore 8 .
Therefore
.Nm
will constrain writes to MAXBSIZE.
.It Fl c
Change the defaults for use with a cartridge tape drive, with a density
of 8000 bpi, and a length of 1700 feet.
.It Fl d Ar density
Set tape density to
.Ar density .
The default is 1600BPI.
.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
.Sq -
(the standard output).
See also the
.Ev TAPE
environment variable, below.
.Pp
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
.Dq host:file
or
.Dq user@host:file ,
.Nm
writes to the named file on the remote host using
.Xr rmt 8 .
.It Fl h Ar level
Honor the user
.Dq nodump
flag (see above),
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 n
Whenever
.Nm
requires operator attention,
notify all operators in the group
.Dq operator
by means similar to a
.Xr wall 1 .
.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
flag is mutually exclusive from the
.Fl u
flag.
.It Fl u
Update the file
.Pa /etc/dumpdates
after a successful dump.
The format of
.Pa /etc/dumpdates
is human readable, consisting of one
free format record per line:
filesystem name,
increment level
and
.Xr ctime 3
format dump date.
There may be only one entry per filesystem 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 filesystem), 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
flag 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
flag is set, all other options are ignored, and
.Nm
exits immediately.
.It Fl w
Same as
.Fl W ,
but prints only those filesystems which need to be dumped.
.El
.Pp
.Ar 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
or the device of an unmounted filesystem can be used.
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 filesystem.
.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 is more than a threshold of 32).
In addition to alerting all operators implied by the
.Fl n
flag,
.Nm
interacts with the operator on
.Nm dump 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
.Dq yes
or
.Dq 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
If
.Nm
receives a
.Dv SIGINFO
signal
(see the
.Dq 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
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:
.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 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.
.Pp
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:
.Bd -literal -offset indent
1 2 2 2 2 2 2
.Ed
.Pp
This sequence requires at most eight tapes to restore,
but the size of the individual dumps will be smaller:
.Bd -literal -offset indent
1 2 3 4 5 6 7
.Ed
.Pp
This sequence seeks a compromise between backup and restore effort:
.Bd -literal -offset indent
1 2 2 3 3 4 4
.Ed
.Pp
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.
.It
After several months or so, the daily and weekly tapes should get
rotated out of the dump cycle and fresh tapes brought in.
.El
.Sh ENVIRONMENT
.Bl -tag -width /etc/dumpdates
.It Ev TAPE
The default file to use instead of
.Pa /dev/rst0 .
See also
.Fl f ,
above.
.El
.Sh FILES
.Bl -tag -width /etc/dumpdates -compact
.It Pa /dev/rst0
default tape unit to dump to
.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 stty 1 ,
.Xr fts 3 ,
.Xr rcmd 3 ,
.Xr st 4 ,
.Xr fstab 5 ,
.Xr restore 8 ,
.Xr rmt 8
.Sh HISTORY
A
.Nm
command appeared in
.At v5 .
.Pp
The
.Bx 4.3
option syntax is implemented for backward compatibility but
is not documented here.
.Sh BUGS
Fewer than 32 read errors on the filesystem are ignored.
.Pp
Each reel requires a new process, so parent processes for
reels already written just hang around until the entire tape
is written.
.Pp
.Nm
with the
.Fl W
or
.Fl w
flag does not report filesystems that have never been recorded
in
.Pa /etc/dumpdates ,
even if listed in
.Pa /etc/fstab .
.Pp
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 filesystem).
.Pp
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 .