⟦a9848decf⟧

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.TH MULTIVOL 8 local
.SH NAME
multivol \- handle multivolume files
.SH SYNOPSIS
.B multivol
.B \-o
.RB [ \-vtw ]
.RB [ \-b
.IR blocksize ]
.RB [ \-n
.IR count ]
.RB [ \-l
.IR label ]
.RI [ device ]
.PP
.B multivol
.B \-i
.RB [ \-vtw ]
.RB [ \-b
.IR blocksize ]
.RB [ \-n
.IR count ]
.RB [ \-l
.IR label ]
.RI [ device ]
.PP
.B multivol
.B \-t
.RI [ device ]
.SH DESCRIPTION
.I Multivol
allows for the convenient use of multiple volume files such as when
backing up output from 
.I cpio/tar
over several floppy disks.
.PP
Option
.B \-o
reads the standard input file, breaking it into volumes on the output device.
Option
.BR \-i
reads volumes from the device, concatenates them
and writes the result to standard output.
.PP
The device to use is given by the
.I device
argument, or
.I /dev/multivol
if none is specified.
Normally this will be a character special file corresponding to a raw
disk or tape unit.
It does not have to be a random access device:
.I multivol
only accesses it sequentially.
However,
.I multivol
may close and re-open a volume in order to rewind devices such as magnetic tape.
.PP
The
.B \-b
.I blocksize
argument specifies the physical block size to be used.
This number may end with
.B k
or
.B b
to specify multiplication by
1024 or 512 respectively.
With a floppy disk it can usefully be made the size of one
track.
The default physical block size is 512 bytes.
If the device or its driver does not allow successful writing all the way to the
end of a physical volume, such as with magnetic tape, the
.B \-n
.I count
options should be used to specify the maximum number of physical blocks
to be written on one volume.
.PP
The
.B \-l
.I label
option allows the user to supply a short string to be written onto
the volume for identification.
.PP
Before reading or writing a new volume,
.I multivol
prompts on the controlling terminal for the user to insert the appropriate
volume into the physical device and waits for a new-line to be typed.
With
.BR \-i ,
if the volume inserted is not a
.I multivol
volume,
is not the next volume in sequence,
or does not have the same date stamp as the previous volume,
.I multivol
verifies that you really want to read it.
.PP
.I Multivol
writes an \s-2ASCII\s0 header on each volume, 
and checksum info in each block
hence the actual amount of data stored on each volume will be slightly less
than its physical size.
The
.B \-t
option prints some of this header information on standard error.
It includes:
.IP \(bu
the date that the volume was written
.IP \(bu
the sequence number of the volume
.IP \(bu
any
.I label
string supplied at the time the volume was written
.LP
If you specify
.B \-w
with
.B \-i
or
.B \-o
.I multivol
assumes the
.B \-t
option also and
asks you to verify that each volume really is the required one.
.PP
The
.B \-v
option tells
.I multivol
to write various other verbose information on standard error
such as an indication of how many blocks it has read or written.
.SH EXAMPLES
Tell me what you know about this volume:
.br
	multivol \-t
.LP
Backup a directory to the default device:
.br
	tar cf \- mydir | multivol \-o
.sp
and retrieve it again:
.br
	cd mydir
.br
	multivol \-i | tar xf \-
.LP
Backup to tape all files changed since last time:
.br
	touch /etc/multivoldate1
.br
	find / \-newer /etc/multivoldate2 \-print | cpio \-ov |
.br
		multivol \-o \-l WEEKLY \-b 20k \-n 1000 /dev/rmt0
.br
	mv /etc/multivoldate1 /etc/multivoldate2
.sp
Retrieve a file from that backup:
.br
	cd /
.br
	multivol \-i /dev/rmt0 | cpio \-idmv usr/myname/myfile
.SH FILES
.ta \w'/dev/multivol     'u
.nf
/dev/tty	where prompts are written and responses read
.br
/dev/multivol	the default device
.SH SEE ALSO
tar(1), cpio(1), dd(1), dump(8), ``your device''(4)
.SH DIAGNOSTICS
.PP
A message is written on standard error and
.I multivol
terminates in the event of
.IP \(bu
incorrect usage
.IP \(bu
not being able to open the device
.IP \(bu
not being able to open /dev/tty
.IP \(bu
a device I/O error 
.SH BUGS
In the event of an I/O error you may have to start again with the first volume
depending on the nature of the file and the program which produced it.  In
many cases it simply means the end of the volume has been reached, and no more
can be read/written.  If a block limit has been set
.I multivol
will indicate this condition.
.PP
When reading or writting,
.I multivol
attempts to read the volumes header to display what is being written over,
or to determine the block size recorded in the header.
Some raw devices will return an I/O error
when the volume has not been written before, or has been previously written
with a different block size.
Hence the volume header cannot be read until the original
block size is also specified.
The first time a volume is written,
.I multivol
may signal an I/O error as it attempts to read the header, but will proceed 
to allow the volume to be written.
.PP
Volume labels may not contain white space and are limited to 14 characters.
.PP
Some tape device drivers cannot handle a read/write request while the tape
is rewinding, for such drivers the
.B \-w
switch is recommended in place of just
.B \-t
\.
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