119 lines
4.1 KiB
Groff
119 lines
4.1 KiB
Groff
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VOL(1) Minix Programmer's Manual VOL(1)
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NAME
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vol - split input on or combine output from several volumes
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SYNOPSIS
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vol [-rw1] [-b blocksize] [-m multiple] [size] device
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DESCRIPTION
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Vol either reads a large input stream from standard input and distributes
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it over several volumes or combines volumes and sends them to standard
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output. The size of the volumes is determined automatically if the
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device supports this, but may be specified before the argument naming the
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device if automated detection is not possible or if only part of the
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physical volume is used. The direction of the data is automatically
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determined by checking whether the input or output of vol is a file or
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pipe. Use the -r or -w flag if you want to specify the direction
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explicitly, in shell scripts for instance.
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Vol waits for each new volume to be inserted, typing return makes it
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continue. If no size is explicitely given then the size of the device is
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determined each time before it is read or written, so it is possible to
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mix floppies of different sizes. If the size cannot be determined
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(probably a tape) then the device is assumed to be infinitely big. Vol
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can be used both for block or character devices. It will buffer the data
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and use a block size appropriate for fixed or variable block sized tapes.
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Vol reads or writes 8192 bytes to block devices, usually floppies.
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Character devices are read or written using a multiple of 512 bytes.
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This multiple has an upper limit of 32767 bytes (16-bit machine), 64 kb
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(32-bit), or even 1 Mb (32-bit VM). The last partial write to a
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character device is padded with zeros to the block size. If a character
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device is a tape device that responds to the mtio(4) status call then the
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reported tape block size will be used as the smallest unit. If the tape
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is a variable block length device then it is read or written like a block
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device, 8192 bytes at the time, with a minimum unit of one byte.
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All sizes may be suffixed by the letters M, k, b or w to multiply the
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number by mega, kilo, block (512), or word (2). The volume size by
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default in kilobytes if there is no suffix.
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OPTIONS
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-rw Explicitly specify reading or writing. Almost mandatory in scripts.
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-1 Just one volume, start immediately.
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-b blocksize
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Specify the device block size.
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1
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VOL(1) Minix Programmer's Manual VOL(1)
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-m multiple
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Specify the maximum read or write size of multiple blocks. The -b
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and -m options allow one to modify the block size assumptions that
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are made above. These assumptions are -b 1 -m 8192 for block
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devices or variable length tapes, and -b 512 -m 65536 for character
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devices (32 bit machine.) These options will not override the tape
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block size found out with an mtio(4) call. The multiple may be
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larger then the default if vol can allocate the memory required.
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EXAMPLES
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To back up a tree to floppies as a compressed tarfile:
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tar cf - . | compress | vol /dev/fd0
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To restore a tree from 720 kb images from possibly bigger floppies:
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vol 720 /dev/fd0 | uncompress | tar xfp -
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Read or write a device with 1024 byte blocks:
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vol -b 1k /dev/rsd15
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Read or write a variable block length tape using blocking factor 20 as
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used by default by many tar(1) commands:
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vol -m 20b /dev/rst5
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Note that -m was used in the last example. It sets the size to use to
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read or write, -b sets the basic block size that may be written in
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multiples.
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SEE ALSO
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dd(1), tar(1), mt(1), mtio(4).
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