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ht(4) [v7 man page]

HT(4)							     Kernel Interfaces Manual							     HT(4)

ht - RH-11/TU-16 magtape interface DESCRIPTION
The files mt0, mt1, ... refer to the DEC RH/TM/TU16 magtape. When opened for reading or writing, the tape is not rewound. When closed, it is rewound (unless the 0200 bit is on, see below). If the tape was open for writing, a double end-of-file is written. If the tape is not to be rewound the tape is backspaced to just between the two tapemarks. A standard tape consists of a series of 512 byte records terminated by a double end-of-file. To the extent possible, the system makes it possible, if inefficient, to treat the tape like any other file. Seeks have their usual meaning and it is possible to read or write a byte at a time. Writing in very small units is inadvisable, however, because it tends to create monstrous record gaps. The last octal digit of the minor device number selects the drive. The middle digit selects a controller. The initial digit is even to select 800 BPI, odd to select 1600 BPI. If the 0200 bit is on (initial digit 2 or 3), the tape is not rewound on close. Note that the minor device number has no necessary connection with the file name, and in fact tp(1) turns the short name x into `/dev/mtx'. The mt files discussed above are useful when it is desired to access the tape in a way compatible with ordinary files. When foreign tapes are to be dealt with, and especially when long records are to be read or written, the `raw' interface is appropriate. The associated files may be named rmt0, ..., rmt7, but the same minor-device considerations as for the regular files still apply. Each read or write call reads or writes the next record on the tape. In the write case the record has the same length as the buffer given. During a read, the record size is passed back as the number of bytes read, provided it is no greater than the buffer size; if the record is long, an error is indicated. In raw tape I/O, the buffer must begin on a word boundary and the count must be even. Seeks are ignored. A zero count is returned when a tape mark is read; another read will fetch the first record of the next tape file. FILES
/dev/mt?, /dev/rmt? SEE ALSO
tp(1) BUGS
The magtape system is supposed to be able to take 64 drives. Such addressing has never been tried. Taking a drive off line, or running off the end of tape, while writing have been known to hang the system. If any non-data error is encountered, it refuses to do anything more until closed. In raw I/O, there should be a way to perform forward and backward record and file spacing and to write an EOF mark explicitly. HT(4)

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MT(1)							      General Commands Manual							     MT(1)

mt - magnetic tape control SYNOPSIS
mt [-f device] [count] DESCRIPTION
Mt is a user interface to the magnetic tape commands described in mtio(4). It allows one to space a tape forwards or backwards, write end of file markers, etc. With the -f option a tape device can be named, otherwise the environment variable TAPE is used if set, otherwise the default device /dev/nrst4 is assumed. Standard input is used if the tape name is a dash (-). The count argument is used to tell how many blocks or files to space or how many file markers to write. It may be a C-style decimal, octal or hexadecimal constant, by default "1". Command is the action to perform, it may be one of the following, or any unambiguous prefix (like st for status): eof, weof Write count end-of-file markers. fsf Forward space count file markers. fsr Forward space count records. (The size of a record depends on the tape, and may even be variable, depending on the size of the writes.) bsf Backwards space count files. The count may be zero to backspace to the start of the current file. (A tape device need not support backwards movement, or may be very slow doing it. Rewinding and forward spacing may be better.) bsr Backwards space count records. The tape is positioned after the last block of the previous file if you hit a filemark when spacing backwards. The block count is set to -1 to indicate that the driver has no idea where it is on the previous file. eom Forward space to the end of media. rewind Rewind the tape. offline, rewoffl Rewind and take offline. This may cause some drives to eject the tape. status Shows the status of the drive, the sense key of the last SCSI error, current file number, current record number, residual count if the last command that encountered end-of-file, and the current block size. retension Removes tape tension by winding and rewinding the tape completely. erase Erases the tape completely and rewinds it. density Sets the density code to read or write the tape to count. Density codes supported depend on the drive. This command need not be used if the drive senses the proper density on read and can only write one density. blksize, blocksize Sets the block size used to read or write the tape to count. This command may be used to select a fixed block size for a variable block size tape. This will speed up I/O for small block sizes. Use a zero count to use variable sized blocks again. ENVIRONMENT
TAPE Tape drive to use if set. FILES
/dev/nrst4 Default tape device. SEE ALSO
mtio(4), st(4). AUTHOR
Kees J. Bot ( MT(1)
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