The mt command

As I told you earlier, just yesterday I discovered the mt command. I know mv, but mt? Well, I then did a man on it. Mt........what the...........magnetic tape control?! I don't believe this! I can control a tape drive from a PC! I can send commands to it! The last time I did this was with a really old Texas Instruments TI-99/4A. Hmmm......I might explore this........

Anyway, let's get back to mt. Its syntax is mt [ -f tapename ] command [ count ]. Command and count will be explained shortly. The tape selecting option is -f, which selects the raw tape device. I believe /dev/rmt is the /dev folder for this. There are also a number of operands for mt. Here are some of them from http://bama.ua.edu/cgi-bin/man-cgi?mt+1, a online copy of the UNIX man pages:

count - The number of times that the requested operation is to be performed. By default, mt performs command once. Multiple operations of command may be performed by specifying count.

command - Available commands that can be sent to a magnetic tape drive. Only as many characters as are required to uniquely identify a command need be specified.

eof, weof - Write count EOF marks at the current position on the tape.

fsf - Forward space over count EOF marks. The tape is positioned on the first block of the file.

fsr - Forward space count records.

bsf - Back space over count EOF marks. The tape is positioned on the beginning-of-tape side of the EOF mark.

bsr - Back space count records.

nbsf - Back space count files. The tape is positioned on the first block of the file. This is equivalent to count+1. bsf's followed by one fsf.

asf - Absolute space to count file number. This is equivalent to a rewind followed by a fsf count.

(the next section is from http://www.computerhope.com/unix/umt.htm)

If count is specified with any of the following commands, the count is ignored and the command is performed only once.

eom - Space to the end of recorded media on the tape. This is useful for appending files onto previously written tapes.

rewind - Rewind the tape.

offline, rewoffl - Rewind the tape and, if appropriate, take the drive unit off-line by unloading the tape. It cycles through all four tapes.

status - Print status information about the tape unit.

retension - Rewind the cartridge tape completely, then wind it forward to the end of the reel and back to beginning-of-tape to smooth out tape tension.

reserve - Allow the tape drive to remain reserved after closing the device. The drive must then be explicitly released.

release - Re-establish the default behavior of releasing at close.

forcereserve - Break the reservation of the tape drive held by another host and then reserve the tape drive. This command can be executed only with super-user privileges.

erase - Erase the entire tape. Erasing a tape may take a long time depending on the device and/or tape. Refer to the device specific manual for time details.

Good, but a bit complicated and technical, as far as explanations. I guess an example (for those of you with tape drives out there) might be:

mt erase - erase the tape in the drive found at /dev/rmt0.

mt -f $RMT_NR eof 1 - Mark the end of the tape.

Very cool. Again, these are just probable examples of mt.

For more info, you can go to that man page I mentioned earlier. Another good place for learning about tapes and Unix is http://www.washington.edu/computing/unix/tapes.html. Also you can go to http://www.computerhope.com/unix/umt.htm for more info on use and syntax. That link also provides a link to a page on tcopy, a command I will be discussing soon. Enjoy!

Command of the week: tar

Sorry I haven't gotten back to posting in sometimes. Anyway, this week's command is tar. Tar, course, stands for TApe aRchive. It is used to compress files into an archive. Its basic syntax goes like this:

tar file.tar file1 file2 file3

What to me is amazing about tar is its vast expanse of options. You can dump directly to a disk in a drive (-cvfz) and do many other interesting things with tar. For the most part, some basic tar functions are -x, extract, -c, create (new archive), -f, file (set tarfile name), -u, update, -t, which leaves a table of contents, and -r, replace. Here are some examples:

tar -xf /foo/capio.tar /foo

Extract the contents of capio.tar into the folder foo.

tar -cvfz /dev/rfd0a prog1.c newstuff.vi httpd.conf

Tar takes over the floppy drive (in NetBSD in this case) and directly writes the following three files to the floppy. It can be change to burn a CD, though, I think.

Still, this is only a basic tutorial. For more, try this site - http://www.computerhope.com/unix/utar.htm

xatapu