mt command questions

Jerry McAllister jerrymc at
Wed Apr 18 19:31:38 UTC 2007

On Wed, Apr 18, 2007 at 09:10:30AM -0400, Lowell Gilbert wrote:

> Sean Murphy <smurphy at> writes:
> > I am learning about backing up to tape and have made quite a bit of
> > progress with the mt command.  I understand what the fsf option does.
> > There are other options however and would like to understand them as
> > well.  I am looking at the man page and have tried googleing them with
> > not a lot of luck.  the fsr and fss options I understand they would
> > fast forward but what is "count records" and "count setmarks"
> > considered and how would I use them?
> In this context, "count" is a number. 
> I haven't used mt(1) in quite a while, but I don't think I ever used
> more than one of {files, records, setmarks} on the same tape,
> andoffhand I can't think of a reason for doing so.  If you only put
> one backup on a given tape, you wouldn't use any of them.

We often put a number of backups on one tape.
It is convenient to make a fill dump on one day and then
incremental dumps for other days.   In that case, the full
dump take a whole tape, but all the incrementals together
take one tape.
Also, when I want to make a system to install on several 
machines via tape, each file system becomes one backup.

The count does refer to the number of operations to do.
So, for example, if you have 5 files one one tape and you
want to go to that last file to restore, then you would execute:
   mt -f /dev/nrsa0 fsf 4
to skip past the first four files to get to the last one.


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