fbackup header

 
Vince Ungaro
Occasional Advisor

fbackup header

Hi,

I am trying to use fbackup for scripted backups and am running into a problem with the header. In the man page it says that fbackup reserves 1024 bytes for ASCII header info. So I use dd to write a 1024 byte ASCII header to the tape the do a backup using fbackup. All that works find until I tried and either read the contents of the tape or do a restore.

Am I not allowed to write to the header? Can I skip the header check fbackup does somehow? Thanks!
3 REPLIES 3
Patrick Wallek
Honored Contributor

Re: fbackup header

You don't want to do anything to the tape prior to running fbackup.

By default, fbackup will rewind the tape and start from the beginning.

I recommend NOT doing the dd. Just put the tape in and run your fbackup.
Vince Ungaro
Occasional Advisor

Re: fbackup header

Will take above suggestion into consideration
Bill Hassell
Honored Contributor

Re: fbackup header

fbackup is like all commercial backup programs - the tape contents are completely under control of the program. The very first thing that fbackup does is to rewind the tape. It then reads the first records on the tape to see if the tape is an fbackup volume and if so, whether it is part of the current backup set. If the header shows that it is a previously written volume from the same backup job, fbackup rejects the tape.

So no matter what you write on the tape, it will be erased by fbackup because the index at the front of the tape always matches the contents. It is also the reason that you cannot append fbackup runs onto the same tape.

The header referred to in the man page can be read with dd to see what it looks like, or just use frecover to see it:

frecover -V - -f /dev/rmt/


Bill Hassell, sysadmin