what program to use to upack log files ?

[robert]

Hi there,
this sounds stupid but ..

I am not able to unpack archives that have been created by the ubuntu 
log schedular.
At leas not in a bash shell.

root at salome:~/tmp# tar xvfz mail.log.3.gz
tar: This does not look like a tar archive
tar: Skipping to next header
tar: Exiting with failure status due to previous errors


however, using file-roller, I can ..

what is the correct syntax/programm to use for the job?

thanks
robert