Ubuntu: How to add or append a file to an existing tape backup

  Sometimes you may with to add files to an existing backup; if you issue a command like:  
tar -cvf /dev/st0 backupfiles
  …and the tape is not already set to the end of the previous archive you will over-write any data from the position on the tape. Use the “eom” command to move the tape to the end of the alread-recorded files like so:  
mt -f /dev/[path-to-tape] eom
mt -f /dev/st0 eom
  Now you can use tar to add a file to the tape without over-writing the existing data.