FYI. Two small corrections: I instead of i and command instead of cammand.
Look in section 5.2 for how to perform incremental dumps. Look at the -g or -G options. They allow you to create a listed-incremental timestamp file when creating an archive. You can also use the --newer option instead to create an incremental backup of files newer than the date argument you supply.
Another method is to use the find command to locate files after a particular date and create a list of files to backup.
The -g and -G options may be GNU extensions. Also pay attention to attribute and posix acl support with your version of tar. You may want to use the "star" program instead if tar won't backup posix acl's or attributes.
There are different ways you could indicate which directories to backup. You can include them in the arguments to the tar command, or you can use the DIR_LIST environmental variable.
Depending on the size of your tapes and the amount you need to backup, you may need to use --multi-volume option to create an archive on multiple tapes.
You said you wanted differential backups. The difference between differential backups and incremental backups is that differential backups save all changes since the first full backup. An incremental backup saves changes since the last backup. So subsequent incremental backups are smaller, but they need to be restored in sequence. You only need to perform a full restore and the last differential backup.
If you use the first named snapshot file when performing a differential backup, that would be the same as performing a differential backup.
I don't own a tape device and don't have experience using the "mt" or "rmt" command. You may need to run an "mt" command before the tar command to cue the tape where it needs to be. Different tape devices may need different options as well. And you may need to track which archive on the tape to cue up to.
You might consider using the source for tar to create a print-worthy ps or pdf version of the info manual from the .texi docbook source.
Last edited by jschiwal; 02-26-2008 at 04:53 AM.