Native Linux (and Unix) Backup Tools

There are several backup tools that are available natively for Unix. Each has their strengths and weaknesses. They appear as they are today after several years of evolution and refinement. The native utilities are:

• tar
• cpio
• dump

The following table compares each of their strengths and weaknesses ¹

Feature	tar	cpio	dump
Simplicity of invocation	Very Simple (tar c files)	Needs find to specify filenames	Simple--few options
Recovery From I/O errors	None--write your own utility	Resync option on HP-UX will cause some data loss	Automatically skips over bad section
Back up special files	Later revisions	Yes	Yes
Multivolume backup	Later revisions	Yes	Yes
Back up accross network	Using rsh only	Yes	Yes
Append files to backup	Yes (tar-r)	No	No
Multiple independent backups on single tape	Yes	Yes	Yes
Ease of listing files on the volume	Difficult--must search entire backup (tar-t)	Difficult--must search entire backup (cpio-it)	Simple--index at front (restore -t)
Incremental backup	No	Must use find to locate new/modified files	Incremental of whole filesystem only, multiple levels
List files as they are being backed up	tar cvf 2logfile	Only after backup with restore -t logfile	(dump can show % complete, though)
Back up based on other criteria	No	find can use multiple criteria	No
Restore absolute pathnames to relative location	Only by using chroot	Limited with cpio-I	Always relative to current working directory
Compatibility	Multiple platform	Multiple platform with ASCII header, not always protable	Readable between some platforms, but cannot be relied on
Primary usefulness	Individual user backup, transfer files between filesystems	System backup, transfer files between filesystems	System backup
Volume efficiency	Medium, usually limited to 10 K block size	Medium, usually only 5 K block size, but can specify larger size on some OSes	High, can usually specify up to maximum block size of device
Wildcards on Restore	No	Yes	only in interactive mode
Simplicity of selecting files for backup from numberous directory	Low--must specivy each independent directory, subdirectories included	Medium--find options	None--will back up one and only one filesystem

Generally, if you had your choice of native backup tools, dump should probably be your best choice. Not only is it relatively simple to use, it also has a great amount of functionality built in. This leaves the administrator free to think more about what he wants to back up and less about how he needs to back it up. Dump also spawns several processes, making it faster. Finally, Dump provides a mechanism built in for interactive file recovery. The syntax of dump is as follows:

dump levelunbdsf blkg-factor density size device-name file_system

1. 0-9 Specifies the level of backup that dump should perform.
2. b Specifies the blocking factor that dump should use.
3. u Tells dump to update the dumpdates file.
4. n Tells dump to notify the members of the operator group when a dump is completed.
5. d and s Tell dump how large the backup volume is.
6. f tells dump what device to use.
7. W,w little used options tell dump to perform a dry run.

Fortunately, with Linux you can usually simply perform the following:

/sbin/dump -0u -f /dev/st0 /your/filesystem/to/backup

To get a list of the files from the tape, enter this:

restore -t /dev/st0

Of course, you can pipe this output out to a file.