backup your disk over network using dump and ssh

The traditional UNIX® backup programs are dump and restore. They operate on the drive as a collection of disk blocks, below the abstractions of files, links and directories that are created by the file systems. dump backs up an entire file system on a device. It is unable to backup only part of a file system or a directory tree that spans more than one file system. dump does not write files and directories to tape, but rather writes the raw data blocks that comprise files and directories.

Note: If you use dump on your root directory, you would not back up /home, /usr or many other directories since these are typically mount points for other file systems or symbolic links into those file systems.

dump has quirks that remain from its early days in Version 6 of AT&T UNIX (circa 1975). The default parameters are suitable for 9-track tapes (6250 bpi), not the high-density media available today (up to 62,182 ftpi). These defaults must be overridden on the command line to utilize the capacity of current tape drives.

It is also possible to backup data across the network to a tape drive attached to another computer with rdump and rrestore. Both programs rely upon rcmd(3) and ruserok(3) to access the remote tape drive. Therefore, the user performing the backup must be listed in the .rhosts file on the remote computer. The arguments to rdump and rrestore must be suitable to use on the remote computer. When rdumping from a FreeBSD computer to an Exabyte tape drive connected to a Sun called komodo, use:

# /sbin/rdump 0dsbfu 54000 13000 126 komodo:/dev/nsa8 /dev/da0a 2>&1
Beware: there are security implications to allowing .rhosts authentication. Evaluate your situation carefully.

It is also possible to use dump and restore in a more secure fashion over ssh.

Example 18-1. Using dump over ssh

# /sbin/dump -0uan -f - /usr | gzip -2 | ssh -c blowfish \
targetuser@targetmachine.example.com dd of=/mybigfiles/dump-usr-l0.gz

Or using dump's built-in method, setting the environment variable RSH:

Example 18-2. Using dump over ssh with RSH set

# RSH=/usr/bin/ssh /sbin/dump -0uan -f targetuser@targetmachine.example.com:/dev/sa0 /usr