Backups in Linux

Ning Zhu

Class presentation

Introduction

• The dump and restore commands are the most common way to create and restore from backups in Linux

• Some other programs also can be used to backup the files. Such as: tar, cpio and dd

Advantage of dump

• Backups can span multiple tapes

• Files of any type can be backed up and restored

• Permissions, ownerships, and modification times are preserved

• Files with holes are handled correctly

• Backups can be performed incrementally

Limitation of dump

• Every filesystem must be dumped individually

• Only filesystems on the local machine can be dumped

Features (dump)

• Support “incremental” backup. Backup level will be assigned to implement this.

• Don’t care about the length of the filenames.

flags to dump

• -u: causes dump to automatically update /etc/dumpdates when the dump completes. The date, dump level and filesystem name are recorded.

• -f: indicates where dump sends the output

• -B: tells dump what is the tape length can be used to dump the files.

# dump -5u –B 800000 –f /dev/sto /work

Dump Schedule

• Simple schedule: Do level 0 dumps of every filesystem each day. Reuse a group of tapes, but every N days, keep the tape forever.

• Moderate schedule: assign a tape to each day of the week, each week of the month, and each month of the year. Every day, do a level 9 dump to the daily tape. Every week, do the level 5 dump. And every month, do a level 3 dump. Do a level 0 dump whenever the incrementals get too big to fit on one tape.

Restore the files using restore

• Restore individual files

• Restore entire filesystems

Restoring individual files

Restore the file /users/rdeaton/lostfile from a remote tape drive for user Dr. Deaton:# mkdir /var/restore# cd /var/restore# rsh tapehost mt –f /dev/nst0 fsf 3# rrestore –i –f tapehost:/dev/nst0restore> lsrestore> cd rdeatonrestore> add lostfilerestore> lsrestore> extract

Restoring individual files (cont’)

Give the file to rdeaton:# cd /var/restore

# ls rdeaton

# ls ~rdeaton

# cp –p rdeaton/lostfile ~rdeaton/lostfile.restored

# chown rdeaton ~rdeaton/lostfile.restored

# rm –rf /var/restore

# mail rdeaton

Your file lostfile has been restored and has been placed in

/users/rdeaton/lostfile.restored

Restoring entire filesystems

• Create and mount the target filesystem

• cd to the mount point of the new filesystem

• Put the most recent level 0 dump in the tape drive

• Type restore –r

• After the level 0 dump has been restored, mount and restore the incremental dumps.

Determine which dumps to restore

0 0 0 0 0 0

0 5 5 5 5

0 3 2 5 4 5

0 9 9 5 9 9 3 9 9 5 9 9

0 3 5 9 3 5 9

Restore expamle

If the most recent dump was the first monthly after

the annual level 0 in the “moderate” schedule, the

commands to restore /home, residing on the

physical device /dev/sda1# /etc/mke2fs /dev/sda1 QUANTUM_PD1050S

# /etc/mount /dev/sda1 /home

# cd /home

/* mount first tape of level 0 dump of /home */

# restore –r

/* mount first tape of level 3 monthly dump */

# restore –r

Other Archiving Programs tar

• tar: package files

tar reads multiple files or directories and packages them into one file, often a tape file. tar is useful way to back up any files whose near-term recovery you anticipate.

Other Archiving Programs cpio

• cpio: archiving utility from ancient times

cpio is similar to tar in functionality. It’s rarely used today. Like tar, cpio can be used to move directory trees.

Other Archiving Programs dd

• dd: twiddle bitsdd is a file copying and conversion program. dd just copies from its input file to its output file. If a user brings you a tape that was written on some non-Linux system, dd may be the only way to read it.dd was to create a copy of an entire system. However, restore and dump is a better option these days.