Backup & Restore Objectives –to understand Unix backup strategies Contents –why have backups –backup terminology –backup media –backup utilities –issues about backup security Practical –to perform backups Summary

Why Backup? BACKUPS ARE USELESS IF THEY CANNOT BE RESTORED Backups help recover data in the event of system failure Allow users to recover accidentally (or deliberately) corrupt or deleted files Used to retain data while systems are upgraded Backups are also be used for transferring data between non- networked machines

When to Backup Use cron to schedule backup scripts to run overnight Backup changing data every day –possibly use a full backup on one day –and incremental backups on the rest –make sure you change tapes every day –don't backup to the same tape all the time # more backup.inc DAY=`date +%a` cd / find etc home var -newer /var/adm/backup.full -print | \ cpio -ocvBO /dev/nst0 2> /var/adm/log.$DAY # more backup.inc DAY=`date +%a` cd / find etc home var -newer /var/adm/backup.full -print | \ cpio -ocvBO /dev/nst0 2> /var/adm/log.$DAY # more backup.full DAY=`date +%a` cd / touch /var/adm/backup.full find etc home var -print | \ cpio -ocvBO /dev/st0 2>/var/adm/log.$DAY # more backup.full DAY=`date +%a` cd / touch /var/adm/backup.full find etc home var -print | \ cpio -ocvBO /dev/st0 2>/var/adm/log.$DAY

Store backups in a lockable fireproof safe –if you don't have one buy one, they're not expensive Unix backups are insecure –there are no access controls –anyone with physical access to the media can restore the data Take backups and archives off-site –backups are no good if they are burnt/flooded with the computer systems –however, remember that data is confidential Don't keep backups immediately next to the machine –at the very least put the backups in a different building or room Where to Store Backups

What to Backup? Backup those files which change on a daily basis: /etcUnix configuration file /varUnix files which vary on a day to day basis /homeuser files –only backup the entire system when needed Backup the entire system on a regular basis –especially before updating the system –before preventative maintenance or moving the hardware Be careful with database systems –databases usually involve several files which must be consistent –stop database systems before backing up their files –some databases have a backup mode used when the system cannot be taken down for backups –databases using raw disks for storage will provide their own backup

Backup Media Traditional backup media is magnetic tape –reel-to-reel (½" or 9-track) –cartridge tape (¼" or SCSI tape) –video-8 (Exabyte) –DAT (Digital Audio Tape) –DLT (Digital Linear Tape) Other media include –removable disk packs (Bernoulli) –WORM disk (Write Once Read Many optical disks) –recordable CD (CD-R/DVD) –rewriteable optical disk (MO, phase change)

Magnetic Tape Magnetic tapes susceptible to magnetic fields –power cables, motors, magnets, etc. Cartridge media degrades with time and use –2 year life span and should be read every 6-12 months –replace tapes after 10 writes (20 at most!) DAT, DLT and Exabyte will last longer –but still have a limited life Needs careful storage –temperate and humidity controlled –sunlight (don't leave on a windowsill) Don't compromise your backups by using cheap or worn media

Optical Disks Optical disks have advantages over magnetic tapes –digital recording –reliable & robust media –compact media –can be treated as disks (no need to use backup utilities) Also have disadvantages –smaller capacity –more expensive media/drives (less true as technology advances) WORM or CD-R is the only choice for long term archives –data that must be kept for more than one year

Unix Backup Terminology Archive –full backup taken off-line (deleted from the system) Image backup –complete copy of a disk or partition Full backup –complete directory backup by files Incremental backup –files changed since last full or incremental backup Dump levels (0-9) –files changed since last backup at same or lower dump level –level 0 dump is a full backup

Backup Utilities File oriented utilities cpio- copy to I/O tar- tape archive and restore Filesystem utilities dump - backup linux filesystems WARNING! OBSOLETE! restore - restore linux dump WARNING! OBSOLETE! dumprx - dump Veritas filesystems restorerx- restore Veritas dump Device level dd- direct device access(image backups) Proprietary utilities –yast backup, SuSE backup –some manufacturers provide their own utilities (AIX: backup & restore) –if you use these you are tied to that manufacturer Third party Applications

Tape Archive and Restore Use tar for quick and simple backups –not flexible enough for sophisticated backup strategies Files are written to the archive in tar format –directory pathname and inode information –user, group and permission information –creation and modification times SCSI Tape device in Linux are usally called: /dev/nst[0-31]rewind /dev/st[0-31]no rewind Dencity modes: -, a, l, m # cd /home/radar # tar cvf /dev/st0. # tar tvf /dev/st0 # cd /tmp # tar xvf /dev/st0 # cd /home/radar # tar cvf /dev/st0. # tar tvf /dev/st0 # cd /tmp # tar xvf /dev/st0

Copy to I/O Use cpio for system backups –supports flexible and sophisticated backup strategies Files are written to the archive in cpio format –directory pathname and inode information –user, group and permission information, creation and modification times cpio -o list of files from stdin writes archive to stdout cpio -it archive read from stdin table of contents to stdout cpio -i archive read from stdin files restored according to archived pathname

Options to cpio General options -v verbose mode -B use large blocks -C n use blocks of n bytes -c use ASCII headers (always use this option)  Specify I/O devices with -O file for better handling of multi-volume media when archiving -I file for better handling of multi-volume media when restoring  Input (restore) options -t list table of contents rather than restore files -d create directories if needed -u unconditionally restore files -m retain file modification times

Exercise - Using cpio Explain the purpose of the following commands? # find. -print | cpio -ovcB >/dev/rmt/0m # cpio -itvcB </dev/rmt/0m # cd /tmp # cpio -ivcdumB </dev/rmt/0m # cd / # find etc home var -print | cpio -ovcB -O /dev/rmt/0m # cd /tmp # cpio -ivcdmB -I /dev/rmt/0m 'etc/init.d etc/rc*.d' # find. -print | cpio -ovcB >/dev/rmt/0m # cpio -itvcB </dev/rmt/0m # cd /tmp # cpio -ivcdumB </dev/rmt/0m # cd / # find etc home var -print | cpio -ovcB -O /dev/rmt/0m # cd /tmp # cpio -ivcdmB -I /dev/rmt/0m 'etc/init.d etc/rc*.d'

Summary Unix provides basic utilities for performing backups tar, cpio dump & restore dumprx & restorerx dd Unix backups are written to the media with their file attributes and pathnames Unix backups are insecure, there are no access control restrictions Keep all backups in a locked temperature and humidity controlled environment Backups are vital to system integrity - keep offsite backups if possible