|What is it?||Backup commands.||other issues||Media, Hardware|
Why do we need backups?
In order to recover lost files we need to have backups. Why do we use computers? so that we can store and manipulate our data. So if our data is lost computers are of no use. Thus giving us a reason to copy the data into a backup media, from which we can recover our lost files after disaster. Before backing up the files, a systems administratore needs to decide.
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These are common backup and restore commands used in
all favours of Unix.
Backup and restore (storage) Commands compress uncompress, cpio,dump, restore , pack, tar, mt.
Compress command compresses a file and returns the original file with .z extension, to uncompress this filename.Z file use uncompress filename command. syntax for compress command is
compress options files
Uncompress file uncompresses a file and return it to its original form.
uncompress filename.Z this uncompresses the compressed file to its original name.
cpio command is useful to backup the file systems. It copy file archives in from or out to tape or disk, or to another location on the local machine. Its syntax is
cpio flags [options]
Dump command is useful to backup the file systems.
dump command copies all the files in filesystem that have been changed after a certain date. It is good for incremental backups. This information about date is derived from /var/adm/dumpdates and /etc/fstab .
syntax for HP-UX dump is
/usr/sbin/dump [option [argument ...] filesystem]
Restore and ufsrestore command restores files backed up with dump command.
restore options arguments files-dirs
pack command compacts each file and combine them together into a filename.z file. The original file is replaced. Pcat and unpack will restore packed files to their original form.
Pack options files
tar command creates an archive of files into a single file.
Tar copies and restore files to a tape or any storage media. Synopsis of tar is
tar [options] [file]
tar cvf /dev/rmt/0 /bin /usr/bin creates an archive of /bin and /usr/bin, and store on the tape in /dev/rmt0.
tar tvf /dev/rmt0 will list the tape's content in a /dev/rmt0 drive.
tar cvf - 'find . -print' > backup.tar will creates an archive of current directory and store it in file backup.tar.
Mt command is used for tape and other device functions like rewinding, ejecting, etc. It give
commands to tape device rather than tape itself. Mt command is BSD command and is seldom found
in system V unix versions.
mt [-t tapename] command [count]
These following are some other issues concerning backups.
Magnetic tapes are the most used media for backup. 8mm and 4mm tapes are most common backup
medium for Unix systems. 8mm tapes were originally designed for video uses (8mm video camcorder),
media holds upto 2GB of data. If your system needs more then 1 tape for backup then a stacker
which can hold upto ten tapes along with software is very common. 4mm tapes which are smaller
can hold more data since it is newer technology, upto 4GB. Another type of very famous
upcoming media is DLT tapes, DLT tapes normally comes with all the hardware and software. All
you have to do is make sure that there are enough tapes and schedule the backup.
Floppy disks are found on most computer systems. Very inexpensive and reliable but their
capacity is very small. Floppy disks are only good for emergency booting of system. Backup
on floppies can run into several hundred or thousands of floppies each time.
Disk mirroring capabilities make it a very fast and reliable backup system.
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