maintain an effective data backup strategy
backup types
backup are usually run in one of three general foems:
full backup a full, or complete backup saves all of the files on your system.
differential backup save only files that have been modified or created since the last full backup. compared to full backup,differentials are relatively fast because of the reduced number of files written to the backup media.
incremental backup save only files that have been modified or created since the last backup, including the last incremental backup.these backups are alse relatively fast.
device files
when performing backup operations to tape and other removable media, you must specify the device using its device file. these files are stored in /dev and are understood by the kernel to stimulate the use of device drivers that control the device. here are some typical devices files you may find on linux system:
/dev/st0 first SCSI tape drive
/dev/ft0 first floppy-controller tape drive,such as travan drives
/dev/fd0 first floppy disk drive
/dev/hdd an ATAPI Zip or other removable disk.
backup operations
what shoule I back up?
It's impossible to describe exactly what to back up your system. if you have enough time and media, complete backups of everything are safest. However, much of the data on a linux system, such as commands, libraries, and manpages don't change routinely and probably won't need to be saved often. making a full backup of the entire system makes sense after you have installed and configured your system. once you have created a backup of your system, there are some directories thta you should routinely(经常性的) backup:
/etc Most of the system configuration files for a linux system are stored in /etc, which should be backed up regularly.
/home User files are stored in /home, depending on your configuration, you may also store web server files in /home/httpd. On multiuser system or large web servers, /home can be quite large.
/usr/src If you have done any kernel compilation, back up /usr/src to save your work.
/var/log If you have security or operational concerns, it may be wise to save log files stored in /var/log
/var/spool/mail If you have use email hosted locally, the mail files are stored in /var/spool/mail and should be stained.
/var/spool/at and /var/spool/cron User's at and cron files are stored in /var/spool/at and /var/spool/cron, respectively. These directories should be retained if these services are available to your users.
Of course,the list is just a start, as each system will have different backup requirements.
when via cron using a shell script to backup, you must guarantee your system running in single user. If users or processes are actively working in a file system as it is backed up, the state of the files in the archive will be in question. To avoid this problem. It may be satest to elimilate the users and processes from the backup scheme completely by putting linux into single-user mode(runlevel 1) before executing the backup. In the mode, users will not be logged on, and servers, such as web or database servers, will be shutdown. With no active process running, the filesystem can be safely backed up.
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