Every night on the servers and on several clients the CGA-Backup is started. Users have the chance to change the behavior vie a file called ‘.cgabackup’, put into the homedirectory. This file can consist of serveral lines:

BACKUP_EXCLUDE tmp/ test/ private/
BACKUP_SUCCESSMAIL 1
BACKUP_MAILTO techn@cg.tuwien.ac.at

The first line shows how to exclude directories (or files) from the backup. In this case the whole Directory without the directories tmp/ test/ and private/ is backuped. There must not be whitespace after the .

BACKUP_SUCCESSMAIL means that every backup produces an e-mail, irrelevant wether the Backup was successful or not.

BACKUP_MAIL sets the E-Mail-Adress to whom the (Error-)Mail is sent (default: user@cg.tuwien.ac.at).

The backups are transferred to the backup server using ‘rsync’. This program generates an exact copy of the original tree, files that are already in the backup are not copied if they are the same (rsync uses checksums to decide wether a files needs to be replaced). Replaced files (files that has been replaced by a newer version or files that have been deleted) are moved to a backup-directory (every day gets a new directory called ‘YYYYMMDD’).
After a defined time (eg. 2 weeks) these backup-directories are deleted.
So it’s possible to regenerate all files during the last 2 weeks.

Every beginning of a month a ‘hardlinked’ copy of the current-tree is generated (if there has been a backup during that month). Hardlinked means that only the directory-structure is duplicated, not the files.
Each file (on a UNIX-filesystem) is a hardlink to some data in the filesystem and you can have several hardlinks to the same data. When a hardlink is deleted the data stays until no hardlinks point there.
So we can make a copy of the data that needs practically no space (just the directory entries has to be created new).

So it’s possible to save several monthly backups. At the moment monthly backups are saved for four months, backups of the quarter of a year (january, april, july, october) are saved for 15 months. The Backups are called ‘M'YYYYMM. ([[CGA-Backup (Server)|more info on the server side]])

All the backups are stored on a RAID, so the failure of a harddisk is no problem for us.

There’s also a webpage, where you can check your backups and also restore data. It’s located on http://backupcga.iemar.tuwien.ac.at. You use your usual UNIX-Password and you have access to your backups.