Sometimes files or entire directory trees are accidentally removed or corrupted so that it is desirable to retrieve old versions of them. Because of the multi-user nature of the Unix systems at UVa, when a file is deleted, that file cannot be recovered by an "undelete" command. There are a couple of options available, however, for getting a file or files restored.
If you log into the blue.unix cluster to access your account, the "snapshot" utility is available to you for retrieving deleted files. This utility can be accessed from within Umenu as well as from the Unix prompt. "Snapshot" may be used to retrieve versions of files which are less than one week old. For example, if you accidentally removed a file on 6/7, you could restore the file as it existed on 6/1, 6/2, 6/3, 6/4, 6/5 or 6/6, or even earlier in the day on 6/7. To go back farther than one week, files must be restored from backup tapes (see the section below). For detailed information about using the snapshot command, please see the document: Retrieving Deleted Files on a Unix Machine
Most files on ITC-supported Unix machines are backed up nightly to magnetic tape. Versions of files on tape are typically retained for two years. Exceptions are mailbox files, which are only retained for 21 days.
Restoring a file, or files, from tape is a manual task that must be performed for you by a member of the Computing Support Services Division of ITC. Because the restoration involves time and effort on your behalf by an ITC staff member, it is not a request that should be made lightly. The ITC tape backups are a service provided for emergencies, not an archiving service. They cannot adequately take the place of your own careful attention to keeping your own backups of important data.
Before you make a restore request, first determine whether you can without too much difficulty recreate or obtain another copy of the file that you have lost. If this is not possible, you need to gather some information about the lost or corrupted file(s):
When you have gathered this information, you should email it in a request to consult@virginia.edu, along with the information on the file.
Three times a year, most files on Unix disks are copied to magnetic tape. This is known as a full, or level 0, dump and takes so long that it cannot be done very often. To be able to provide nightly backups of the files, a hierarchy of incremental backups is used. Monthly (level 3), weekly (level 5), and daily (level 7) backups are performed. For example, when a level 3 backup is performed, the last change date of each file currently on disk is compared to the date of the last level 0 backup. If a file's change date is more recent than the level 0 backup, the file is copied to tape as part of the level 3 backup. In this system, level 7 backups are usually based on level 5 backups, which are based on level 3 backups, which are based on level 0 backups. In effect we are ``skimming'' the disks for files that have been changed since the last backup.
Daily backups are nominally retained for a month, weekly backups for two months, monthly backups for 4 months, and semester backups for two years. This scheme makes it possible to restore any file as it existed on any particular day up to 30 days ago. Beyond this, any file can be restored as it existed in any particular week up to two months ago. Any file can be restored as it existed in any particular month up to 4 months ago. Any file can be restored as it existed in any particular semester up to 2 years ago. It is important that you request a file restore as soon as possible after you lose the file because backup tapes are recycled.
Please help us to help you by giving us the most accurate date information that you can for the files that you need restored.