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Full Discussion: Power failure: file damage?
Top Forums UNIX for Dummies Questions & Answers Power failure: file damage? Post 302895107 by Corona688 on Friday 28th of March 2014 01:30:22 PM
Old 03-28-2014
Quote:
Originally Posted by raylier
~#hello -all,
Many UNIX/Linux/BSD/etc books warn about turn off the puter without a proper shutdown. This can damage files which are open at that moment. Seems logical to me. My question is.. does the system warn you when there are damaged files when the system is up again? I had a power failure this week (twice) while my Linux and freeBSD servers were running. (for study so no power backup). Everything works fine. But is it possible that there are damaged files I don't know of but can cause trouble later on? Thanks for reading.
They will have checked and repaired themselves. It can tell, because it leaves a flag for itself to check whether the filesystem was unmounted safely or not. Your system would refuse to boot if it couldn't repair them.

The damage isn't completely random. It happens when a filesystem operation was left half-finished because of a power-failure or other crash. This means that, if anything happened, things(files or folders) which were being often modified are the most likely to be damaged, truncated, or missing.

This also means that a partition which almost never gets written to is very unlikely to be damaged by a power outage. This is one good reason to split up your system into partitions instead of lumping everything into /...
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FSCK_HFS(8)						    BSD System Manager's Manual 					       FSCK_HFS(8)

NAME
fsck.hfs -- HFS file system consistency check SYNOPSIS
fsck.hfs -q [-df] special ... fsck.hfs -p [-df] special ... fsck.hfs [-n | -y | -r] [-dfgl] [-m mode] [-c size] special ... DESCRIPTION
The fsck.hfs utility verifies and repairs standard HFS and HFS+ file systems. The first form of fsck.hfs quickly checks the specified file systems to determine whether they were cleanly unmounted. The second form of fsck.hfs preens the specified file systems. It is normally started by fsck(8) during systen boot, when a HFS file system is detected. When preening file systems, fsck.hfs will fix common inconsistencies for file systems that were not unmounted cleanly. If more serious problems are found, fsck.hfs does not try to fix them, indicates that it was not successful, and exits. The third form of fsck.hfs checks the specified file systems and tries to repair all detected inconsistencies. If no options are specified fsck.hfs will always check and attempt to fix the specified file systems. The options are as follows: -c size Specify the size of the cache used by fsck.hfs internally. Bigger size can result in better performance but can result in deadlock when used with -l option. Size can be specified as a decimal, octal, or hexadecimal number. If the number ends with a ``k'', ``m'', or ``g'', the number is multiplied by 1024 (1K), 1048576 (1M), or 1073741824 (1G), respectively. -d Display debugging information. This option may provide useful information when fsck.hfs cannot repair a damaged file system. -f When used with the -p option, force fsck.hfs to check `clean' file systems, otherwise it means force fsck.hfs to check and repair journaled HFS+ file systems. -g Causes fsck.hfs to generate its output strings in GUI format. This option is used when another application with a graphical user interface (like Mac OS X Disk Utility) is invoking the fsck.hfs tool. -l Lock down the file system and perform a test-only check. This makes it possible to check a file system that is currently mounted, although no repairs can be made. -m mode Mode is an octal number that will be used to set the permissions for the lost+found directory when it is created. The lost+found directory is only created when a volume is repaired and orphaned files or directories are detected. fsck.hfs places orphaned files and directories into the lost+found directory (located at the root of the volume). The default mode is 01777. -p Preen the specified file systems. -q Causes fsck.hfs to quickly check whether the volume was unmounted cleanly. If the volume was unmounted cleanly, then the exit status is 0. If the volume was not unmounted cleanly, then the exit status will be non-zero. In either case, a message is printed to standard output describing whether the volume was clean or dirty. -y Always attempt to repair any damage that is found. -n Never attempt to repair any damage that is found. -r Rebuild the catalog file on the specified file system. This option currently will only work if there is enough contiguous space on the specified file system for a new catalog file and if there is no damage to the leaf nodes in the existing catalog file. SEE ALSO
fsck(8) BUGS
fsck.hfs is not able to fix some inconsistencies that it detects. HISTORY
The fsck.hfs command appeared in Mac OS X Server 1.0 . Mac OS X November 21, 2002 Mac OS X
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