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Operating Systems AIX Fsck -n on mounted FS - how unreliable ? Post 302925719 by Corona688 on Wednesday 19th of November 2014 12:53:17 AM
Old 11-19-2014
Quote:
Originally Posted by maraixadm
So again, I don't want to modify it live
But you are modifying it live. It's like trying to read a dictionary while someone else is constantly changing the order of the words -- possibly tearing out pages while they're at it, if they're writing to a corrupt filesystem. If you at least made it read-only, stopped moving things around, it'd be possible to check it.

The kernel makes an awful lot of assumptions about the state of the filesystem. It's the job of it and the journal to keep it that way, but if something else unintentionally alters the filesystem tree -- power outage, disk failure, controller glitch, whatever -- these assumptions may be violated, and using it can cause bad things to happen. Like an index pointing to the wrong disk cluster, causing data to be overwritten or two files to unintentionally share contents, or a file just not mentioned at all anywhere and disappearing from disk, etc, etc.

fsck makes as few assumptions as possible, but does assume the filesystem isn't changing. That's the tradeoff it makes.

Last edited by Corona688; 11-19-2014 at 02:19 AM..
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FSCK(1) 						      General Commands Manual							   FSCK(1)

NAME
fsck, fsck1 - perform file system consistency check SYNOPSIS
fsck [-aclmrs] [device] ... OPTIONS
-a Automatically repair inconsistencies -c Check and list only the specified i-nodes -l List the files and directories in the filesytem -r Prompt user for repairs if inconsistencies are found -s List the superblock of the file system EXAMPLES
fsck /dev/hd4 # Check file system on /dev/hd4 fsck -a /dev/at0 # Automatically fix errors on /dev/at0 fsck -l /dev/fd0 # List the contents of /dev/fd0 fsck -c 2 3 /dev/hd3 # Check and list /dev/hd3 i-nodes 2 & 3 DESCRIPTION
Fsck performs consistency checks on the file systems which reside on the specified devices. Fsck1 is an alternate version for use on obso- lete V1 file systems. When either the -a or -r flags are given, the file system will be repaired if errors are found. Before running fsck on a mounted file system, it must first be unmounted. Trying to repair a mounted file system is dangerous and should not be attempted. To repair the root file system (which cannot be unmounted), first type CTRL-F9 at the console to kill any and all processes. Log back in as root, type sync to force any buffered changes to disk, run fsck on the root file system and immediately reboot the computer by typing reboot. It is necessary to kill all processes before repairing the root file system to prevent them from modifying any disk blocks while fsck is running. This is only necessary for the root file system, any other file system can simply be unmounted before it is checked. SEE ALSO
mkfs(1), mount(1). FSCK(1)
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