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Top Forums UNIX for Dummies Questions & Answers about fsck Post 302324580 by vbe on Thursday 11th of June 2009 06:58:11 AM
Old 06-11-2009
The secret of UNIX's speed is its buffers... and the main reason you must NEVER turn off a UNIX system by power off - It needs a clean shutdown in order to flush the buffers write to disk any pending write and unmount cleanly all file sytems in order to set the "clean" flag for next reboot...
Total buffer size depends on the system but can reach the GB 400-600 MB is common...

And so after a crash or dirty shutdown, it can take ages at next reboot for the system to come up (yes hours... in fsck...). And then came JFS - what a relief..
There are good books on the subject you know...
To make it simple : See JFS (like VXFS) as a database (oracle?), in case of crash it knows how to recover and if cant totally, will drop the last transaction in order to be in a coherent state...
 

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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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