03-05-2005
I'm not following all of this, but here are a few comments. Are you sure that /usr is mounted? Are you sure that you don't know the device name? It's not easy to find out that a file system is mounted without also obtaining the device name. For example, with the "df" command, the device name is the first field. You can just examine /etc/fstab to get the device name. But you should not actually need the device name. Modern versions of fsck will look it up in /etc/fstab. So simply:
fsck /usr
really should work.
Ideally you should find some way to umount /usr or arrange that it was never mounted prior to fsck. A boot cd (can linux really boot from a diskette?) would be a good option. You're right that running fsck on a mounted filesystem is very dangerous. This is because some of the data from that filesystem is sitting in buffer cache. When this cache is written out, it will intermix with the data written by fsck and scramble the filesystem. So you need to do the following sequence of commands:
sync
<wait 10 seconds or so>
fsck /usr
reboot -n
The first sync will flush out any changed data in / or any other mounted filesystems. You need to wait until the disk writes complete. Then run fsck.
Then immediately reboot without syncing. Also during this entire procedure, almost nothing else must be happening. It is relatively safe in single user mode. This is not completely safe, but your system is not usuable anyway, so it is what I would try. There is a risk of damaging other mounted filesystems. The first sync together with minimizing activity should mitigate this danger. If you decide to try it, please post back and let us know how it works.
However, even if this does work, you may not be home free. fsck may not be able to repair your disk. "attempt to read blocks from filesystem resulted in short read" make me think that your disk may be bad in a hardware sense. fsck cannot repair broken hardware.
Whether or not fsck seems to work, you must immediately do the "reboot -n". Good luck.
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LEARN ABOUT CENTOS
fsck.gfs2
fsck.gfs2(8) System Manager's Manual fsck.gfs2(8)
NAME
fsck.gfs2 - Offline GFS and GFS2 file system checker
SYNOPSIS
fsck.gfs2 [OPTION]... DEVICE
WARNING
All computers must have the filesystem unmounted before running fsck.gfs2. Failure to unmount from all nodes in a cluster will likely
result in filesystem corruption.
DESCRIPTION
fsck.gfs2 will check that the GFS or GFS2 file system on a device is structurally valid. It should not be run on a mounted file system.
If file system corruption is detected, it will attempt to repair the file system. There is a limit to what fsck.gfs2 can do. If important
file system structures are destroyed, such that the checker cannot determine what the repairs should be, reparations could fail.
GFS2 is a journaled file system, and as such should be able to repair damage to the file system on its own. However, faulty hardware has
the ability to write incomplete blocks to a file system thereby causing corruption that GFS2 cannot fix. The first step to ensuring a
healthy file system is the selection of reliable hardware (i.e. storage systems that will write complete blocks - even in the event of
power failure).
Note: Most file system checkers will not check the file system if it is "clean" (i.e. unmounted since the last use). The fsck.gfs program
behaves differently because the storage may be shared among several nodes in a cluster, and therefore problems may have been introduced on
a different computer. Therefore, fsck.gfs2 will always check the file system unless the -p (preen) option is used, in which case it fol-
lows special rules (see below).
OPTIONS
-a Same as the -p (preen) option.
-f Force checking even if the file system seems clean.
-h Help.
This prints out the proper command line usage syntax.
-q Quiet.
-n No to all questions.
By specifying this option, fsck.gfs2 will only show the changes that would be made, but not make any changes to the filesystem.
-p Preen (same as -a: automatically repair the file system if it is dirty, and safe to do so, otherwise exit.)
Note: If the file system has locking protocol lock_nolock, the file system is considered a non-shared storage device and the fsck is
deemed safe. However, fsck.gfs2 does not know whether it was called automatically from the init process, due to options in the
/etc/fstab file. Therefore, if the locking protocol is lock_dlm and -a or -p was specified, fsck.gfs2 cannot determine whether the
disk is mounted by other nodes in the cluster. Therefore, the fsck is deemed to be unsafe and a warning is given if any damage or
dirty journals are found. In that case, the file system should be unmounted from all nodes in the cluster and fsck.gfs2 should be
run manually without the -a or -p options.
-V Version.
Print out the program version information.
-v Verbose operation.
Print more information while running.
-y Yes to all questions.
By specifying this option, fsck.gfs2 will not prompt before making changes.
fsck.gfs2(8)