Running e2fsck on a mounted filesystem

I know, running fsck on a mounted filesystem is utterly unrecommended. The command warns you (it actually frightens you) with the following message:

# fsck /dev/VolGroup00/LogVol00
fsck 1.41.4 (27-Jan-2009)
e2fsck 1.41.4 (27-Jan-2009)
/dev/VolGroup00/LogVol00 is mounted.  

WARNING!!!  Running e2fsck on a mounted filesystem may cause
SEVERE filesystem damage.

Do you really want to continue (y/n)? no

check aborted.

But sometimes I need to check a filesystem in a remote host, so I cannot boot from a liveCD to run fsck in the unmounted device. Looking for an option allowing me to overcome this nuisance I found the following in e2fsck’s man page:

Note  that  in general it is not safe to run e2fsck on mounted filesys-
tems.  The only exception is if the -n option is specified, and -c, -l,
or  -L  options  are not specified.

Using e2fsck instead of fsck is not a problem because it checks ext2 and ext3 filesystems and mine are ext3 (fsck checks and optionally repairs a lot of filesystem types).

Let us see what the man page says about the -n option:

-n     Open the filesystem read-only, and assume an answer of  `no'  to
       all  questions.   Allows  e2fsck  to  be used non-interactively.
       (Note: if the -c, -l, or -L options are specified in addition to
       the -n option, then the filesystem will be opened read-write, to
       permit the bad-blocks list to be  updated.   However,  no  other
       changes will be made to the filesystem.)  This option may not be
       specified at the same time as the -p or -y options.

So it seems to be safe running it with that option. But the e2fsck man page also states (dealing with the safe check):

However, even if it is safe to do
so, the results printed by e2fsck are not valid if  the  filesystem  is
mounted.    If e2fsck asks whether or not you should check a filesystem
which is mounted, the only correct answer is ``no''.  Only experts  who
really know what they are doing should consider answering this question
in any other way.

So, I use it only when I want to know if there is something wrong with the filesystem. I run it with the -f option too which forces checking even if the file system seems clean.

# e2fsck -fn /dev/VolGroup00/LogVol00 
e2fsck 1.41.4 (27-Jan-2009)
Warning!  /dev/VolGroup00/LogVol00 is mounted.
Warning: skipping journal recovery because doing a read-only filesystem check.
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
F10-i686-Live: 123335/475136 files (3.8% non-contiguous), 876070/1900544 blocks

If the output is like above all is OK, but if the device has errors, then you will need to run fsck with the filesystem unmounted.

speak up

Add your comment below, or trackback from your own site.

Subscribe to these comments.

Be nice. Keep it clean. Stay on topic. No spam.

You can use these tags: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>

*Required Fields