====== How to perform a fsck (File System Check) on a system disk ======

Sometimes errors occur on the filesystem of your server's system disk that prevent it from working properly.

In this case, the only solution is to perform a filesystem check to (hopefully) fix the errors.

<note warning>The ''fsck'' on a disk must be done while it is unmounted or in read-only mode. If not, the risk of losing data is very high! Always check the state of the disk before beginning the check and carefully read any warnings produced by the program.</note>

There are two ways of proceeding with the check of the system disk depending on whether you have shell access or not.

===== If you can access a shell to execute commands: =====

If you can log in on your server and get to a shell, then you will be able to proceed to the checking on the disk directly from your server.

==== Switch the disk to Read-Only ====

First of all, you must switch the system disk into read-only mode with the following command: 

  # mount -o remount,ro /

<note tip>
If you get the message ''mount: / is busy'' in return, it means the disk is in use by some programs. You will have to stop or kill the process who have ''w/u'' on ''/''. The command ''lsof /'' will display that information, as in the example below:

<code># lsof /
COMMAND   PID   USER  FD  TYPE DEVICE SIZE/OFF  NODE NAME
rsyslogd  1237  root  3u  REG  202,1  3762377   3544 /var/log/syslog
rsyslogd  1237  root  5w  REG  202,1    29569  25879 /var/log/messages
rsyslogd  1237  root  6w  REG  202,1  2217748  25872 /var/log/auth.log
rsyslogd  1237  root  7w  REG  202,1 36729452  17350 /var/log/daemon.log
rsyslogd  1237  root  9w  REG  202,1   978650  25878 /var/log/user.log
rsyslogd  1237  root 10w  REG  202,1     8108  12417 /var/log/kern.log
</code>

In the case above, we can see that that ''rsyslogd'' is using the system disk in read-write. Therefore, you just have to stop or kill ''rsyslogd'', as well as all other processes having ''w/u'' on ''/''.

</note>

Next, check that the disk has been mounted correctly in read-only mode (''ro'') with the ''mount'' command:

  # mount
  /dev/xvda1 on / type ext4 (ro,noatime,errors=remount-ro)


==== Proceed to the fsck ====

To begin the ''fsck'', execute the following command: 

  # fsck -f /dev/xvda1

The output might look something like this:

<code>
fsck from util-linux 2.20.1
e2fsck 1.42.5 (29-Jul-2012)
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
DEBIAN7_64: 32869/196608 files (0.2% non-contiguous), 274868/786432 blocks
</code>

===== If the shell is unavailable on your server =====

If the shell is not available on your server, you will have to check the disk from another Gandi server. Indeed, this is one of the advantages of server virtualization, which allows you to attach a disk to another server.

To create a new server, you must have sufficient resources (at least one share) available in your Gandi account.

<note tip>
When you buy a share, be sure not to select the "Obligation" checkbox. That way, once the filesystem has been repaired, you can delete the new server and release the share for a prorated refund. 
</note>

Once you get the share, create a new server (in expert mode) using the Linux distribution of your choice. The creation of the new server might take a few minutes.

Once the new server has been created, stop the server with errors on the filesystem. Then detach the system disk and [[en:hosting:manage-disk:attach-disk|attach it]] to the newly created server.

==== Unmount the system disk attached to the new server ====

Once the system disk is attached to the new server, it should be mounted automatically. You can verify that with the ''mount'' command :

<code>
# mount
/dev/xvda1 on / type ext4 (rw,noatime,errors=remount-ro)
/dev/xvdk on /srv/DEBIAN7_64 type ext4 (rw,nosuid,nodev,noatime)
</code>

In the case above, the label of the system disk to check is 'DEBIAN6_64'. To unmount the disk, execute this command: 

  # umount /srv/label_of_the_disk

==== Proceed to the fsck ====

Once the disk has been unmounted, you can proceed to the check of the system disk with the command ''fsck -f /dev/xvdX'' (where ''X'' is the disk to check):

<code>
# fsck -f /dev/xvdk
fsck from util-linux-ng 2.17.2
e2fsck 1.41.12 (17-May-2010)
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
DEBIAN7_64: 32869/196608 files (0.2% non-contiguous), 274868/786432 blocks
</code>