fsck

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Revision as of 16:53, 11 August 2013 by Bwid (Talk | contribs) (Checking: include info from falconindys bbs post about fsck on boot (mkinitcpio vs. systemd))

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Summary help replacing me
Information on how to use fsck.
Related
Ext4
Btrfs
fstab

fsck stands for "file system check" and it is used to check and optionally repair one or more Linux file systems. Normally, the fsck program will try to handle filesystems on different physical disk drives in parallel to reduce the total amount of time needed to check all of the filesystems (see: man fsck).

The Arch Linux boot process conveniently takes care of the fsck procedure for you and will check all relevant partitions on your drive(s) automatically on every boot. Hence, there is usually no need to resort to the command-line unless necessary.

Boot time checking

Mechanism

There are two players involved:

  1. mkinitcpio offers you to option to fsck your root device before mounting it via the fsck hook. If you do this, you should mount root read-write via the appropriate 'rw' option on the kernel commandline.
  2. systemd will fsck all filesystems assuming three things are true: the filesystem has a fsck pass number greater than 0 (either from /etc/fstab or a user-supplied unit file), the filesystem is not already mounted read-write, and you've not elected to disable fsck entirely via the kernel commandline option fsck.mode=skip.
Note: Option 1 is the recommended default, and what you will end up with if you follow the Installation Guide. If you want to go with option 2 instead, you should remove the fsck hook from mkinitcpio.conf and use 'ro' on the kernel commandline.

Forcing the check

The filesystem can be checked by creating a forcefsck file on the partition you wish to check later. For example, for the root partition it would be:

# touch /forcefsck

When you're ready, reboot and fsck will do the rest. And don't worry, this file will be removed automatically when the process is finished.

Alternatively, you can also force fsck at boot time by passing, as a kernel parameter:

# fsck.mode=force

This will check every filesystem you have on the machine.

Tips and tricks

Cancelling the process

Tango-inaccurate.pngThe factual accuracy of this article or section is disputed.Tango-inaccurate.png

Reason: Doesn't work. Tried adding FILES="/etc/e2fsck.conf" to mkinitcpio.conf and rebuilding the initramfs images, but still nothing. --DSpider, 12 January 2013 (Discuss in Talk:Fsck#)

To cancel a running fsck check during boot time, create the following file:

/etc/e2fsck.conf
[options]
allow_cancellation = true

Now you should be able to cancel it with Template:Keypress.

Attempt to repair damaged blocks

To automatically repair damaged portions, run:

Warning: This will not ask if you want to repair it, as the answer is Yes when you run it.
# fsck -a

Repair damaged blocks interactively

Tip: This is useful for when file on the boot partition have changed, and the journal failed to properly update. In this case, unmount the boot partition, and run the following code:

To repair damaged portions, run :

# fsck -r <drive>

Changing the check frequency

By default, fsck checks a filesystem every 30 boots (counted individually for each partition). To change the frequency of checking, run:

# tune2fs -c 20 /dev/sda1

In this example, 20 is the number of boots between two checks.

Note that 1 would make it scan at every boot, while 0 would stop scanning altogether.

Tip: If you wish to see the frequency number and the current mount count for a specific partition, use:
# dumpe2fs -h /dev/sda1 | grep -i 'mount count'

fstab options

fstab is a system configuration file and is used to tell the Linux kernel which partitions (file systems) to mount and where on the file system tree.

A typical /etc/fstab entry may look like this:

/dev/sda1   /         ext4      defaults       0  1
/dev/sda2   /other    ext4      defaults       0  2
/dev/sda3   /win      ntfs-3g   defaults       0  0

The 6th column (in bold) is the fsck option.

  • 0 = Do not check.
  • 1 = First file system (partition) to check; / (root partition) should be set to 1.
  • 2 = All other filesystems to be checked.

Troubleshooting

Can't run fsck on a separate /usr partition

  1. Make sure you have the required hooks in /etc/mkinitcpio.conf and that you remembered to re-generate your initramfs image after editing this file.
  2. Make sure that the bootloader has ro on the "APPEND" line in /boot/syslinux/syslinux.cfg (for Syslinux). GRUB doesn't need one; it is added automatically when you generate a .cfg. For an explanation as to why you need "ro", see this post.
  3. Check your fstab! Only the root partition needs "1" at the end, everything else should have either "2" or "0". Carefully inspect it for other typos, as well.

ext2fs : no external journal

There are times (due to power failure) in which an ext(3/4) file system can corrupt beyond normal repair. Normally, there will be a prompt from fsck indicating that it cannot find an external journal. In this case, run the following commands:

# umount <directory>;  ## unmount the partition based on its directory
# tune2fs -j /dev/<partition>;  ## write a new journal to the partition
# fsck -p /dev/<partition>;  ## run an fsck to repair the partition