Let’s have closer look at how to resolve Centos fsck failed with error code 4, with help of Server management support services. We Bobcares respond with details to all your queries no matter how minor.

How to fix Centos fsck failed with error code 4

Error:

systemd-fsck[605]: /dev/sda2: UNEXPECTED INCONSISTENCY; RUN fsck MANUALLY.
systemd-fsck[605]: (i.e., without -a or -p options)
[ 13.652068] systemd-fsck[605]: fsck failed with error code 4.
Welcome to emergency mode. Use "systemctl default" or ^D to activate default
mode.
Give root password for maintenance
(or type Control-D to continue):

In this case /dev/sda2 is my root partition and since it’s mounted even in maintenance mode, attempting to run fsck on it would output:

fsck.ext4 /dev/sda2
e2fsck 1.42.7 (21-Jan-2013)
/dev/sda2 is mounted.
e2fsck: Cannot continue, aborting.

Running fsck on a mounted file system will most damage to it.

Method 1:

Your best option simply is to boot into another Linux as a different partition. Run fsck manually on the faulty partition. This can easily unmount because no OS is using it.

Method 2:  If you cannot boot into another Linux.

Run fsck in dry-run mode. Next pipe the output to make reading more practical:

fsck.ext4 -n /dev/sda2 | more

From there, there will be no critical files damaged and it’s always a gamble to use a corrupted file system.  Next proceed to boot for the system to make some backups. Forcing the system to boot, by creating a file named forcefsck and writing “Y” to it. echo y > /forcefsck.

At root no longer works and adding fsck.mode=force on the kernel command line, did not fix the problem as fsck will not fix errors without authorization. ie: if someone enters Yes on the keyboard.

Further, it is possible to fix errors on a read-only file system which can also be used to boot into. Here is the technique:

• Put the root partition into read-only mode. This can be done by modifying the faulty partition’s line on /etc/fstab. But remember your old settings:

UUID=fd1d0fad-3a4c-457f-9b5e-eed021cce3d1 /                       ext4    remount,ro        1 1. 

• If you’re already in maintenance mode. You may able to remount your file system in read-only mode by running “mount -o remount,ro /” and skipping the reboot.

• Reboot.

• Switch to run level1 to minimize the amount of interfering processes. You can skip this step if you’re running the session over SSH: init 1

• Fix the file system by replacing /dev/sda2 with the partition’s device, this should now work. Because the root partition will be in read-only: fsck /dev/sda2.

• Reboot.

• Make the root file system readable/writable: mount -o remount,rw /dev/sda2

• Restore your /etc/fstab to its original state.

• Reboot.

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Conclusion

To sum up, your system is now safe to use again. If errors keep occurring, it’s probably a sign that your hard drive is failing and before you lose it completely.  You should copy your data to a new one.