Monday, July 29, 2013

Linux -- IO Error on boot read failed, No such File or directory /dev/, Dropping you to a shell, error occurred during the file system check

Filesystem check errors can prevent Linux from booting.
When the Linux system boots, the boot process checks the root filesystem and mounts it read/write.
Note it was mounted by the kernel as read-only).. It basically checks the filesystems with fsck command.

If these filesystem check is failed for root filesystem or any other filesystems presented in fstab, following prompt appears and Linux start process drops the user into a shell to correct the errors..

***An error occurred during the file system check.
***Dropping you to a shell; the system will reboot
***when you leave the shell.
Give root password for maintenance
(or type Control-D for normal startup):
This is a troubling event, particularly because it might well appear if you have other problems with the system—for example, a lockup (leading you to press the Reset button) or a spontaneous reboot.

You can use the following command to check filesystems...

fsck -A -V ; echo == $? ==

Note that: The purpose of the echo == $? == command is to unambiguously interpret the outcome of the fsck operation.

The outcome from this command will be one of the following.. Every outcome which is smaller than 4 is good..

0 No errors
1 Filesystem errors corrected
2 System should be rebooted
4 Filesystem errors left uncorrected
8 Operational error
16 Usage or syntax error
128 Shared library error

On the other hand; sometimes, the real problem is caused by a hardware failure. -- altough it seems like a file system error.. 

if you watch the process closely, you can catch it from server screen,  
If that is the case (San cable broken, controller error, Storage problems.. etc.) and if the root filesystem is not in the faulty disk/fault path, you can use a workaround by deleting the relevant line in the fstab file..
But in order to do that, you have to mount the root filesystem in the read write mount. This can be accomplished by the following command;

mount -o remount,rw / 

After mounting the root filesystem read/write, edit the /etc/fstab file and reboot. You will able to boot the Linux..

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