Tag: single user mode

Can I run fsck or e2fsck when Linux file system is mounted?

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Q. Can I run fsck or e2fsck command when Linux file system is mounted? Do you advice to run fsck on a live file system? I am using Cent OS.

A. No. Do not run fsck on a live or mounted file system. fsck is used to check and optionally repair one or more Linux file systems. Running fsck on a mounted filesystem can usually result in disk / data corruption. So please do not do it. You have two choices
(a) Take down system to single user mode and unmout system

(b) Boot from the installation CD into rescue mode

(a) Take down system to single user mode and unmout system

Following are steps :
=> Use init (process control initialization ) command to change runlevel 1 (singe user mode)
=> Use umount command to unmount /home file system
=> Run fsck using fsck command

Let us say you would like to run fsck on /home (/dev/sda3):

# init 1
# umount /home
# umount /dev/sda
# fsck /homeOR
# fsck /dev/sda3OR
# e2fsck -y /dev/sda3

(b) Boot from the installation CD into rescue mode

If you are using Cent OS/Fedora Core/RHEL linux, boot from first CD and at boot prompt type linux rescue nomount:
boot: linux rescue nomount

Now make new node for disk and partition 3:
# mknod /dev/sda
# mknod /dev/sda3
# fsck /dev/sda3
OR
# e2fsck -y /dev/sda3

Don’t forget to reboot the system:
# exit;exit
# reboot

Linux reset forgotten root password

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Q. I forgot my root password, how can I get into my system?

A. You can reset forgotten root password under Linux by booting system into single user mode or emergency mode (also known as rescue mode).

My boot loader is GRUB (see LILO boot loader below)

)Following is the procedure to reset root password if you are using GRUB as a boot loader:

  1. Select the kernel
  2. Press the e key to edit the entry
  3. Select second line (the line starting with the word kernel)
  4. Press the e key to edit kernel entry so that you can append single user mode
  5. Append the letter S (or word Single) to the end of the (kernel) line
  6. Press ENTER key
  7. Now press the b key to boot the Linux kernel into single user mode
  8. At prompt type passwd command to reset password:

You need to mount at least / and other partitions:
# mount -t proc proc /proc
# mount -o remount,rw /

Change the root password, enter:
# passwd
Finally reboot system:
# sync
# reboot

My boot loader is LILO

At LILO boot loader type linux single and press [ENTER] key:
Boot: linux single
When you get the # prompt you will need to type passwd root to reset password:
# passwd
Reboot system:
# sync
# reboot

See also: