Question: I know how to boot into single user mode under Linux and FreeBSD. But, how do I boot into single user mode under HP-UX (HP9000) UNIX operating system?
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Q. How do I fix the following error under CentOS Enterprise Linux:

LVM error VG meta data inconsistent

How do I fix this problem?

A. You need to use lvm command, which provides the command-line tools for LVM2. In order to fix this problem boot your Linux into rescue mode or a single user mode:

First, you need to restore the VG Meta data, enter:
lvm vgcfgrestore VG

Now, you need to rescan for physical devices and vol groups (scan all disks for physical volume), enter:
lvm pvscan
lvm vgscan

Finally, make the volume group active, enter:
lvm vgchange -ay VG

For more information read lvm man page:
man lvm

Q. I’m using CentOS Linux 5 server with ext3 on /disk2 (/dev/sdb1). How do I improve my file server performance. I’ve many large files in directories and how do I speed up access time?
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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

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:

• Howto: Recovering grub boot loader password
• Recovering deleted /etc/shadow password file
• 10 boot time parameters you should know about the Linux kernel
• Debian Linux – Grub Boot into single user mode

Q. How do I boot a Linux system into single user mode?
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