Single-user mode

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single-user mode is the first interactive runlevel for a unix/linux system in which only one user (root) is allowed access. Most daemons are not running in single-user mode and some maintenance utilities like fsck require therefore single-user mode.

Using lilo as bootmanager, you can boot linux in single-user mode by running

linux single

at the lilo: prompt of most linux distributions. This logs you on as root by default, and is very handy if you have forgotten your root password. Use passwd to reset your password in this situation.

To get into single-user mode from normal operation you may use the init command to specify the desired runlevel

init 1

When using GRUB you can append the run level number on the kernel commandline like:

kernel (hd0,0)/boot/vmlinuz-2.6.4 root=/dev/hda1 1