Runlevel 1 is a single-user mode, which is used for maintenance or administrative tasks. You may also see this mode referred to as runlevel S (the S stands for single-user). How to change the current runlevel? You can change the current runlevel of your system using the "telinit" command. For example, to change to runlevel 3 on CentOS, you would type: $ telinit 3 https://likegeeks.com/linux-runlevels/