This was written for Fedora, not sure how many other other distros it applies to.
There are three ways to change your runlevel:
* While the Computer is Running:
1. Open a Terminal.
2. Become root.
3. Type:
init number
where number is the runlevel that you want to change to.
You will then be switched into the new runlevel.
* While You Are Booting the Computer:
1. When you first start your computer, the GRUB screen (where you choose your Operating System) appears. Select the Fedora that you want to boot into, but press the a key instead of pressing Enter.
2. You will see a line somewhat like the following:
kernel /vmlinuz-2.6.9-1.667 ro root=LABEL=/ acpi=on rhgb quiet
Add the number of your runlevel to the end of that line, and then press Enter. For example, to boot into text-only mode, the line would look like:
kernel /vmlinuz-2.6.9-1.667 ro root=LABEL=/ acpi=on rhgb quiet 3
You will then boot into the new runlevel this time only.
* Permanently Set a Default Runlevel:
1. Open a Terminal.
2. Become root.
3. Open the file /etc/inittab in your favorite text editor:
gedit /etc/inittab
4. Find the line:
id:number:initdefault:
where number is your current default runlevel (probably 5).
5. Change the number in the middle of the line to the new runlevel that you want your computer to start in by default. For example, if you want to start in text-only mode by default, change it to:
id:3:initdefault:
You will then boot into that runlevel every time you start the computer.