In fact, it's not actually necessary to reboot in order to reach single-user mode. The init program manages the current mode, or "runlevel", for the system. The standard runlevels for a Linux system are labeled and defined as follows:

• 0: Halt the computer
• 1 or s: Single-user mode
• 2: Multi-user, no network
• 3: Multi-user, text console
• 4: Multi-user, graphical console
• 5: Same as 4
• 6: Reboot the computer

These runlevels vary between distributions, so be sure to consult your distro's documentation. To change to single-user mode, use the telinit command, which instructs init to change runlevels:

# telinit 1

You can see from the table above that you can also shutdown or reboot the system in this manner. telinit 0 will halt the computer; telinit 6 will reboot the computer. When you issue the telinit command to change runlevels, a subset of the init scripts will run to either shutdown or startup system services.