`sudo reboot` vs `reboot` - what is the difference?

I recently found out that reboot works just as well as sudo reboot, from what I can tell. However, in a lot of instances, I see people saying to sudo reboot. Why is this? Are they the same, and just personal preference? Or are they different? Does sudo reboot do more than reboot?

Solution 1:

On Ubuntu 14.10 and older, sudo is required.

The introduction of Systemd in 15.04 changed the way Ubuntu handles shutdown and reboot:

1. When a single user is logged in, sudo isn't necessary. When more than one user is logged in then sudo is required.

2. Applications can inhibit shutdown and reboot. You override these inhibitions with sudo.

3. A single user logged in via ssh still requires sudo.

Solution 2:

On my 14.04 machine, when I (as a normal user) type reboot, I get

reboot: Need to be root

That is the difference.

As Terrance pointed out in the comments, it works differently on later systems than mine. So you are probably seeing old writeups and/or users (like me) who have been habituated to typing sudo reboot!