Hello,
Am I right that Single user mode uses the least amount of system resources because it is in text and no extra processes are running.

In Ubuntu, may I know how do I automatically enable SSH Server when I use "init 1" to get into Single user mode?

Thanks.

you can't... "single user mode" does not support networking at any level. if you are looking to free up resources, you could personalise an alternative runlevel, e.g. 4 to suit your needs if you want multiple "modes" of run.

Where and how do I personalize an alternative runlevel in Ubuntu? Thanks.

Single-user mode is normally used for system maintenance tasks such as repairing filesystems and the like so I can't imagine why you'd want someone to be able to connect while you're in the middle of that, but if you really wanted to, you could switch to single-user and manually run the startup scripts until you had a configuration that had basic networking up and running. I'd guess that you'd want to go into /etc/rc.d/rc3.d (on SUSE, anyway) and run all the "K" scripts and then run the "S" scripts in order until you got networking started. (On SUSE this would be S05network.) You're definitely not going to be in single-user mode any more and you won't be quite up to level 3. At that point you could try starting the sshd daemon.

Another thing you might need to do is to make sure that /dev/pts is mounted. It's been a while but seem to recall that that needed to be mounted in order for remote logins to work. (I'd test that but I'm in the middle of testing something and don't want to risk messing it up. )

Good luck...

There is a bad idea to modify single-user mode.
Better modify any other runlevel (e.g. second) for your needs. You can do this by switching to /etc/rc2.d directory and placing the start links to /etc/init.d/networking, /etc/init.d/ssh and others needed by you daemons; and the stop links to all daemons you don't need.

Sounds like you should use runlevel 3 (in /etc/inittab) and then disable any daemons/services you don't need.