I am running Ubuntu Server, and just installed the gnome desktop on there (I neeeded to run an application that would only work in a graphical interface). However, now the server boots to the GUI every time. I need the server to boot to the command line (runlevel 3). According to several articles that I've read, Ubuntu does not use the standard runlevels. What file do I need to modify in order to boot to runlevel 3 (or whatever the Ubuntu equivalent is)?
Theoretically, if Ubuntu were compliant with UNIX and Linux standard, adding '3' to grub's 'kernel' command in /boot/grub/menu.lst should have been sufficient, because runlevel '3' means no 'X11' according to this standard.
Unfortunately, Ubuntu has ignored the standard and that's why you'll need to change /etc/init/lightdm.conf or /etc/init/gdm.conf (or whatever DM you use) as well. This is how mine "on start" condition looks like:
In Grub's menu.lst I've also added a menu item that allows me to boot to runlevel 3:
Now I can chose between booting to runlevel 5 with X11 or to runlevel 3 without it.
I think there is a good answer here (askubuntu.com)
Just to answer your question on how tho change runlevel. Edit the file /etc/init/rc-sysinit.conf and change this line.
But changing runlevel won't stop X. Look at the start condition for ligthdm:
You need change the start condition in the /etc/init/XXX file to something than isn't met, e.g. a higher runlevel than you use. XXX is the display manager you use, e.g. lightdm.conf, gdm.conf, failsafe-x.conf.
Here is deep instrtuction for runlevels - http://sysadmin.te.ua/linux/linux-boot.html
The following is for Ubuntu Server 12 LTS
First you need open a real term with CTRL+ALT F1
Stop gdm with.
$ sudo service gdm stop
Remove gdm you dont need it at all on a server.
$ sudo apt-get remove gdm
Set next boot runlevel with.
$ sudo telinit 3
Without gdm you will need to install xinit if you want to still be able to run gui based apps without the gdm window manager.
$ sudo apt-get install xinit
Reboot to runlevel 3.
$ sudo reboot
To run a GUI or desktop after reboot do.
This will start your gnome session as normal.
When finished simply logout of your desktop to and drop you back to a level 3 term
Also you can now start individual apps without a desktop too like.
$ startx nautilus
or privileged with
$ startx sudo synaptic