Why use a Display manager?

Question

I'm currently trying to free as much memory as possibile because I'm using my laptop for scientific simulations. One of the things I made is disable gdm and using login+startx to start GNOME session. Apart from eye-candy and comfor, is there any drawback of disabling the Display Manager? I mean, what are the reasons for the existence of GDM, KDM, LightDM and so on?

Solution

They handle pretty much everything (that isn't displaying graphics on hardware) for X. Logins, greeters, pass X the configuration for external connections, session choice.

You don't need a heavy DM but I would argue that GDM isn't that heavy. LightDM certainly isn't. But if you're really trying to hypermile things, take a look at NoDM. It's very raw and it's only intended for single-user systems. It won't provide you with any security and it might undermine what is already there.

I use NoDM on our media-centre, which just starts up X and then launches Boxee.

Comments

[Admin]

Are these scientific calculations dependent on a GUI program?

[Admin]

@Marco : Not really, in fact when I run big processes I just shut off X and everything not needed... But when I'm debugging and testing the code it's comfortable having X running :) Anyway it's not a matter of life disabling GDM, I was just curious to understand its utility :)

[Juan Sebastian Totero]

so starting X just with startx could create some mis-configuration problems?

[Oli]

It could but it's certainly possible to do that. If you don't even want NoDM (which practically does just call startx), you can hotwire tty1 to login and start X up. Very hacky though. NoDM would be preferable in almost every possible case.

[Juan Sebastian Totero]

Thanks for your replies... but the problem is that my machine is multiuser so I need in every case a login mask. Your link is anyway very iteresting ;)

[Oli]

LightDM might be worth a go. It's quite new but it's going to be in the next version of Ubuntu. There is a PPA.

[Juan Sebastian Totero]

Actually I'm trying it.... Seems nice, even if very win95ish :) I'll play with it for a while... Do you know where can I find more info about session-init operations done by gdm or any dm? Googled something but didn't find so much...

[Oli]

I haven't read it in full but this gives a good idea of what's going on in xdm -- the first X display manager.

[karel]

Nobody should really need NoDM anymore: lightdm's autologin now does the right thing out of the box.