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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?

Juan Sebastian Totero
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  • Are these scientific calculations dependent on a GUI program? – Marco Ceppi Jul 28 '11 at 15:54
  • @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 Jul 28 '11 at 17:20

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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.

Community
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Oli
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  • so starting X just with `startx` could create some mis-configuration problems? – Juan Sebastian Totero Jul 28 '11 at 13:58
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    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](http://www.debianadmin.com/how-to-auto-login-and-startx-without-a-display-manager-in-debian.html). Very hacky though. NoDM would be preferable in almost every possible case. – Oli Jul 28 '11 at 14:06
  • 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 ;) – Juan Sebastian Totero Jul 28 '11 at 17:22
  • 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. – Oli Jul 28 '11 at 21:45
  • 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... – Juan Sebastian Totero Jul 28 '11 at 21:58
  • I haven't read it in full but [this gives a good idea of what's going on in `xdm`](http://www.netads.com/~meo/pubsntalks/xrj/xdm.html) -- the first X display manager. – Oli Jul 28 '11 at 22:32
  • Nobody should really need NoDM anymore: [lightdm's autologin now does the right thing out of the box](https://www.enricozini.org/blog/2019/himblick/x-autologin). – karel Dec 01 '21 at 06:49