Difference between revisions of "LXDM"

Revision as of 07:09, 29 December 2012

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Installation

Install the lxdm package which is available in the official repositories.

Usage

Currently, lxdm provides an lxdm.service file. Enable it like any other systemd service:

# systemctl enable lxdm.service

Configuration

The configuration files for LXDM are all located in /etc/lxdm. The main configuration file is lxdm.conf, and is well documented in its comments. Another file, Xsession, is the systemwide x session configuration file and should generally not be edited. The other files in this folder are all bash scripts, which are run when certain events happen in LXDM.

These are:

1. LoginReady: Is executed with root privileges when LXDM is ready to show the login window.
2. PreLogin: Is run as root before logging a user in.
3. PostLogin: Is run as the logged-in user right after they have logged in.
4. PostLogout: Is run as the logged-in user right after they have logged out.
5. PreReboot: Is run as root before rebooting with LXDM.
6. PreShutdown: Is run as root before poweroff with LXDM.

Expected Logout Behavior

What might be slightly surprising with LXDM is that, by default, it does not clear the last user's desktop background or kill the user's processes when that user logs out. Users desiring this behavior, can edit /etc/lxdm/PostLogout like this:

#!/bin/sh

# Kills all your processes when you log out.
killall --user $USER -TERM

# Sets the desktop background to solid black. Useful if you have multiple monitors.
xsetroot -solid black

Or you can replace killall command with this to exclude ssh and screen processes from termination:

ps --user $USER | egrep -v "ssh|screen" | cut -b11-15 | xargs -t kill

Default session

Globally

Edit /etc/lxdm/lxdm.conf and change the line:

session=/usr/bin/startlxde

To whatever session or DE is desired. To use xfce you would modify it to:

session=/usr/bin/startxfce4

This is useful for themes that have no visible session selection box, or if you're experiencing trouble using autologin.

Per user

To define an individual user's preferred session, simply edit his/her respective ~/.dmrc to define the selection.

Example: user1 wants xfce4, user2 wants cinnamon, and user3 wants gnome:

For user1:

[Desktop]
Session=xfce

For user2:

[Desktop]
Session=cinnamon

For user3:

[Desktop]
Session=gnome

Autologin

To log in to one account automatically, without providing a password, find the line in /etc/lxdm/lxdm.conf that looks like this:

#autologin=username

Uncomment it, then substitute your own username instead of "username".

This will cause LXDM to automatically login to the specified account when it first starts up. However, if one were to log out of that account, one would have to enter its password to log back into it; if the password was empty, that user will be unable to log into the account. To remedy this and be able to log into the account without entering a password, first delete the password:

$ passwd -d USERNAME

Then, edit the PAM file for LXDM, which is /etc/pam.d/lxdm. The files in this directory describe how users are authenticated by the various installed programs that need to do some sort of authentication. Change the line that says

auth    required    pam_unix.so

to this:

auth    required    pam_unix.so nullok

This will tell the pam_unix authentication module that blank passwords are to be accepted. After making this change, LXDM will log into accounts with blank passwords.

Unlocking Keyrings upon Login

When using a key manager such as gnome-keyring to manage passwords for ssh keys, /etc/pam.d/lxdm should be adjusted to allow users to unlock keyrings upon login if desired. The following is a functional configuration:

#%PAM-1.0
auth            requisite       pam_nologin.so
auth            required        pam_env.so
auth            required        pam_unix.so
auth            optional        pam_gnome_keyring.so
account         required        pam_unix.so
session         required        pam_limits.so
session         required        pam_unix.so
session         optional        pam_gnome_keyring.so auto_start
password        required        pam_unix.so

Sessionlist

To add/remove entries to LXDM's session dropdown menu; create/remove the .desktop files in /usr/share/xsessions as desired. A typical .desktop file will look something like:

[Desktop Entry]
Encoding=UTF-8
Name=Openbox
Comment=Log in using the Openbox window manager (without a session manager)
Exec=/usr/bin/openbox-session
TryExec=/usr/bin/openbox-session
Icon=openbox.png
Type=XSession

Simultaneous Users and Switching Users

LXDM allows multiple users to be logged into different ttys at the same time. The following command is used to allow another user to login without logging out the current user:

$ lxdm -c USER_SWITCH

Xscreensaver can also perform this task. For more, see the Xscreensaver#LXDM article.