How to stop inactive user sessions triggering Suspend to RAM in a single-seat, multi-user installation of Lubuntu 18.04

In my previous post I mentioned a problem that I had still not been able to fix in a single-seat, multi-user installation of Lubuntu 18.04: Xfce Power Manager in each user’s account can cause the installation to suspend to RAM if a user has not logged out of his/her session and another user is using a different session. Each user account in Lubuntu 18.04 has its own XfcePower Manager settings, stored in the file ~/.config/xfce4/xfconf/xfce-perchannel-xml/xfce4-power-manager.xml. If the property /xfce4-power-manager/inactivity-on-ac has a value of 15 (minutes) or higher, that session can cause the machine to suspend to RAM even if the session is not active while someone else’s session is active. The example below illustrates the effect.

Consider five users mick, christine, john, stevie and lindsey with the following settings for the number of minutes of inactivity that will trigger suspension to RAM:

mick@aspirexc600:~$ xfconf-query -c xfce4-power-manager -p /xfce4-power-manager/inactivity-on-ac
30

christine@aspirexc600:~$ xfconf-query -c xfce4-power-manager -p /xfce4-power-manager/inactivity-on-ac
25

john@aspirexc600:~$ xfconf-query -c xfce4-power-manager -p /xfce4-power-manager/inactivity-on-ac
45

stevie@aspirexc600:~$ xfconf-query -c xfce4-power-manager -p /xfce4-power-manager/inactivity-on-ac
15

lindsey@aspirexc600:~$ xfconf-query -c xfce4-power-manager -p /xfce4-power-manager/inactivity-on-ac
30

Now, suppose that john boots the machine, logs in to his account to check his e-mail, leaves the e-mail client open and goes off to grab lunch without logging out. Then stevie comes along and clicks on ‘Logout’ > ‘Switch User’ to display the LightDM greeter screen (or the greeter screen is already displayed because john‘s session has already been locked), logs in to her account and begins to use, say, LibreOffice Writer. Even though stevie is busy typing, the machine will suspend to RAM after 45 minutes of inactivity by john. This can be very annoying.

In addition to the individual users’ Xfce Power Manager configuration files in Lubuntu 18.04, I found the following Xfce Power Manager configuration files which appear to be system-wide:

/etc/xdg/xdg-Lubuntu/xfce4/xfconf/xfce-perchannel-xml/xfce4-power-manager.xml
/etc/xdg/xfce4/xfconf/xfce-perchannel-xml/xfce4-power-manager.xml

First attempt at fixing the problem

I asked all the users to configure their accounts to never cause the machine to suspend, by using the Xfce Power Manager settings GUI in their session and selecting ‘Never’. I noticed this caused each user’s /xfce4-power-manager/inactivity-on-ac property to become ‘14‘:

user $ xfconf-query -c xfce4-power-manager -p /xfce4-power-manager/inactivity-on-ac
14

Note that users must not edit their file ~/.config/xfce4/xfconf/xfce-perchannel-xml/xfce4-power-manager.xml; if they do, the settings shown in the Xfce Power Manager settings GUI will not be updated. Users must either use the Xfce Power Manager settings GUI or xfconf-query commands as explained on the askubuntu Web page ‘Change xfce4-power-manager option from terminal‘.

Then I edited the file /etc/xdg/xdg-Lubuntu/xfce4/xfconf/xfce-perchannel-xml/xfce4-power-manager.xml to make its contents the same as the previous contents of the individual users’ settings when Suspend to RAM was enabled individually):

<?xml version="1.0" encoding="UTF-8"?>

<channel name="xfce4-power-manager" version="1.0">
  <property name="xfce4-power-manager" type="empty">
    <property name="power-button-action" type="uint" value="3"/>
    <property name="show-tray-icon" type="bool" value="true"/>
    <property name="brightness-switch-restore-on-exit" type="int" value="1"/>
    <property name="brightness-switch" type="int" value="0"/>
    <property name="presentation-mode" type="bool" value="false"/>
    <property name="inactivity-on-ac" type="uint" value="30"/>
    <property name="blank-on-ac" type="int" value="10"/>
    <property name="dpms-on-ac-sleep" type="uint" value="0"/>
    <property name="dpms-on-ac-off" type="uint" value="0"/>
    <property name="brightness-on-ac" type="uint" value="9"/>
    <property name="lock-screen-suspend-hibernate" type="bool" value="true"/>
    <property name="logind-handle-lid-switch" type="bool" value="false"/>
    <property name="dpms-enabled" type="bool" value="false"/>
    <property name="general-notification" type="bool" value="true"/>
    <property name="sleep-button-action" type="uint" value="0"/>
    <property name="hibernate-button-action" type="uint" value="0"/>
  </property>
</channel>

After rebooting, leaving one or more users logged in without any activity did not cause the installation to suspend to RAM after 30 minutes of no activity in any session.

So I then edited the file /etc/xdg/xfce4/xfconf/xfce-perchannel-xml/xfce4-power-manager.xml to make its contents the same as the above. After rebooting, leaving one or more users logged in without any activity did not cause the installation to suspend to RAM after 30 minutes of no activity in any session.

I therefore assume that the above two files are ignored by Xfce Power Manager during normal operation.

Second attempt at fixing the problem

I used the procedure given in the Xfce4-power-manager FAQs to check if Xfce Power Manager in Lubuntu 18.04 uses systemd-logind to suspend the installation, and indeed it does:

TRACE[xfpm-polkit.c:366] xfpm_polkit_check_auth_intern(): Action=org.freedesktop.login1.suspend is authorized=TRUE

Therefore I edited /etc/systemd/logind.conf to add IdleAction=suspend and IdleActionSec=30min, and rebooted. However, this had no discernable effect either. Leaving one or more users logged in without any activity did not cause the installation to suspend to RAM after 30 minutes of no activity in any session.

Third attempt (successful) at fixing the problem

So, what to do?! In my previous post I explained how I had fixed the problem of not being able to suspend to RAM automatically from the LightDM greeter screen. I decided to keep the scripts from that post and add a new script sessions_sleep.sh to the root crontab. The contents of all the files and the crontab are shown below.

user $ cd /etc/lightdm/lightdm.conf.d/
user $ cat 10_lubuntu.conf 
[Seat:*]
greeter-setup-script=/etc/lightdm/lightdm.conf.d/lightdm_sleep.sh
session-setup-script=/etc/lightdm/lightdm.conf.d/lightdm_kill_sleep.sh
session-cleanup-script=/etc/lightdm/lightdm.conf.d/unmount_FREECOM_HDD.sh

user $ ls
05_lubuntu.conf  lightdm_kill_sleep.sh       sessions_sleep.sh
10_lubuntu.conf  lightdm_sleep.sh            unmount_FREECOM_HDD.sh

user $ cat lightdm_sleep.sh 
#!/bin/bash
# This forms part of the scheme to provide automatic suspension while the greeter screen is displayed
file="/tmp/unique_identifier"
(while true; do sleep 30m; systemctl suspend; done) &
echo $! > $file

user $ cat lightdm_kill_sleep.sh
#!/bin/bash
# This forms part of the scheme to provide automatic suspension while the greeter screen is displayed
file="/tmp/unique_identifier"
if [ -f "$file" ]; then
    kill `cat $file`
    rm $file
fi

user $ tail -n 11 unmount_FREECOM_HDD.sh
#----------------------------------------------------------------------------------------------------
#
# This forms part of the scheme to provide automatic suspension while the greeter screen is displayed
file="/tmp/unique_identifier"
if [ -f "$file" ]; then
    kill `cat $file`
    rm $file
fi
#
#----------------------------------------------------------------------------------------------------
exit 0

If the machine did not already have a permanently-connected external USB HDD (LABEL=”FREECOM HDD”) then it would have sufficed to specify a script named, for example, lightdm_kill_sleep2.sh instead of unmount_FREECOM_HDD.sh:

user $ cat 10_lubuntu.conf 
[Seat:*]
greeter-setup-script=/etc/lightdm/lightdm.conf.d/lightdm_sleep.sh
session-setup-script=/etc/lightdm/lightdm.conf.d/lightdm_kill_sleep.sh
session-cleanup-script=/etc/lightdm/lightdm.conf.d/lightdm_kill_sleep2.sh
user $ cat lightdm_kill_sleep2.sh
#!/bin/bash
# This forms part of the scheme to provide automatic suspension while the greeter screen is displayed
file="/tmp/unique_identifier"
if [ -f "$file" ]; then
    kill `cat $file`
    rm $file
fi

user $ sudo nano sessions_sleep.sh
user $ sudo chmod +x sessions_sleep.sh
user $ cat sessions_sleep.sh 
#!/bin/bash
date +%s > /tmp/datetime_suspended # Initialise variable
while true
do
    # Only monitor idle time and suspend after specified inactivity if lightdm_sleep.sh is not taking care of those
    if [[ `ps -ef | grep bash | grep lightdm_sleep.sh | wc -l` -eq 0 ]]; then
        #-------------------------------STAGE 1: FIND OUT WHO IS THE ACTIVE USER--------------------------------------
        #
        while IFS=: read -r f1 f2 f3 f4 f5 f6 f7
        # $f1 is username
        # $f2 is password ('x')
        # $f3 is UID
        # $f4 is GID
        # $f5 is UID info
        # $f6 is home directory
        # $f7 is command/shell
        do
            if [[ $f6 == *"/home/"* ]] && [[ $f7 == "/bin/bash" ]]; then
                if `loginctl list-users | grep -ve '^$\|USER\|listed' | awk -F' ' '{print $2}' | grep -q $f1`; then
                    state=`loginctl show-user $f3 | grep State | awk -F'=' '{print $2}'`
                    if [[ $state != "active" ]]; then
                        inactive_user=$f1
                    elif [[ $state == "active" ]]; then
                        active_user=$f1
                    fi
                fi
            fi
        done < /etc/passwd
        #
        #-------------------------------STAGE 2: ASCERTAIN USER SESSIONS---------------------------------------------
        #
        # Find idle time for each X Windows session and suspend to RAM if the active user has been idle for >=30min.
        #
        who -u | grep -v "\." > /tmp/logged-in_users
        #
        while read a b c d e f g
        # $a is username
        # $b is the tty (tty1 to tty12)
        # $c is the date (yyyy-mm-dd)
        # $d is the time (hh:mm)
        # $e is the idle time (hh:mm) which does not reflect reality in this installation, for some reason
        # $f is the PID
        # $g is the display e.g. "(:1)"
        # Example: "john     tty7         2019-08-31 17:08 00:01        1624 (:0)"
        do
            if [[ $(echo $b | sed 's/[^0-9]*//g') -gt 6 ]]; then
                display=$(echo $g | sed 's/[^0-9]*//g')
                idle_millisecs=$(env DISPLAY=:$display sudo -u $a xprintidle)
                let idle_minutes=$idle_millisecs/60000
                if [[ $idle_minutes -ge 30 ]] && [[ $a == "$active_user" ]]; then
                    datetime_now=$(date +%s)
                    diffsecs=$(expr $datetime_now - $(cat /tmp/datetime_suspended))
                    # Prevent suspending immediately after resuming
                    if [ $diffsecs -gt 180 ]; then
                        date +%s > /tmp/datetime_suspended
                        systemctl suspend
                    fi
                fi
            fi
        done < /tmp/logged-in_users
        rm /tmp/logged-in_users
        #
        #------------------------------------------------------------------------------------------------------------
        sleep 10 # Frequency to repeat check
    fi
done

I installed the utility xprintidle via the Linux distribution’s package manager. As the name of the utility suggests, it returns the time (in milliseconds) that an X Windows session has been idle. Nice utility, by the way.

user $ sudo crontab -e
user $ sudo crontab -l | grep -v ^#
@reboot sudo /etc/lightdm/lightdm.conf.d/sessions_sleep.sh

Note that, despite its name, ‘@reboot‘ in the cron job will run the script after a cold boot as well as after a warm boot (reboot). Also note that the use of ‘sudo‘ in the root cron job is not an error; it makes the root cron job use the root user’s environment variables.

Remember that the property /xfce4-power-manager/inactivity-on-ac has to be configured to have a value of 14 (which corresponds to ‘Never’ in the Xfce Power Manager settings GUI) for every user. This should be done by each user using the Xfce Power Manager settings GUI in their own session.

Basically, the scheme works as follows: At boot, Lubuntu 18.04 launches the looping Bash script sessions_sleep.sh, which remains running but does nothing because no X Windows users are logged in. When LightDM runs the greeter-setup-script (lightdm_sleep.sh) and displays the greeter screen, sessions_sleep.sh still does nothing while lightdm_sleep.sh is running and taking care of managing suspension. When an X Windows user logs in and LightDM’s session-setup-script (lightdm_kill_sleep.sh) kills the running script lightdm_sleep.sh, the script sessions_sleep.sh then takes over monitoring users’ activity in X Windows and triggers suspension if the active user has not used his/her session for 30 minutes. If an X Windows user logs out, LightDM’s session-cleanup-script (unmount_FREECOM_HDD.sh) also kills lightdm_sleep.sh if it is running. When LightDM again runs its greeter-setup-script (lightdm_sleep.sh) and displays the greeter screen, that again inhibits sessions_sleep.sh from taking any action if no X Windows user is logged in. This all sounds convoluted, but it seems to work fine so far.

Because Xfce Power Manager is no longer used to monitor idle time and trigger suspension, ‘Presentation mode’ in Xfce Power Manager can no longer prevent the system from suspending after 30 minutes of inactivity while someone is watching a long video or playing music, for example. However this is not a problem; to temporarily inhibit suspension the user can use the method given in my earlier post ‘How to move a mouse pointer automatically in Linux to simulate user activity‘.

The Lubuntu 18.04 architecture

I suspect most Lubuntu 18.04 installations are on laptops or desktop machines with a single user, i.e. single-seat, single-user installations. In such a case, unless the user has created multiple user accounts that he/she logs into concurrently (by using ‘Switch User’, for example), the machine will never suspend unexpectedly while the user is logged in and using the session. I think the way LightDM, light-locker, systemd-logind and Xfce Power Manager have been bundled in Lubuntu 18.04 to manage suspending to RAM is a dog’s breakfast. The design apparently does not take into consideration that different people could be logged in concurrently in a single-seat installation. Try forcing people to log off so that only one person is ever logged in — it won’t happen! To be interrupted by Suspend to RAM triggered by Xfce Power Manager due to inactivity in a different session is illogical; the system should not suspend when someone is actively using the system. Therefore, in my opinion, management of suspension (and hibernation) ought to be configured and managed system-wide, not on a per-user basis, and a design should not require users to hack the installation to the extent I have described above. I was ‘scratching an itch’, but users should not have to jump through hoops to get an installation to function in a sensible manner. For all I know there may be a simpler way of achieving the functionality in Lubuntu 18.04 that I have described in this post and my previous post, but, if there is, it is not obvious. LightDM, light-locker, systemd and Xfce Power Manager are developed by different people, and functionality such as suspension and hibernation does not seem to have been considered using ‘helicopter vision’. Designing disparate applications developed separately to work together holistically is not a trivial task.

Anyway, hopefully I have fixed the problem and also ‘scratched my itch’. No more unexpected suspensions while I am using the family desktop machine!

How to make LightDM suspend to RAM automatically from the login screen and lock screen in Lubuntu 18.04

My family’s desktop machine has Lubuntu 18.04 installed, which generally works well. Each family member has their own account, therefore the installation is a single-seat, multi-user system. Lubuntu 18.04 uses LightDM for the display manager, light-locker (which uses LightDM) for the screen locker, and Xfce Power Manager for power management. Xfce Power Manager enables each user to specify for their session that the machine will suspend to RAM, and to configure the duration of inactivity in their session that will trigger suspension.

However, a couple of things about this arrangement are annoying. Firstly, if two or more users happen to be logged-in simultaneously because a family member does not bother to log out, Xfce Power Manager in an inactive session will eventually suspend the machine even when another user is actively using a different session. Secondly, if nobody is logged-in and the LightDM greeter screen is displayed, the machine will not suspend to RAM automatically after a period of inactivity. The only way to get the machine to suspend to RAM if nobody is logged-in is to click on the power indicator in the greeter’s system tray and select ‘Suspend’ from the drop-down menu.

I still have not figured out how to fix the first of the above-mentioned problems, but a Web search finally turned up a fix for the second problem: a post by Linux user boyi in Arch Linux Forums thread ‘need lightdm to suspend system‘. Below I explain how I implemented this in my family’s Lubuntu 18.04 installation. Basically, when the LightDM greeter screen is displayed LightDM runs a looping shell script (lightdm_sleep.sh) that will suspend the machine after a specified time has elapsed, and either logging in or unlocking the screen will run another shell script (lightdm_kill_sleep.sh) that kills the first script. Once a user has either logged in or unlocked the screen, Xfce Power Manager in that user’s session takes over monitoring activity.

1. Pre-existing situation
When I originally installed Lubuntu 18.04 I made sure each user used the Xfce Power Manager GUI to configure suspension to RAM. Each user’s own settings are shown below:

user $ cat ~/.config/xfce4/xfconf/xfce-perchannel-xml/xfce4-power-manager.xml
<?xml version="1.0" encoding="UTF-8"?>

<channel name="xfce4-power-manager" version="1.0">
  <property name="xfce4-power-manager" type="empty">
    <property name="power-button-action" type="uint" value="3"/>
    <property name="show-tray-icon" type="bool" value="true"/>
    <property name="brightness-switch-restore-on-exit" type="int" value="1"/>
    <property name="brightness-switch" type="int" value="0"/>
    <property name="presentation-mode" type="bool" value="false"/>
    <property name="inactivity-on-ac" type="uint" value="30"/>
    <property name="blank-on-ac" type="int" value="10"/>
    <property name="dpms-on-ac-sleep" type="uint" value="0"/>
    <property name="dpms-on-ac-off" type="uint" value="0"/>
    <property name="brightness-on-ac" type="uint" value="9"/>
    <property name="lock-screen-suspend-hibernate" type="bool" value="true"/>
    <property name="logind-handle-lid-switch" type="bool" value="false"/>
    <property name="dpms-enabled" type="bool" value="false"/>
    <property name="general-notification" type="bool" value="true"/>
    <property name="sleep-button-action" type="uint" value="3"/>
    <property name="hibernate-button-action" type="uint" value="3"/>
  </property>
</channel>

Note that each user must not edit their file ~/.config/xfce4/xfconf/xfce-perchannel-xml/xfce4-power-manager.xml directly, as the properties in the Xfce Power Manager settings GUI will not be updated if they do. Users must either use the Xfce Power Manager settings GUI or use xfconf-query commands on the command line as explained on the askubuntu Web page ‘Change xfce4-power-manager option from terminal‘.

The LightDM configuration files in /etc/lightdm/lightdm.conf.d/ were as follows:

user $ ls /etc/lightdm/lightdm.conf.d/
05_lubuntu.conf  10_lubuntu.conf  unmount_FREECOM_HDD.sh

The file 05_lubuntu.conf was installed when I installed Lubuntu 18.04. The two files 10_lubuntu.conf and unmount_FREECOM_HDD.sh were previously created by me in order to unmount a permanently-connected external USB HDD when a user logs out, to avoid an access problem when another user logs in (see an earlier blog post).

user $ cat /etc/lightdm/lightdm.conf.d/10_lubuntu.conf
[Seat:*]
session-cleanup-script=/etc/lightdm/lightdm.conf.d/unmount_FREECOM_HDD.sh

2. Modifications to enable installation to suspend when no user is logged in

2.1 Specify the scripts

user $ cd /etc/lightdm/lightdm.conf.d/
user $ sudo nano 10_lubuntu.conf
user $ cat 10_lubuntu.conf 
[Seat:*]
greeter-setup-script =/etc/lightdm/lightdm.conf.d/lightdm_sleep.sh
session-setup-script=/etc/lightdm/lightdm.conf.d/lightdm_kill_sleep.sh
session-cleanup-script=/etc/lightdm/lightdm.conf.d/unmount_FREECOM_HDD.sh

2.2 Create the two scripts

user $ sudo nano lightdm_sleep.sh
user $ sudo chmod +x lightdm_sleep.sh
user $ cat lightdm_sleep.sh 
#!/bin/sh
file="/tmp/unique_identifier"
(while true; do sleep 30m; systemctl suspend; done) &
echo $! > $file

user $ sudo nano lightdm_kill_sleep.sh
user $ sudo chmod +x lightdm_kill_sleep.sh
user $ cat lightdm_kill_sleep.sh 
#!/bin/sh
file="/tmp/unique_identifier"
if [ -f "$file" ]
then
    kill `cat $file`
    rm $file
fi

2.3 Modify the existing session cleanup script to include the lightdm_kill_sleep.sh code

user $ tail -n 11 unmount_FREECOM_HDD.sh
################################################
# Code below copied from lightdm_kill_sleep.sh
file="/tmp/unique_identifier"
if [ -f "$file" ]
then
    kill `cat $file`
    rm $file
fi
# End of code copied from lightdm_kill_sleep.sh
################################################
exit 0

Of course, specifying lightdm_kill_sleep.sh would have sufficed if the installation did not already have a session cleanup script:

user $ cat 10_lubuntu.conf
[Seat:*]
greeter-setup-script =/etc/lightdm/lightdm.conf.d/lightdm_sleep.sh
session-setup-script=/etc/lightdm/lightdm.conf.d/lightdm_kill_sleep.sh
session-cleanup-script=/etc/lightdm/lightdm.conf.d/lightdm_kill_sleep.sh

3. Summary
Thus the file situation is now as follows:

user $ ls /etc/lightdm/lightdm.conf.d/
05_lubuntu.conf  10_lubuntu.conf  lightdm_kill_sleep.sh  lightdm_sleep.sh  unmount_FREECOM_HDD.sh

• If nobody logs in after booting the machine, the machine will suspend to RAM after 30 minutes* due to greeter-setup-script.
• If a user logs in, session-setup-script ensures only Xfce Power Manager controls suspension to RAM while the LightDM greeter screen is not displayed.
• If a user logs out and no other user is logged in, the machine will suspend to RAM after 30 minutes* due to greeter-setup-script.
• If a user locks the screen, the machine will suspend to RAM after 30 minutes* due to greeter-setup-script.

*Obviously the period of inactivity to trigger suspension to RAM can be configured by changing the time specified in the lightdm_sleep.sh script.

How to display a user’s avatar instead of the generic avatar on the LightDM GTK Greeter screen in Lubuntu 17.10

I recently installed Lubuntu 17.10 on my family’s PC (single-seat, multi-user). The default avatar was displayed for each user on the LightDM greeter screen, rather than each user’s individual avatar. I have experienced this problem in more than one Linux distribution (Gentoo, Sabayon and now Lubuntu 17.10), more than one Desktop Environment (KDE, GNOME and now LXDE), and more than one Display Manager (LightDM and SDDM), so my suspicion is that the problem lies with AccountsService rather than the DE or DM. Anyway, here is how I fixed the problem in Lubuntu 17.10. The example below is for user fitzcarraldo, and I used the same procedure for each username in the installation.

1. Create a 96×96 PNG avatar /home/fitzcarraldo/Pictures/fitzcarraldo.png

2. Edit the file /var/lib/AccountsService/users/fitzcarraldo to contain the following:

[User]
XSession=Lubuntu
SystemAccount=false
Icon=/var/lib/AccountsService/icons/fitzcarraldo	

3. Make sure that the file has 644 permissions:

$ ls -la /var/lib/AccountsService/users/fitzcarraldo
-rw-r--r-- 1 root root 85 Jan  1 02:53 /var/lib/AccountsService/users/fitzcarraldo

4. Copy the avatar to the relevant directory and make sure it has 644 permissions:

$ sudo cp /home/fitzcarraldo/Pictures/fitzcarraldo.png /var/lib/AccountsService/icons/fitzcarraldo
$ ls -la /var/lib/AccountsService/icons/fitzcarraldo
-rw-r--r-- 1 root root 14860 Jan  1 02:54 /var/lib/AccountsService/icons/fitzcarraldo

After rebooting, the desired avatar should be displayed on LightDM’s GTK Greeter screen.

Background reading

1. KDE Bug Report No. 336994 – User Manager does not show one particular user in the list unless I login as that user
2. Gentoo Forums – user-manager in plasma desktop not populating users
3. Gentoo Forums – LightDM greeter username in list stuck and can’t add others

How to capture a screenshot of the LightDM greeter screen

1. If they are not already installed, install the packages x11-apps/xwd and media-gfx/imagemagick.
   

2. Create the Bash script ~/lightdm-greeter-capture.sh containing the following:

   #!/bin/bash
   sleep 30
   DISPLAY=:0 XAUTHORITY=/var/run/lightdm/root/$DISPLAY xwd -root > /tmp/greeter.xwd
   convert /tmp/greeter.xwd /home/fitzcarraldo/greeter.png
   

   Make sure you make it executable:

   user $ chmod +x lightdm-greeter-capture.sh

3. Log out of the Desktop Environment so that the LightDM greeter screen is displayed.
   

4. Press Ctrl+Alt+F2 to switch to VT2.
   

5. Log in to you user account and enter the following command (do not wait for it to complete):
   

   user $ sudo /home/fitzcarraldo/lightdm-greeter-capture.sh

6. As soon as you have pressed Enter for the above command, press Ctrl+Alt+F7 to switch back to VT7.
   

7. Wait for at least 30 seconds to be sure the Bash script has made a snapshot of the LightDM greeter screen, then log in.
   

8. You should now find the file ~/greeter.png containing a snapshot of your LightDM greeter screen.

If you install media-libs/netpbm instead of (or as well as) media-gfx/imagemagick then you can use a different command to convert in the Bash script:

#!/bin/bash
sleep 30
DISPLAY=:0 XAUTHORITY=/var/run/lightdm/root/$DISPLAY xwd -root | xwdtopnm | pnmtopng > /home/fitzcarraldo/greeter.png

The resulting PNG image looks equally good to my eyes.

Fixing all-white log-in screen when using the LightDM KDE greeter with Plasma 5 in Gentoo Linux

In a previous post I explained how I got LightDM to work on my Clevo W230SS laptop running KDE Plasma 5 in Gentoo Linux (Stable Branch). However, following a world update a few weeks later, the LightDM log-in screen (‘greeter’) became all white. Searching the Web showed me that this is a common problem with LightDM, although the cause appeared to be different in many other cases, as I could still see the password-entry box and the button to select the session.

To summarise what was already installed:

fitzcarraldo@clevow230ss ~ $ uname -a
Linux clevow230ss 3.18.11-gentoo #47 SMP Thu May 26 11:03:29 BST 2016 x86_64 Intel(R) Core(TM) i7-4810MQ CPU @ 2.80GHz GenuineIntel GNU/Linux
fitzcarraldo@clevow230ss ~ $ eix -I plasma-meta
[I] kde-plasma/plasma-meta
     Available versions:  (5) 5.6.5 ~5.7.3
       {bluetooth +display-manager grub gtk +handbook mediacenter networkmanager pam plymouth pulseaudio +sddm sdk +wallpapers}
     Installed versions:  5.6.5(5)(12:28:08 26/07/16)(bluetooth display-manager gtk handbook networkmanager pam pulseaudio wallpapers -grub -mediacenter -plymouth -sddm -sdk)
     Homepage:            https://www.kde.org/workspaces/plasmadesktop/
     Description:         Merge this to pull in all Plasma 5 packages

fitzcarraldo@clevow230ss ~ $ eix -I lightdm
[I] x11-misc/lightdm
     Available versions:  1.10.5^t 1.16.7^t ~1.17.6^t ~1.18.1^t ~1.19.0^t ~1.19.3^t {audit +gnome +gtk +introspection kde qt4 qt5}
     Installed versions:  1.16.7^t(04:11:41 23/08/16)(introspection kde qt4 qt5 -audit -gnome -gtk)
     Homepage:            https://www.freedesktop.org/wiki/Software/LightDM
     Description:         A lightweight display manager

[I] x11-misc/lightdm-kde
     Available versions:  (4) 0.3.2.1-r1
       {aqua debug L10N="bs cs da de el es et fi fr ga gl hu it ja km lt mr nds nl pl pt pt-BR ro ru sk sl sv tr uk"}
     Installed versions:  0.3.2.1-r1(4)(01:13:13 12/07/16)(-aqua -debug L10N="pt-BR -bs -cs -da -de -el -es -et -fi -fr -ga -gl -hu -it -ja -km -lt -mr -nds -nl -pl -pt -ro -ru -sk -sl -sv -tr -uk")
     Homepage:            https://projects.kde.org/projects/playground/base/lightdm
     Description:         LightDM KDE greeter

Found 2 matches

And this is what I had previously configured:

fitzcarraldo@clevow230ss ~ $ grep -v ^# /etc/lightdm/lightdm.conf
[LightDM]

session-wrapper=/etc/lightdm/Xsession
[Seat:*]
greeter-session=lightdm-kde-greeter
session-wrapper=/etc/lightdm/Xsession
display-setup-script=/etc/X11/Sessions/plasma

[XDMCPServer]

[VNCServer]
fitzcarraldo@clevow230ss ~ $ cat /etc/X11/Sessions/plasma
#!/bin/bash
GPU=`eselect opengl list | grep \* | awk '{ print $2 }'`
if [ "$GPU" = "nvidia" ]; then
    xrandr --setprovideroutputsource modesetting NVIDIA-0
    xrandr --auto
fi

Now, given that I had installed the LightDM KDE Greeter, I would have expected there to be a default configuration file lightdm-kde-greeter.conf for it, but there was none:

fitzcarraldo@clevow230ss ~ $ ls /etc/lightdm/
Xsession  keys.conf  lightdm.conf  users.conf

So I created the file /etc/lightdm/lightdm-kde-greeter.conf with the following contents:

[greeter]
theme-name=classic

[greeter-settings]
Background=/home/fitzcarraldo/Pictures/Wallpaper/Linux/kde-1920x1080.jpg
BackgroundKeepAspectRatio=true
GreetMessage=Welcome to %hostname%

I downloaded a nice KDE wallpaper file from the Web, which I saved as /home/fitzcarraldo/Pictures/Wallpaper/Linux/kde-1920x1080.jpg, but you can save it anywhere you like and give it any name you want.

I found that the package manager had installed two themes, so I could have specified either:

fitzcarraldo@clevow230ss ~ $ ls /usr/share/apps/lightdm-kde-greeter/themes/
classic  userbar

Anyway, the outcome is that the LightDM login screen (greeter) is no longer white and displays a wallpaper of my choice. Mission accomplished.