Ubuntu – How to change user from command line

Install acpi and acpi-support, if not already installed.

• Go to /etc/acpi/events.
• There should be a file named powerbtn (if not, make it). The contents of the file in my installation are:

# /etc/acpi/events/powerbtn
# This is called when the user presses the power button and calls
# /etc/acpi/powerbtn.sh for further processing.

# Optionally you can specify the placeholder %e. It will pass
# through the whole kernel event message to the program you've
# specified.

# We need to react on "button power.*" and "button/power.*" because
# of kernel changes.

event=button[ /]power
action=/etc/acpi/powerbtn.sh

• You can associate an action with the powerbutton by editing the action variable in this file.
• In my installation, the contents of /etc/acpi/powerbtn.sh are:

#!/bin/sh
# /etc/acpi/powerbtn.sh
# Initiates a shutdown when the power putton has been
# pressed.

[ -r /usr/share/acpi-support/power-funcs ] && . /usr/share/acpi-support/power-funcs

# getXuser gets the X user belonging to the display in $displaynum.
# If you want the foreground X user, use getXconsole!
getXuser() {
        user=`pinky -fw | awk '{ if ($2 == ":'$displaynum'" || $(NF) == ":'$displaynum'" ) { print $1; exit; } }'`
        if [ x"$user" = x"" ]; then
                startx=`pgrep -n startx`
                if [ x"$startx" != x"" ]; then
                        user=`ps -o user --no-headers $startx`
                fi
        fi
        if [ x"$user" != x"" ]; then
                userhome=`getent passwd $user | cut -d: -f6`
                export XAUTHORITY=$userhome/.Xauthority
        else
                export XAUTHORITY=""
        fi
        export XUSER=$user
}

# Skip if we just in the middle of resuming.
test -f /var/lock/acpisleep && exit 0

# If the current X console user is running a power management daemon that
# handles suspend/resume requests, let them handle policy This is effectively
# the same as 'acpi-support's '/usr/share/acpi-support/policy-funcs' file.

[ -r /usr/share/acpi-support/power-funcs ] && getXconsole
PMS="gnome-settings-daemon kpowersave xfce4-power-manager"
PMS="$PMS guidance-power-manager.py dalston-power-applet"

if pidof x $PMS > /dev/null; then
        exit
elif test "$XUSER" != "" && pidof dcopserver > /dev/null && test -x /usr/bin/dcop && /usr/bin/dcop --user $XUSER kded kded loadedModules | grep -q klaptopdaemon; then
        exit
elif test "$XUSER" != "" && test -x /usr/bin/qdbus; then
        kded4pid=$(pgrep -n -u $XUSER kded4)
        if test "$kded4pid" != ""; then
                dbusaddr=$(su - $XUSER -c "grep -z DBUS_SESSION_BUS_ADDRESS /proc/$kded4pid/environ")
                if test "$dbusaddr" != "" && su - $XUSER -c "export $dbusaddr; qdbus org.kde.kded" | grep -q powerdevil; then
                        exit
                fi
        fi
fi

# If all else failed, just initiate a plain shutdown.
/sbin/shutdown -h now "Power button pressed"

Try this. Edit /etc/acpi/powerbtn.sh, and the make sure that the lines below are the last lines in it.

# If all else failed, just initiate a plain shutdown.
/sbin/shutdown -h now "Power button pressed"

also look in /etc/acpi/events/powerbtn, and make sure it matches below, specially the last part.

# /etc/acpi/events/powerbtn
# This is called when the user presses the power button and calls
# /etc/acpi/powerbtn.sh for further processing.

# Optionally you can specify the placeholder %e. It will pass
# through the whole kernel event message to the program you've
# specified.

# We need to react on "button power.*" and "button/power.*" because
# of kernel changes.

event=button[ /]power
action=/etc/acpi/powerbtn.sh

If you make any changes, make sure you run, before you try to see if it works. You may need to reboot.

sudo service acpid restart