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Hibernation

Hibernation (also known as suspend-to-disk) is a method used to power down a computer while preserving the state of the operating system. Once powered up, the operating system will be in the exact state as it was at the time of hibernation.

In Slackware, hibernation works out-of-the-box. However, in order to resume successfully from a hibernated state, you need to configure the bootloader so it knows where to locate the resume data.

Hibernating

Desktop Environments

KDE, XFCE and other desktop environments offer hibernation from logout screen/menu.

Lightweight Window Managers

You can hibernate your system from console. Either as root via pm-utils or D-Bus with additional programs as regular user.

pm-utils

Hibernation is done via pm-hibernate command.

D-Bus

Slackware offers two services to control power management in it's recent releases. UPower and HAL. Since HAL is deprecated in Slackware 14.0, use HAL in older Slackware releases (from 12.0 to 13.37), otherwise use UPower.

Use one of these command to hibernate your system.

UPower
 $ dbus-send --system --print-reply --dest="org.freedesktop.UPower" \
 /org/freedesktop/UPower org.freedesktop.UPower.Hibernate
HAL
$ dbus-send --system --print-reply --dest="org.freedesktop.Hal" \
 /org/freedesktop/Hal/devices/computer org.freedesktop.Hal.Device.SystemPowerManagement.Hibernate

Bootloader configuration

Booting from LVM

LILO doesn't support booting from LVM, therefore you have to create initial ramdisk (initrd). You need one even though your kernel has build-in support for LVM.

You don't have to specially adjust lilo.conf because you can set everything resume-related in initrd.

mkinitrd -c -k <kernel-version> -f <fs_type> -m <modules_required_to_boot> -r <root_partition> -h /dev/volumegroup/swap -L
  • -h set your hibernation/swap logical volume
  • -L activate LVM

LILO configuration

Next step is to make sure your lilo.conf contains following snippet

image = /boot/vmlinuz
  root = /dev/sdaX
  initrd = /boot/initrd.gz
  label = Slackware
  read-only # Partitions should be mounted read-only

If you don't use LVM, you can simply tell kernel where to resume from by adding append line:

append="resume=/dev/sdaX"

Replace /dev/sdaX with your actual swap partition.

Afterwards, run lilo to save changes.

$ lilo

Lock your computer upon resuming

You may have noticed that when your computer resumes, there is no protection to ensure no one can use your computer. As pm-hibernate must be run as root, any user that powers up your computer will be granted a root terminal! I'll show you some tricks to ensure a proper lock of the system.

Security warning: whether you are using the trick from the command-line or from an X session, don't forget to logout from all other ttys! None of them will get locked, so people issuing CTRL+ALT+F1 (ar any Fx key) upon resuming will be able to access them, rendering the lock trick totally useless!

With pm-utils

From the command line

If you dont have an X session open, the only way to lock your computer is to logout from your session before hibernation. You can use the following command:

pm-hibernate & logout (OR pm-hibernate & exit)

It's important to logout from every tty prior to hibernation! logout will only log you out from the terminal from where you launched the command. Please read the warning in the following section.

This trick may not work on fast systems, as logout may not have enough time to complete. You may think that using ; instead of & could do the trick (as it will log out the user after resuming), but it allows the user doing a CTRL+C upon resuming, killing the logout command.

From an X session

If you want to lock the computer prior hibernation, you can issue the following command (as root of course):

# xlock & sleep 5 ; pm-hibernate

You can also create the following script:

#!/bin/bash
echo 'Hibernating in 5 seconds'
xlock &
sleep 5
pm-hibernate

xlock is a command that locks your X session. Upon rebooting, you will be asked for the root password. The sleep command may be omitted, but I think it's safer to leave it, so you are sure that xlock has enough time to run properly. You don't have to use exit (or logout) at the end of the command or the script, as it has no use concerning security. You may want to use it though to automatically close the xterm on resuming.

Security warning: this “trick” will only lock the X system! If you are logged on as root in any of the other ttys, xlock can be killed, leaving full access to the X session.
For people using init3 (no automatic X startup), remember to also logout from the tty from where you launched the X system with startx: hit CTRL+Z (to suspend the task), then bg (to resume the task in the background), then CTRL+D (or logout) to logout.

An alternate

If one is a sudoer, ie, can use sudo, then the following can also be used:

sudo /usr/sbin/pm-hibernate

Further reading

Sources


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