Systemd

Introduction

The main aim of systemd (a "system and service manager") is to unify service configuration and behavior across Linux distributions. It bootstraps the user space and manages user processes. It also provides replacements for various daemons and utilities, including device management, login management, network connection management, and event logging.

Since 2015, the majority of Linux distributions have adopted systemd, having replaced other init systems such as SysV init.

Preventing shutdown and reboot while VDR is running

By default, the power button on a remote control that is managed by a kernel LIRC driver will be mapped to systemd-logind. Unless you have overridden the default HandlePowerKey=poweroff in /etc/systemd/logind.conf, the system would be shut down immediately when you hit a power button on any input device (remote control, keyboard, or power button on the computer case).

Often, VDR is the main application on the system. You would not want the system to be accidentally shut down or rebooted while someone is watching TV, or a recording is in progress. System shutdown would be initiated by a script that would be invoked by VDR itself; see the -s parameter of ExecStart below.

To disable or enable the normal handling of shutdown and reboot, you can use the following script, say, /etc/systemd/system/vdr-keep-alive.sh. Executing it will require super user privileges.

#!/bin/sh

TARGETS="
/lib/systemd/system/poweroff.target.d
/lib/systemd/system/reboot.target.d
/lib/systemd/system/halt.target.d
"
CONF=vdr-keep-alive.conf

case "$1" in
start)
  for t in $TARGETS
  do
    if [ ! -f "$t/$CONF" ]
    then
      if [ ! -d "$t/" ]
      then
        mkdir "$t"
      fi
      echo "[Unit]\nRefuseManualStart=yes" > "$t/$CONF"
    fi
  done
  ;;
stop)
  for t in $TARGETS
  do
    rm -f "$t/$CONF"
  done
  ;;
esac

exec systemctl daemon-reload

You can execute this script as follows:

sudo /etc/systemd/system/vdr-keep-alive.sh start
sudo /etc/systemd/system/vdr-keep-alive.sh stop

You might want to make the TARGETS above to include suspend, hibernate, or others mentioned in man 7 systemd.special.

Making Systemd start up VDR

Before systemd, you might have edited /etc/gettydefs to prevent a virtual console from being associated with a normal login prompt, and then have init invoke a shell script that would invoke VDR, often named runvdr. With systemd, all you need is a single file, say, /etc/systemd/system/vdr.service, with contents like the following:

[Unit]
Description=Video Disk Recorder
After=systemd-user-sessions.service plymouth-quit-wait.service
After=rc-local.service
After=getty@tty1.service
Conflicts=getty@tty1.service
Conflicts=shutdown.target
ConditionPathExists=/video/video

[Service]
User=pi
ExecStartPre=+/etc/systemd/system/vdr-keep-alive.sh start
ExecStart=/usr/local/bin/vdr --no-kbd --lirc=/dev/lirc0 -Prpihddevice -v /video/video -s /var/lib/vdr/vdr-shutdown.sh
TimeoutStartSec=infinity
Type=idle
Restart=on-failure
RestartSec=1s
TTYVTDisallocate=yes
[Install]
WantedBy=display-manager.service

Adjustments

• User= refers to the user account that will run the VDR service.
• ExecStart= must refer to the full VDR invocation.
• ConditionPathExists= is for the directory that contains the recordings, matching the -v parameter in ExecStart. If the recordings cannot be mounted, the service would not start up.

The shutdown script (named /var/lib/vdr/vdr-shutdown.sh in the above example) could do at least one of the following:

• Invoke sudo /etc/systemd/system/vdr-keep-alive.sh stop to allow normal reboot and shutdown.
• Adjust rtcwake (or Nvram_wakeup) to have the system start up automatically on the next scheduled recording.
• Invoke sudo systemctl stop vdr or sudo systemctl halt to shut down VDR or the entire system. This will also terminate the shell that runs the script!

Installation

sudo systemctl enable vdr
sudo systemctl start vdr

or just (according to man systemctl):

sudo systemctl enable --now vdr

Example: Auto-starting VDR with swappable video storage

On a small system like the Raspberry_Pi, the internal storage is just large enough for the basic installation and system configuration. For recordings, you might want to use a USB-powered HDD or SSD.

You might make a virtue out of necessity and implement swappable video directories. One USB SSD might not be large enough for your entire collection of recordings. So, why not implement swappable storage, with the following user interface?

1. When you plug in the USB cable (or it is attached on system startup), VDR will start up automatically.
2. When you press the power button, VDR will shut down and the USB storage will be powered off, so that it can be safely unplugged.
3. When you plug in the USB cable again, VDR will start up again. This could be a different drive.

Preparations

Create a file system and label it VDR. Create the subdirectory video inside it.

Below, we assume that the storage devices that you want to initialize is /dev/sdd. Substitute the correct name for sdd below, and ensure that you are accessing the right device!

sudo mkfs.ext4 /dev/sdd1
sudo tune2fs -L /dev/sdd1
sudo mount /dev/sdd1 /mnt
mkdir /mnt/video
sudo umount /mnt

On the VDR system, create a mount point for the storage devices that have been prepared as above.

sudo mkdir -m 000 /video

Automatically mounting storage when it is plugged in

You might think of a simple /etc/fstab entry like this:

LABEL=VDR /video ext4 defaults,noatime,nofail 0 1

But, we want the file system to be mounted automatically when it is labeled VDR. To achieve that, we create a file /etc/systemd/system/video.mount (the name must match the mount point /video):

[Unit]
BindsTo=dev-disk-by\x2dlabel-VDR.device
After=dev-disk-by\x2dlabel-VDR.device
Requires=systemd-fsck@dev-disk-by\x2dlabel-VDR.service
After=systemd-fsck@dev-disk-by\x2dlabel-VDR.service

[Mount]
Where=/video
What=/dev/disk/by-label/VDR
Type=ext4
Options=defaults,noatime,nofail

[Install]
WantedBy=dev-disk-by\x2dlabel-VDR.device

The magic .device unit refers to the path /dev/disk/by-label/VDR, which will become available when a device containing a file system labeled VDR is attached. We use that name also in the What= directive.

Now we are ready to enable the unit:

sudo systemctl enable video.mount

To check the status, you may find the following commands useful:

systemctl status
journalctl -u video.mount
journalctl -xe

Automatically starting VDR when the storage is plugged in

We also want VDR to start automatically once the file system has been mounted. To do that, the following lines have to be added to /etc/systemd/system/vdr.service:

[Install]
WantedBy=dev-disk-by\x2dlabel-VDR.device

If you had the following lines at the end of the file, they can be removed:

[Install]
WantedBy=display-manager.service

To notify systemd of the update:

sudo systemctl reenable vdr

Last, we need a VDR shutdown script /var/lib/vdr/vdr-shutdown.sh that will power off the storage so that it can be safely detached:

#!/bin/sh
#exec >> /var/tmp/vdr-shutdown.txt 2>&1; set -x; : "$@"
set -eu
BOOT_DELAY=120 # seconds
#FALLBACK_SHUTDOWN_DELAY=86400 # seconds
STORAGE=/dev/disk/by-label/VDR
[ -n "${STORAGE:-}" ] && sudo systemd-mount -u "$STORAGE"
if [ "$2" = 0 ]
then
  sudo sh /etc/systemd/system/vdr-keep-alive.sh stop
  sudo rtcwake -m disable || :
  sudo systemctl poweroff
elif [ "$5" = 1 ]
then
  sudo rtcwake -m no -s "$2" || :
  sudo sh /etc/systemd/system/vdr-keep-alive.sh stop
  [ -n "${STORAGE:-}" ] && sudo udisksctl power-off -b "$STORAGE"
elif [ "$2" -ge $BOOT_DELAY ] && sudo rtcwake -m disk -s $(($2 - $BOOT_DELAY / 2))
then
  :
elif sudo rtcwake -m mem -s "$2"
then
  :
elif [ "$2" -ge "${FALLBACK_SHUTDOWN_DELAY:-}" ]
then
  sudo sh /etc/systemd/system/vdr-keep-alive.sh stop
  sudo systemctl poweroff
fi
[ -n "${STORAGE:-}" ] && sudo systemd-mount "$STORAGE"

Notes

You can still execute the following commands to stop or start the VDR service, for example, for upgrading VDR or plugins:

sudo systemctl stop vdr
sudo systemctl start vdr

If you use these commands, the storage device will remain mounted in the file system, and the status of the reboot and shutdown targets will not change.

At the start of the /var/lib/vdr/vdr-shutdown.sh script, you can configure a few things.

1. Replace the #exec with exec to enable debug output to the file /var/tmp/vdr-shutdown.txt. This file should survive system shutdown and restart.
2. Adjust BOOT_DELAY to the time it takes to shutdown and restart your system, or to suspend to disk and resume from it.
3. If you do not want to use detachable storage for the video storage, remove or comment out the line starting with STORAGE=.

If the power button is pressed while VDR is not running, the system will be shut down. On the first press (while VDR is running), the lines after elif [ "$5" = 1 ] will detach the storage and shut down VDR. Some systems do not support wake-on-timer after power-off; see rtcwake for details. On such systems, you might remove the section elif [ "$5" = 1 ] to let the power button press to lead to proceed to suspend-to-disk or suspend-to-RAM instead.

If the STORAGE variable has been set, and any process (VDR or anything else) is using that mount point, the system will refuse to shut down. The power LED indicator on a USB storage device will become an indicator on whether shutdown is possible. If VDR is the only user of STORAGE, an extremely slow "double click" of the power button on the remote control unit will power off the system. Note: An active recording or the playback of a recording (even a paused playback) will prevent shutdown.

The /var/lib/vdr/vdr-shutdown.sh script relies on the versatile command rtcwake for wake-on-timer control. Suspending to disk could fail because no swap space has been configured. The script can fall back to suspend-to-RAM. If there is no real-time clock device for scheduling wake-up (say, on a Raspberry Pi), it would then be the user's responsibility to shut down or wake up the system between recordings. You might want to set FALLBACK_SHUTDOWN_DELAY at the start of the script to have an automatic shutdown (followed by manual wakeup) if the next scheduled recording is in distant enough future.