systemd-custom-unit

2022-04-08 :: system, systemd, tutorial

By: Maciej Barć

Template

File: /etc/systemd/system/APP.service

[Unit]
Description=Run APP application

[Service]
Type=simple
ExecStart=/usr/bin/LANG APP_DIR/APP APP_ARGS
Restart=on-failure
User=root
WorkingDirectory=APP_DIR

[Install]
WantedBy=multi-user.target

Also, the application might need to reference a PID file, let systemD know abut it via PIDFile.

1	PIDFile=/tmp/APP.pid

Example

File: /etc/systemd/system/julia_dash_app.service

[Unit]
Description=Run Julia Dash application

[Service]
Type=simple
ExecStart=/usr/bin/julia /root/julia_dash_app/main.jl
Restart=on-failure
User=root
WorkingDirectory=/root/julia_dash_app

[Install]
WantedBy=multi-user.target

systemd

2020-05-23 :: linux, openrc, system, systemd

By: Maciej Barć

Init basic functions

Init should:

be the first started process - PID 1
continue running until the system is shut down

Why systemd is more than init

Full system management

systemd needs to run as PID 1 to parenthood other services and… other parts of itself (listed below).

sytemd absorbed

cron -> timers
seat tracker -> systemd-logind
service manager -> systemd-systemctl
udev -> systemd-udevd
system logger -> systemd-journald
network manager -> systemd-networkd
bootloader -> systemd-boot
hostname -> systemd-hostnamed
chroot -> systemd-nspawn
resolv.conf generator -> systemd-resolved

Additionally systemd is also

QR code generator
http server (cockpit)
home manager -> systemd-homed
tmp manager -> systemd-tmpfiles

Why it's bad

systemd growth to cover more and more of other services capabilities is dangerous. It can mean that if we find a exploit in one part of systemd it will be easy to compromise the whole system. Actually, there is a even bigger problem - most of the time a user would like to run a standalone service covering one of the uses already covered by systemd - like cronie or rsyslog.

But what about cgroups

Cgroups are nothing new, they are available in other service managers too. Check out cgroups in OpenRC.

Alternatives

OpenRC

Primarily used by Gentoo based systems. Was adopted to Devuan and Artix. Alpine Linux uses it probably because it started out as a Gentoo-based system. Is also available in Debian - though that will still use some systemd services, notably systemd-udevd.

Runit

Avalible in Void Linux - the recommended init for that system.

Pure System V init

Most popular use of this is found in old CentOS, Slackware, Antix and MX Linux.

S6

Check out Devuan if you want to dive into this topic.

systemd + Emacs

One could think that because systemd and Emacs cover a lot of things - systemd - system management and emacs - user utilities - a fusion of two would be very good and will lack so-called bloat. There is one "problem" however - Emacs can be used also as a init! And that doesn't necessarily mean a lot more code being added. So i guess Emacs + Linux (kernel) is the way to go ;P

Was systemd a inside job?

Probably not - Microsoft made their own init for Azure because… systemd was to big… systemd is a history of what happens when everybody wants to be like the rest - adoption of systemd.

Is systemd the new busybox?

This is an interesting concept. There is one bad thing however - you can compile bysybox with any of its utilities and it will work - you can't do that with systemd, you will have to modify and fork it - like eudev and elogind projects

OpenRC prejudice

Many people think of OpenRC as a old SysVinit. I encourage you to check it out and see that most stuff you probably do with systemd you can get from OpenRC (service manager) + cronie (cron/timers) + htop/pstree (full description of system as opposed to "systemctl status")

Basic OpenRC vs systemd commands

OpenRC systemd ————————— ————————— rc-status -a systemctl status rc-service SERVICE start systemctl start SERVICE rc-service SERVICE stop systemctl stop SERVICE rc-update add SERVICE systemctl enable SERVICE rc-update del SERVICE systemctl disable SERVICE

Posts tagged systemd