List all processed with their cgroups, lots of them are managed by systemd:
ps xawf -eo pid,user,cgroup,args
Restart=restart-always, RestartSec=2s: always restart the service no matter what exit code returned, restart after 2s.
OOMScoreAdjust=-500: adjust OOM score to a negative value, tells OOMKiller
to kill processes with a higher score first.
Useful for a system-critical things.
CPUSchedulingPolicy=idle: schedule the service only when a system is in idle state.
Useful for less imprtant, periodic tasks like backups, or log rotation.
ReadOnlyDirectories=, InaccessibleDirectories=: control directories access for a process.
Add SystemMaxUse=1G to the unit file to set the desired amount of logs for a service.
journalctl --disk-usage
journalctl --vacuum-size=1G
journalctl --list-boots
Run systemctl commands on a remote machine, user@addr is the same as for ssh:
systemctl -H user@addr <args>
systemd-nspawn is a "better chroot".
Quite useful parameters are custom network config,
readonly filesystem, ephemeral filesystem that does not keep changes.
How to run Debian stabe on your machine:
# download and unpack debian system into "debian-tree"
# note that "unstable" snapshot won't boot
sudo debootstrap --arch=amd64 --include=systemd,systemd-sysv,bash stable debian-tree/ http://ftp.am.debian.org/debian/
# start the system
sudo systemd-nspawn --boot --network-veth -D debian-tree
see also:
-p | --port forward host's port into a concainer system.
-n | --network-veth create and attach network bridge interface into a container.
Add LogNamespace=xxx to your unit files in [Service] section, then read logs for a whole namespace usign journalctl --namespace xxx.
As well as ExecStart, there is also ExecStop, so it's possible to customize what systemctl stop service does:
ExecStop=/bin/kill -s SIGINT -$MAINPID & /bin/kill -s SIGINT -$MAINPID
Also, there is systemctl reload command, this is how its behavior might be customzied:
ExecReload=/usr/sbin/sshd -t
ExecReload=/bin/kill -HUP $MAINPID
[Service]
Environment="KEY=value"
Environment="DEBUG=true"
Repeat Environment as much as you have to.