UNIX Services

UNIT LOAD ACTIVE SUB DESCRIPTION accounts-daemon.service loaded active running Accounts Service alsa-state.service loaded active running Manage Sound Card State (restore and store) atd.service loaded active running Job spooling tools auditd.service loaded active running Security Auditing Service avahi-daemon.service loaded active running Avahi mDNS/DNS-SD Stack chronyd.service loaded active running NTP client/server colord.service loaded active running Manage, Install and Generate Color Profiles crond.service loaded active running Command Scheduler cups.service loaded active running CUPS Scheduler dbus.service loaded active running D-Bus System Message Bus dracut-shutdown.service loaded active exited Restore /run/initramfs on shutdown firewalld.service loaded active running firewalld - dynamic firewall daemon gdm.service loaded active running GNOME Display Manager geoclue.service loaded active running Location Lookup Service gssproxy.service loaded active running GSSAPI Proxy Daemon import-state.service loaded active exited Import network configuration from initramfs irqbalance.service loaded active running irqbalance daemon iscsi-shutdown.service loaded active exited Logout off all iSCSI sessions on shutdown iscsid.service loaded active running Open-iSCSI kdump.service loaded active exited Crash recovery kernel arming kmod-static-nodes.service loaded active exited Create list of required static device nodes for the current kernel libstoragemgmt.service loaded active running libstoragemgmt plug-in server daemon lvm2-monitor.service loaded active exited Monitoring of LVM2 mirrors, snapshots etc. using dmeventd or progress pollinglvm2-pvscan@251:16.service loaded active exited LVM event activation on device 251:16 lvm2-pvscan@251:3.service loaded active exited LVM event activation on device 251:3 lvm2-pvscan@251:32.service loaded active exited LVM event activation on device 251:32 lvm2-pvscan@251:48.service loaded active exited LVM event activation on device 251:48 ModemManager.service loaded active running Modem Manager NetworkManager-wait-online.service loaded active exited Network Manager Wait Online NetworkManager.service loaded active running Network Manager nis-domainname.service loaded active exited Read and set NIS domainname from /etc/sysconfig/network packagekit.service loaded active running PackageKit Daemon plymouth-quit-wait.service loaded active exited Hold until boot process finishes up plymouth-read-write.service loaded active exited Tell Plymouth To Write Out Runtime Data plymouth-start.service loaded active exited Show Plymouth Boot Screen polkit.service loaded active running Authorization Manager qemu-guest-agent.service loaded active running QEMU Guest Agent rpc-statd-notify.service loaded active exited Notify NFS peers of a restart rsyslog.service loaded active running System Logging Service rtkit-daemon.service loaded active running RealtimeKit Scheduling Policy Service serial-getty@ttyAMA0.service loaded active running Serial Getty on ttyAMA0 smartd.service loaded active running Self Monitoring and Reporting Technology (SMART) Daemon spice-vdagentd.service loaded active running Agent daemon for Spice guests sshd.service loaded active running OpenSSH server daemon sssd-kcm.service loaded active running SSSD Kerberos Cache Manager sysstat.service loaded active exited Resets System Activity Logs systemd-binfmt.service loaded active exited Set Up Additional Binary Formats systemd-fsck@dev-disk-by\x2duuid-79F0\x2dE46A.service loaded active exited File System Check on /dev/disk/by-uuid/79F0-E46A systemd-fstab-generator-reload-targets.service loaded active exited systemd-fstab-generator-reload-targets.service systemd-journal-flush.service loaded active exited Flush Journal to Persistent Storage systemd-journald.service loaded active running Journal Service systemd-logind.service loaded active running Login Service systemd-modules-load.service loaded active exited Load Kernel Modules systemd-random-seed.service loaded active exited Load/Save Random Seed systemd-remount-fs.service loaded active exited Remount Root and Kernel File Systems systemd-sysctl.service loaded active exited Apply Kernel Variables systemd-tmpfiles-setup-dev.service loaded active exited Create Static Device Nodes in /dev systemd-tmpfiles-setup.service loaded active exited Create Volatile Files and Directories systemd-udev-settle.service loaded active exited udev Wait for Complete Device Initialization systemd-udev-trigger.service loaded active exited udev Coldplug all Devices systemd-udevd.service loaded active running udev Kernel Device Manager systemd-update-utmp.service loaded active exited Update UTMP about System Boot/Shutdown systemd-user-sessions.service loaded active exited Permit User Sessions tuned.service loaded active running Dynamic System Tuning Daemon udisks2.service loaded active running Disk Manager upower.service loaded active running Daemon for power management user-runtime-dir@1000.service loaded active exited User runtime directory /run/user/1000 user@1000.service loaded active running User Manager for UID 1000 wpa_supplicant.service loaded active running WPA supplicant
LOAD = Reflects whether the unit definition was properly loaded.ACTIVE = The high-level unit activation state, i.e. generalization of SUB.SUB = The low-level unit activation state, values depend on unit type.
69 loaded units listed. Pass --all to see loaded but inactive units, too.To show all installed unit files use 'systemctl list-unit-files'.

Start

systemctl start myservice

Stop

systemctl stop myservice

Restart/Reload

Mask/UnMask

systemctl restart myservice

systemctl reload myservice

systemctl reload-or-restart myservice

Masking prevents a service being started (either manually or automatically)...

systemctl mask myservice

systemctl unmask myservice

Configuration

touch /etc/systemd/system/myservice.service

chmod 644 /etc/systemd/system/myservice.service

You may also find .service files in.../usr/lib/systemd/systemThis directory contains distribution level packages which will be overridden by any files in /etc/systemd/system. Always put your custom service files in /etc/systemd/system.

The unit file for your service should have [Unit] and [Service] sections.
Without an [Install] section you will be able to start manually, but you won't be able to 'enable' it for automatic startup.

[Unit]

Description - a short human readable name of the unit (service).

Documentation - a space seperated list of URIs of type http:, https:, file:, infor: or man:

Wants - lists units that systemd will attempt to start (if they are not already active) when this unit starts. If wanted units fail to start this unit will still start.

Requires - lists units that systemd will attempt to start (if they are not already active) when this unit starts. If required units fail to start this unit will also fail to start.

Requisite - if listed units are not already active then this unit will fail to start.

BindsTo - like Requires but if the bound to unit becomes inactive then this unit will stop.

[Install]

WantedBy - has the same effect as putting a Wants entry for this unit in the Unit section of the named unit's unit file. It does this via symbolic links (created when you enable) rather than updating the target unit file itself. The symbolic link is removed when you disable.

RequiredBy -similar to WantedBy but has the same affect as a Requires entry for this unit in the Unit section of the named unit's unit file.

For MySQL...

Example taken from MySQL documentation...[Unit]Description=MySQL ServerDocumentation=man:mysqld(8)Documentation=http://dev.mysql.com/doc/refman/en/using-systemd.htmlAfter=network.targetAfter=syslog.target
[Service]User=mysqlGroup=mysqlType=notifyTimeoutSec=0ExecStart=/mysql/current/bin/mysqld --defaults-file=/mysql/my.cnf $MYSQLD_OPTS EnvironmentFile=-/etc/sysconfig/mysqlLimitNOFILE = 10000Restart=on-failureRestartPreventExitStatus=1Environment=MYSQLD_PARENT_PID=1PrivateTmp=false
[Install]WantedBy=multi-user.target

For MySQL Router...

From Oracle Support Note 2684939.1[Unit]Description=MySQL RouterAfter=syslog.targetAfter=network.target
[Service]Type=simpleUser=mysqlrouterGroup=mysqlrouterPIDFile=/var/run/mysqlrouter/mysqlrouter.pidExecStart=/usr/bin/mysqlrouter -c /etc/mysqlrouter/mysqlrouter.confRestart=on-failurePrivateTmp=true
[Install]WantedBy=multi-user.target

For Oracle Database...

[Unit]Description=Oracle Database & ListenerAfter=syslog.target network.target
[Service]Type=simpleUser=oracleGroup=oinstallLimitNOFILE=65536LimitNPROC=16384LimitSTACK=32MLimitMEMLOCK=infinityLimitCORE=infinityLimitDATA=infinityExecStart=/bin/bash -c 'source /home/oracle/.bash_profile && dbstart $ORACLE_HOME'ExecStop=/bin/bash -c 'source /home/oracle/.bash_profile && dbshut $ORACLE_HOME'RemainAfterExit=yesRestart=noTimeoutStopSec=5min
[Install]WantedBy=multi-user.target

[Service]

Type - simple / exec / forking / oneshot / dbus / notify / idle - if in doubt, use simple. notify expects the service to send a notification message (via sd_notify or equivalent) when it has finished starting up.

User - sets the user that the processes are executed as.

Group - sets the group that the processes are executed as.

TimeoutSec - configures both TimeoutStartSec and TimeoutStopSec to the specified value.

TimeoutStartSec - configures the time to wait for startup. Pass "infinity" (or "0" to disable timeout logic. Services of type "Notify" are able to send "EXTEND_TIMEOUT_USEC=" calls to extend startup beyond TimeoutStartSec.

TimeoutStopSec - configures the time to wait for each ExecStop command. Also configures time to wait for service itself to stop. Pass "infinity" (or "0") to disable timeout logic. Services of type "Notify" are able to send "EXTEND_TIMEOUT_USEC=" calls to extend startup beyond TimeoutStopSec.

ExecStart - commands, with their arguments, that are executed when the service is started.

EnvironmentFile - specifies a file containing variable definitions.
Note that, although taken directly from the MySQL installation guide, the value "-/etc/sysconfig/mysql" is invalid due to the leading "-" (and on my test system, this file doesn't exist anyway) - the comment reads "Use this to switch malloc implementation", which may warrant further investigation (TODO)

Environment - variable definitions. E.g. for mysql setting MYSQLD_PARENT_PID to 1 is required for MySQL restart.

Restart - no (default) / always /
on-success / on-failure / on-abnormal / on-abort / on-watchdog. If you want your service to restart if it crashes but not if it cleanly exits, then use on-failure.

RestartPreventExitStatus - contains list of exit codes or signals that will not cause a restart even if they meet the criteria for the Restart setting.

LimitNOFILE - Sets open_files_limit (equivalent to ulimit -n)

PrivateTmp - If true, sharing between processes via /tmp/ or /var/tmp/ impossible and all temporary files created by a service in /tmp or /var/tmp will be removed after the service is stopped.

PIDFile - Takes a path referring to the PID file of the service. Usage of this option is recommended for services where Type= is set to forking.

RemainAfterExit

systemctl daemon-reload

Run this after each change of the unit file (i.e. the .service file).

If you don't, you will get a warning when you try to start the service.Warning: The unit file, source configuration file or drop-ins of dbora.service changed on disk. Run 'systemctl daemon-reload' to reload units.

Automatically Start at Boot

systemctl enable myservice

systemctl disable myservice

Examples

MySQL Router

MySQL

Apache Tomcat

Oracle

Diagnostics

systemctl status service

journalctl -xe

list-units

To list all active units (services) that systemctl knows about...

systemctl list-units

To list only MySQL related active units...

systemctl list-units | grep mysql

mysql.mount loaded active mounted /mysqlmysqld.service loaded active running MySQL Servermysqlrouter.service loaded active running MySQL Router

To list all units that systemd has tried to load regardless of current state...

systemctl list-units --all

systemctl list-units --all | grep mysql

To list only inactive units...

systemctl list-units --all --state=inactive

list-unit-files

To see every available unit file within the systemd paths, including those that systemd has not attempted to load...

systemctl list-unit-files

systemctl list-unit-files | grep mysql

mysqld.service enabled mysqlrouter.service enabled

STATE returned will be one of...

enabled - will auto start
disabled - won't auto start
static - cannot be enabled (but could perform a one-off action or could be used as a dependency of another unit)
masked - cannot be started (service is linked to /dev/null).

list-dependencies

systemctl list-dependencies myservice

Outputs a dependency tree of all units that are either required or wanted by your service.

systemctl list-dependencies --all myservice

Recursively lists all dependencies

systemctl list-dependencies --before myservice

systemctl list-dependencies --after myservice

show

systemctl show myservice

Shows the low-level properties of your service

systemctl show myservice -p After

Shows just the After property for your service

systemd-sysv-generator

TODO

systemd-analyze

systemd-analyze blame

TODO

Bibliography

https://www.digitalocean.com/community/tutorials/how-to-use-systemctl-to-manage-systemd-services-and-unitshttps://unix.stackexchange.com/questions/379363/how-can-i-start-systemd-service-units-in-orderhttps://askubuntu.com/questions/710420/why-are-some-systemd-services-in-the-masked-statehttps://stackoverflow.com/questions/30782811/how-do-i-list-all-systemd-masked-unitshttps://www.devdungeon.com/content/creating-systemd-service-fileshttps://www.freedesktop.org/software/systemd/man/systemd.unit.html#https://www.freedesktop.org/software/systemd/man/systemd.service.htmlhttps://www.freedesktop.org/software/systemd/man/systemd.exec.htmlhttps://www.freedesktop.org/software/systemd/man/systemd.kill.html#https://www.freedesktop.org/software/systemd/man/systemd-run.html#https://www.freedesktop.org/software/systemd/man/systemd-sysv-generator.html#https://oracle-base.com/articles/linux/linux-services-systemd
https://serverfault.com/questions/482730/systemd-dependencies-and-boot-orderhttps://serverfault.com/questions/736624/systemd-service-automatic-restart-after-startlimitinterval/962338
https://www.zdnet.com/article/nasty-linux-systemd-root-level-security-bug-revealed-and-patched/
systemd-analyzehttps://www.man7.org/linux/man-pages/man1/systemd-analyze.1.html
MySQLRouterhttps://support.oracle.comHow to Make MySQL Router Automatically Restart on Systemd (Doc ID 2684939.1)