SystemD - Services

Properties

Units are representations of resources that systemd knows about.

A Systemd output may show the following columns

• UNIT: The systemd unit name
• LOAD: Loaded in memory ?
• ACTIVE: Does the unit has been successfuly processed ?
• SUB: State information that varies by unit
• DESCRIPTION: description of the unit
• STATE: state of a unit file:
  • “enabled”,
  • “disabled”,
  • “static”:
    • ie the unit file does not contain an “install” section and therefore the unit cannot be enabled
    • used for single action or as a dependency of another units
  • or “masked”.

Unit file

systemctl cat foobar.service

[Unit]
Description=foobar daemon
After=network.target

[Service]
Type=forking
User=infa
; sleep for 5 minutes to ensure headnode is up and running
ExecStartPre=/bin/sleep 300
ExecStart=/usr/bin/daemon startup
ExecStop=/usr/bin/daemon shutdown
TimeoutSec=infinity
TimeoutStartSec=10min 10sec

[Install]
WantedBy=multi-user.target

Example for java with redirections

ExecStart=/bin/sh -c 'exec /bin/java -jar xxx.jar -Xmx512M -Xms32M >> /data/logs/xxx.log 2>&1'

Unit file path

• /usr/lib/systemd/ for files that ships with packages
• /etc/systemd/system/ for admin modification
• /lib/systemd/ ??

Environment

Environment variable possibilities can be seen here: SystemD - Environment Variable for a service

Standard Stream

Redirection of the standard stream of the application.

To query it, see SystemD - Journalctl

Doc

• Create a new file

StandardOutput=file:/home/user/log1.log
StandardError=file:/home/user/log2.log

• Append

StandardOutput=append:/home/user/log1.log
StandardError=append:/home/user/log2.log

Listing

• query the state of all services, both systemd native and SysV/LSB services

systemctl

• List services

systemctl list-units --all --type=service
#-all because list-units command shows only active units by default

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

• To see every unit file if something goes wrong

systemctl list-unit-files

Show

• unit file

systemctl cat foobar.service

• Service properties

systemctl show sshd.service

Timeout

# all timeout property
systemctl show node.service | grep -i Timeout*

# By property
systemctl show node.service -p TimeoutStartSec
systemctl show node.service -p TimeoutStopSec
systemctl show node.service -p TimeoutSec # A shorthand for configuring both TimeoutStartSec= and TimeoutStopSec= to the specified value
# ''-p --property=NAME''  Show only properties by this name

• JobTimeoutUSec
• TimeoutStartSec Configures the time to wait for start-up. If a daemon service does not signal start-up completion within the configured time, the service will be considered failed and will be shut down again. Default to DefaultTimeoutStartSec from the manager configuration file, except when Type=oneshot is used, in which case the timeout is disabled by default . Takes a unit-less value in seconds, or a time span value such as “5min 20s”. Pass “infinity” to disable the timeout logic.

Example

; 15 min
TimeoutSec=900 

Dependency

systemctl list-dependencies sshd.service

sshd.service
├─system.slice
└─basic.target
  ├─microcode.service
  ├─rhel-autorelabel-mark.service
  ├─rhel-autorelabel.service
  ├─rhel-configure.service
  ├─rhel-dmesg.service
  ├─rhel-loadmodules.service
  ├─paths.target
  ├─slices.target
. . .

Start

sudo systemctl start foobar.service

# as systemd knows to look for *.service files for service management commands
sudo systemctl start foobar

Fail If the start fails, systemctl will give you a generic error message:

systemctl start foo.service

Job failed. See system journal and 'systemctl status' for details.

By default:

• the stdout, stderr of services are directed to the systemd journal (journalctl command)
• the logs that services produce via syslog go by default to /var/log/messages and to the SystemD Journal
• systemd stores the exit code of failed services.

Next step:

• Run systemctl status as root or as a user from the adm group to get a journal extract

systemctl status foo.service

• or list the journal with the journalctl command.

journalctl --unit foo

• or list the syslog message (default to /var/log/messages)

Stop

systemctl stop foobar.service

Restart

sudo systemctl restart foobar.service

# if you don't know
sudo systemctl reload-or-restart application.service

Reload

• Reload config file

sudo systemctl reload foobar.service

Active

systemctl is-active application.service

Failed

systemctl is-failed application.service

Enable

Whether the service should start on boot.

sudo systemctl enable foobar.service

# isEnabled
systemctl is-enabled application.service

Disable

sudo systemctl disable foobar.service

Ansible - Disable if exists

- name: Populate service facts
  service_facts:

- name: Disable firewalld
  when: "'firewalld.service' in services"
  systemd:
    name: firewalld
    enabled: no
    state: stopped

Status

systemctl status application.service

Example with cron

systemctl status crond.service

● crond.service - Command Scheduler
   Loaded: loaded (/usr/lib/systemd/system/crond.service; enabled; vendor preset: enabled)
   Active: active (running) since Wed 2019-02-20 14:56:00 UTC; 1 weeks 6 days ago
 Main PID: 6339 (crond)
   CGroup: /system.slice/crond.service
           └─6339 /usr/sbin/crond -n

Install

• Copy the unit script to /etc/systemd/system/

cp foobar.service /etc/systemd/system/

• Restart systemd:

systemctl daemon-reload

• Enable het script voor autorun:

systemctl enable infaservice

• The service can be managed via

systemctl [start|stop|status] foobar

Log

see SystemD - Journalctl