How To Use Systemctl to Manage Systemd Services and Units
How To Use Systemctl to Manage Systemd Services and Units. In this post, we will introduce systemd, its advantages then show you how to manage systemd services and units using systemctl.
Well let’s start with How To Use Systemctl to Manage Systemd Services and Units.
What is Systemd in Linux?
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Systemed in Linux is a system and service manager designed particularly for the Linux kernel. Proposed in 2010, Systemd replaced the widely used sysvinit system to become the first process. Aadditionally, it was executed in user space during the Linux start up process.
Kernel started the sysvinit as the first process to boot up any Linux or Unix computer. After successfully booting the system, it continually runs and waits for appropriate commands like ‘shutdown.’ all in all, it shuts down the Linux system. Simply put, Sysvinit’s process effortlessly shuts down all the tasks in the system.
Basically, it remained the most suitable choice to bring up and shut down the Linux based system for many years. However, with time, it became slow and inflexible for modern computers.
Although both sysvinit and systemd have their advantages, developers decided to replace sysvinit with systemd. Besides, it was atrocious when developers began horsing around with the crucial Linux subsystems. But, if the developers do not like a particular software application, desktop environment, or command, they shift their attention toward its alternatives.
Moreover, since subsystems have deep hooks in the kernel, every management script, and software package dependencies, it is pretty effortless to replace the older version.
In short, things change. Computers are getting more complex and changing the software to meet up with the system requirement is very essential.
Managing Services With Systemd
Some useful systemd utilities are as follows:
- systemctl – Controls the systemd system and services.
- hostnamectl – Controls the hostname.
- timedatectl – Sets the time and date.
- systemadm – Acts as a front end for the systemctl command.
- systemd-cgls – Shows cgroup contents.
- localectl- Configures the system’s local and keyword layout.
- journalctl – Manages the journal and systemd’s own logging system.
Advantages of Systemd
Since 2014, several Linux distributions are relying on the Systemd system and service manager. It provides them with the following advantages:
- Systemd daemons make the process of supervising and controlling processes effortless. Besides, it also makes the execution of parallelized jobs seamless.
- Provides systemctl command and cgroups to make life easier.
- The systemctl utility provides the administrator with more detailed error messages, including runtime errors and startup errors.
- cGroups, also known as ‘Control Groups,’ enables you to group the processes into the hierarchy for effortless management.
- As seen, it is a straightforward process to check process attributes such as function and property. For example, in the Systemd framework, child processes become “children” and are organized in the appropriate “parent” collection to show inheritance.
Please continue reading How To Use Systemctl to Manage Systemd Services and Units.
How To Use Systemctl to Manage Systemd Services and Units
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Systemtd and Systemctl Basics
Before starting, it is important to check whether the systemd is installed on your system. You can check it with the following command:
systemctl --version
If the systemd package is installed, you should see its version in the following output:
systemd 237
+PAM +AUDIT +SELINUX +IMA +APPARMOR +SMACK +SYSVINIT +UTMP +LIBCRYPTSETUP +GCRYPT +GNUTLS +ACL +XZ +LZ4 +SECCOMP +BLKID +ELFUTILS +KMOD -IDN2 +IDN -PCRE2 default-hierarchy=hybrid
Next, check the path of the systemd and systemctl binary with the following command:
whereis systemd
You should see the following output:
systemd: /usr/lib/systemd /bin/systemd /etc/systemd /lib/systemd /usr/share/systemd /usr/share/man/man1/systemd.1.gz
In order to check the path of the systemctl utility, run the following command:
whereis systemctl
Following output should appear:
systemctl: /bin/systemctl /usr/share/man/man1/systemctl.1.gz
Next, it is also important to know whether the systemd is running or not.
ps -eaf | grep [s]ystemd
And then you get the following output:
root 291 1 0 Oct30 ? 00:00:04 /lib/systemd/systemd-journald
root 345 1 0 Oct30 ? 00:00:09 /lib/systemd/systemd-udevd
systemd+ 944 1 0 Oct30 ? 00:00:29 /lib/systemd/systemd-resolved
systemd+ 945 1 0 Oct30 ? 00:00:00 /lib/systemd/systemd-timesyncd
message+ 1255 1 0 Oct30 ? 00:00:13 /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only
Manage Units using Systemctl
Unit files are the primary object in systemd. In turn, that system knows how to operate on and manage. It is a plain text ini-style file that encodes information about a service, a socket, a device, a mount point, an automount point, and a swap file. In this section, we will show you how to manage Units using the systemctl command.
To list all unit types, run the following command:
systemctl -t help
You will get the following list:
Available unit types:
service
socket
target
device
mount
automount
swap
timer
path
slice
scope
After that, to get a list of all installed units, run the following command:
systemctl list-unit-files
You should see the following output:
UNIT FILE STATE
proc-sys-fs-binfmt_misc.automount static
-.mount generated
boot-efi.mount generated
Data.mount generated
dev-hugepages.mount static
dev-mqueue.mount static
proc-fs-nfsd.mount static
proc-sys-fs-binfmt_misc.mount static
run-rpc_pipefs.mount static
Following, to list all running units, use the following command:
systemctl list-units
You should see the following output:
UNIT LOAD ACTIVE SUB DESCRIPTION
proc-sys-fs-binfmt_misc.automount loaded active running Arbitrary Executable File
dev-fuse.device loaded activating tentative /dev/fuse
sys-devices-pci0000:00-0000:00:01.0-backlight-amdgpu_bl0.device loaded active plugged /sys/devices/pci0000:00/00
sys-devices-pci0000:00-0000:00:01.1-sound-card0.device loaded active plugged /sys/devices/pci0000:00/00
sys-devices-pci0000:00-0000:00:02.4-0000:14:00.0-net-enp20s0.device loaded active plugged RTL810xE PCI Express Fast
sys-devices-pci0000:00-0000:00:02.5-0000:16:00.0-net-wlp22s0.device loaded active plugged QCA9377 802.11ac Wireless
sys-devices-pci0000:00-0000:00:09.2-sound-card1.device loaded active plugged /sys/devices/pci0000:00/00
sys-devices-pci0000:00-0000:00:10.0-usb2-2\x2d1-2\x2d1:1.0-bluetooth-hci0.device loaded active plugged /sys/devices/pci0000:00/00
sys-devices-pci0000:00-0000:00:11.0-ata1-host0-target0:0:0-0:0:0:0-block-sda-sda1.device loaded active plugged TOSHIBA_MQ01ABD100 ESP
sys-devices-pci0000:00-0000:00:11.0-ata1-host0-target0:0:0-0:0:0:0-block-sda-sda2.device loaded active plugged TOSHIBA_MQ01ABD100 Micr
sys-devices-pci0000:00-0000:00:11.0-ata1-host0-target0:0:0-0:0:0:0-block-sda-sda3.device loaded active plugged TOSHIBA_MQ01ABD100 OS
sys-devices-pci0000:00-0000:00:11.0-ata1-host0-target0:0:0-0:0:0:0-block-sda-sda4.device loaded active plugged TOSHIBA_MQ01ABD100 4
sys-devices-pci0000:00-0000:00:11.0-ata1-host0-target0:0:0-0:0:0:0-block-sda-sda5.device loaded active plugged TOSHIBA_MQ01ABD100 5
sys-devices-pci0000:00-0000:00:11.0-ata1-host0-target0:0:0-0:0:0:0-block-sda.device loaded active plugged TOSHIBA_MQ01ABD100
sys-devices-platform-serial8250-tty-ttyS0.device loaded active plugged /sys/devices/platform/seri
sys-devices-platform-serial8250-tty-ttyS1.device loaded active plugged /sys/devices/platform/seri
sys-devices-platform-serial8250-tty-ttyS10.device loaded active plugged /sys/devices/platform/seri
Then, to list all failed units, run the following command:
systemctl --failed
Result is the following output:
UNIT LOAD ACTIVE SUB DESCRIPTION
● isc-dhcp-server.service loaded failed failed ISC DHCP IPv4 server
● isc-dhcp-server6.service loaded failed failed ISC DHCP IPv6 server
● mariadb.service loaded failed failed MariaDB 10.1.48 database server
● nginx.service loaded failed failed A high performance web server and a reverse proxy server
● systemd-backlight@backlight:acpi_video0.service loaded failed failed Load/Save Screen Backlight Brightness of backlight:acpi_video0
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.
5 loaded units listed. Pass --all to see loaded but inactive units, too.
To show all installed unit files use 'systemctl list-unit-files'.
If you want to list only service unit files, run the following command:
systemctl list-unit-files -t service
At this point you get the following output:
UNIT FILE STATE
accounts-daemon.service enabled
acpid.service disabled
alsa-restore.service static
alsa-state.service static
alsa-utils.service masked
anacron.service enabled
anydesk.service enabled
apache-htcacheclean.service disabled
apache-htcacheclean@.service disabled
apache2.service enabled
apache2@.service disabled
apparmor.service enabled
apport-autoreport.service static
apport-forward@.service static
apport.service generated
The output has the following columns:
- UNIT: The systemd service unit name
- LOAD: Shows whether the unit definition was properly read and loaded
- ACTIVE: Describes if the unit is active.
- SUB: Low-level activation state of the unit, giving more detailed information about the unit. This will vary by unit type.
- DESCRIPTION: The service unit’s description.
If you want to display the content of specific unit file, run the following comand:
systemctl cat nginx.service
Now, this is the following output:
# /lib/systemd/system/nginx.service
# Stop dance for nginx
# =======================
#
# ExecStop sends SIGSTOP (graceful stop) to the nginx process.
# If, after 5s (--retry QUIT/5) nginx is still running, systemd takes control
# and sends SIGTERM (fast shutdown) to the main process.
# After another 5s (TimeoutStopSec=5), and if nginx is alive, systemd sends
# SIGKILL to all the remaining processes in the process group (KillMode=mixed).
#
# nginx signals reference doc:
# http://nginx.org/en/docs/control.html
#
[Unit]
Description=A high performance web server and a reverse proxy server
Documentation=man:nginx(8)
After=network.target nss-lookup.target
[Service]
Type=forking
PIDFile=/run/nginx.pid
ExecStartPre=/usr/sbin/nginx -t -q -g 'daemon on; master_process on;'
ExecStart=/usr/sbin/nginx -g 'daemon on; master_process on;'
ExecReload=/usr/sbin/nginx -g 'daemon on; master_process on;' -s reload
ExecStop=-/sbin/start-stop-daemon --quiet --stop --retry QUIT/5 --pidfile /run/nginx.pid
TimeoutStopSec=5
KillMode=mixed
[Install]
WantedBy=multi-user.target
To see a unit’s dependency tree, run the following output:
systemctl list-dependencies nginx.service
Get a list of all dependent service units in the following output:
nginx.service
● ├─system.slice
● └─sysinit.target
● ├─apparmor.service
● ├─blk-availability.service
● ├─dev-hugepages.mount
● ├─dev-mqueue.mount
● ├─keyboard-setup.service
● ├─kmod-static-nodes.service
● ├─lvm2-lvmetad.socket
● ├─lvm2-lvmpolld.socket
● ├─lvm2-monitor.service
● ├─plymouth-read-write.service
● ├─plymouth-start.service
● ├─proc-sys-fs-binfmt_misc.automount
● ├─setvtrgb.service
● ├─sys-fs-fuse-connections.mount
● ├─sys-kernel-config.mount
Check the properties of the specific unit file, run the following command:
systemctl show nginx.service
You should see the following output:
Type=forking
Restart=no
PIDFile=/run/nginx.pid
NotifyAccess=none
RestartUSec=100ms
TimeoutStartUSec=1min 30s
TimeoutStopUSec=5s
RuntimeMaxUSec=infinity
WatchdogUSec=0
WatchdogTimestampMonotonic=0
PermissionsStartOnly=no
RootDirectoryStartOnly=no
RemainAfterExit=no
GuessMainPID=yes
MainPID=0
ControlPID=0
FileDescriptorStoreMax=0
NFileDescriptorStore=0
StatusErrno=0
Result=exit-code
UID=[not set]
GID=[not set]
In order to edit the specific unit file, run the following command:
systemctl edit --full nginx.service
This command will allow you to edit the modify the Nginx service file.
Manage Services Using Systemctl
Secondly, the main purpose of the systemd is to manage services and daemons for the server at any point while the system is running. Basic syntex to manage services is shown below:
systemctl [action] service-name
Start the Nginx service, run the following command:
systemctl start nginx
Stop the Nginx service, run the following command:
systemctl stop nginx
Then to restart the Nginx service, run the following command:
systemctl restart nginx
Reload the Nginx service, run the following command:
systemctl reload nginx
Well and to start the Nginx service at system reboot, run the following command:
systemctl enable nginx
Check the status of the Nginx service, run the following command:
systemctl status nginx
Also check the active or in-active status of the Nginx service using the following command:
systemctl is-active nginx
Now to check whether the service is in a enabled state, run the following command:
systemctl is-enabled nginx
To kill the Nginx service, run the following command:
systemctl kill nginx
Alternatively, to mask the Nginx service and make it impossible to start, run the following command:
systemctl mask nginx
You should see the following output:
Created symlink /etc/systemd/system/nginx.service → /dev/null.
To unmask it again, run the following command:
systemctl unmask nginx
You will get the following output:
Removed /etc/systemd/system/nginx.service.
Manage Mount Points using Systemctl
Evidently, using systemd, you can also mount, unmount, remount, reload system mount points and also check the status of mount points. Forthwith, to get a list of all system mount points, run the following command:
systemctl list-unit-files --type=mount
You should see the following list:
UNIT FILE STATE
-.mount generated
boot-efi.mount generated
Data.mount generated
dev-hugepages.mount static
dev-mqueue.mount static
proc-fs-nfsd.mount static
proc-sys-fs-binfmt_misc.mount static
run-rpc_pipefs.mount static
From the above list, start ad stop the Data.mount using the following command:
systemctl start Data.mount
systemctl stop Data.mount
Hence, in order to check the status of the Data.mount, run the following command:
systemctl status Data.mount
You should see the status of the mount in the following output:
● Data.mount - /Data
Loaded: loaded (/etc/fstab; generated)
Active: active (mounted) since Sun 2022-10-30 09:37:24 IST; 2 days ago
Where: /Data
What: /dev/sda5
Docs: man:fstab(5)
man:systemd-fstab-generator(8)
Tasks: 0 (limit: 4915)
CGroup: /system.slice/Data.mount
Oct 30 09:37:24 vyompc systemd[1]: Mounting /Data...
Oct 30 09:37:24 vyompc systemd[1]: Mounted /Data.
To reload the Data.mount, run the following command:
systemctl reload Data.mount
To mask and unmask Data.mount, run the following command:
systemctl mask Data.mount
systemctl unmask Data.mount
Manage Sockets using Systemctl
Indeed, the basic syntax to manage sockets using the systemctl command is shown below:
systemctl [action] socket-name
To get a list of all system sockets, run the following command:
systemctl list-unit-files --type=socket
You should see all sockets in the following output:
UNIT FILE STATE
acpid.socket enabled
apport-forward.socket enabled
avahi-daemon.socket enabled
cups.socket enabled
dbus.socket static
dm-event.socket enabled
docker.socket enabled
epmd.socket disabled
lvm2-lvmetad.socket enabled
lvm2-lvmpolld.socket enabled
rpcbind.socket enabled
saned.socket disabled
snapd.socket enabled
ssh.socket disabled
From the above list, start the docker.socket using the following command:
systemctl start docker.socket
Likewise, to stop the docker.socket, run the following command:
systemctl stop docker.socket
To check the status of the docker.socket, run the following command:
systemctl status docker.socket
If you want to check the active status, run the following command:
systemctl is-active docker.socket
Later, to mask and unmask docker.sockets, run the following command:
systemctl mask docker.socket
systemctl unmask docker.socket
Thank you for reading How To Use Systemctl to Manage Systemd Services and Units. We shall conclude.
How To Use Systemctl to Manage Systemd Services and Units Conclusion
In this guide, we explained systemd units in more detail and how to use the systemctl command to explore and manage units. We also show you how to manage services, mounts and sockets using the systemctl command. The systemctl utility is very useful for system administrator for service and system state management.
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