Linux systemd

Manage Systemd Services and Units using Systemctl

Systemctl is a systemd utility which is responsible for Controlling the systemd system and service manager.

Systemd is a collection of system management daemons, utilities and libraries which serves as a replacement of System V init daemon. Systemd functions as central management and configuration platform for UNIX like system.

In the Linux Ecosystem Systemd has been implemented on most of the standard Linux Distribution with a few exception. Systemd is the parent Process of all other daemons oftenly but not always.

Check versions, binaries and libraries

$ systemd --version #Ubuntu 18.04
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
$ whereis systemd
systemd: /usr/lib/systemd /bin/systemd /etc/systemd /lib/systemd /usr/share/systemd /usr/share/man/man1/systemd.1.gz
$ whereis systemctl
systemctl: /bin/systemctl /usr/share/man/man1/systemctl.1.gz

Is systemd running?

ps -eaf | grep [s]ystemd

Analyze

Analyze systemd boot process

# systemd-analyze

Analyze time taken by each process at boot

# systemd-analyze blame

Analyze critical chain at boot

# systemd-analyze critical-chain

Important: Systemctl accepts services (.service), mount point (.mount), sockets (.socket) and devices (.device) as units

List units

systemctl list-unit-files #List all the available units
systemctl list-units      #List all running units
systemctl --failed        #List all failed units

systemctl is-enabled crond.service #Check if a Unit (cron.service) is enabled
systemctl status firewalld.service #Check whether a Unit or Service is running

Control and Manage Services Using Systemctl

List all services (including enabled and disabled)

systemctl list-unit-files --type=service

How do I start, restart, stop, reload and check the status of a service (httpd.service) in Linux

systemctl start   httpd.service
systemctl restart httpd.service
systemctl stop    httpd.service
systemctl reload  httpd.service
systemctl status  httpd.service

Note: When we use commands like start, restart, stop and reload with systemctl, we will not get any output on the terminal, only status command will print the output

How to active a service and enable or disable a service at boot time (auto start service at system boot)

systemctl is-active httpd.service
systemctl enable  httpd.service
systemctl disable httpd.service

How to mask (making it impossible to start) or unmask a service (httpd.service)

systemctl mask   httpd.service
systemctl unmask httpd.service

How to a Kill a service using systemctl command

systemctl kill   httpd
systemctl status httpd

Control and Manage Mount Points using Systemctl

List all system mount points

# systemctl list-unit-files --type=mount

How do I mount, unmount, remount, reload system mount points and also check the status of mount points on the system

# systemctl start tmp.mount
# systemctl stop tmp.mount
# systemctl restart tmp.mount
# systemctl reload tmp.mount
# systemctl status tmp.mount

How to active, enable or disable a mount point at boot time (auto mount at system boot)

# systemctl is-active tmp.mount
# systemctl enable tmp.mount
# systemctl disable  tmp.mount

How to mask (making it impossible to start) or unmask a mount points in Linux

# systemctl mask tmp.mount
# systemctl unmask tmp.mount

Control and Manage Sockets using Systemctl

List all available system sockets

# systemctl list-unit-files --type=socket

How do I start, restart, stop, reload and check the status of a socket (example: cups.socket) in Linux

# systemctl start cups.socket
# systemctl restart cups.socket
# systemctl stop cups.socket
# systemctl reload cups.socket
# systemctl status cups.socket

How to active a socket and enable or disable at boot time (auto start socket at system boot)

# systemctl is-active cups.socket
# systemctl enable cups.socket
# systemctl disable cups.socket

How to mask (making it impossible to start) or unmask a socket (cups.socket)

# systemctl mask cups.socket
# systemctl unmask cups.socket

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Special services

# Restart networking
systemctl restart systemd-networkd

References

• manage-services-using-systemd-and-systemctl-in-linux