How to Manage ‘Systemd’ Services and Units Using ‘Systemctl’ in Linux

CPU Utilization (Shares) of a Service

25. Get the current CPU Shares of a Service (say httpd).

# systemctl show -p CPUShares httpd.service

CPUShares=1024

Note: The default each service has a CPUShare = 1024. You may increase/decrease the CPU share of a process.

26. Limit the CPU Share of a service (httpd.service) to 2000 CPUShares/

# systemctl set-property httpd.service CPUShares=2000
# systemctl show -p CPUShares httpd.service

CPUShares=2000

Note: When you set CPUShare for a service, a directory with the name of service is created (httpd.service.d) which contains a file 90-CPUShares.conf which contains the CPUShare Limit information. You may view the file as:

# vi /etc/systemd/system/httpd.service.d/90-CPUShares.conf 

[Service]
CPUShares=2000        

27. Check all the configuration details of a service.

# systemctl show httpd

Id=httpd.service
Names=httpd.service
Requires=basic.target
Wants=system.slice
WantedBy=multi-user.target
Conflicts=shutdown.target
Before=shutdown.target multi-user.target
After=network.target remote-fs.target nss-lookup.target systemd-journald.socket basic.target system.slice
Description=The Apache HTTP Server
LoadState=loaded
ActiveState=active
SubState=running
FragmentPath=/usr/lib/systemd/system/httpd.service
....

28. Analyze critical chain for a service (httpd).

# systemd-analyze critical-chain httpd.service

The time after the unit is active or started is printed after the "@" character.
The time the unit takes to start is printed after the "+" character.

httpd.service +142ms
└─network.target @11.168s
  └─network.service @9.456s +1.712s
    └─NetworkManager.service @8.858s +596ms
      └─firewalld.service @4.931s +3.926s
        └─basic.target @4.916s
          └─sockets.target @4.916s
            └─dbus.socket @4.916s
              └─sysinit.target @4.905s
                └─systemd-update-utmp.service @4.864s +39ms
                  └─auditd.service @4.563s +301ms
                    └─systemd-tmpfiles-setup.service @4.485s +69ms
                      └─rhel-import-state.service @4.342s +142ms
                        └─local-fs.target @4.324s
                          └─boot.mount @4.286s +31ms
                            └─[email protected]\x2duuid-79f594ad\x2da332\x2d4730\x2dbb5f\x2d85d196080964.service @4.092s +149ms
                              └─dev-disk-by\x2duuid-79f594ad\x2da332\x2d4730\x2dbb5f\x2d85d196080964.device @4.092s

29. Get a list of dependencies for a service (httpd).

# systemctl list-dependencies httpd.service

httpd.service
├─system.slice
└─basic.target
  ├─firewalld.service
  ├─microcode.service
  ├─rhel-autorelabel-mark.service
  ├─rhel-autorelabel.service
  ├─rhel-configure.service
  ├─rhel-dmesg.service
  ├─rhel-loadmodules.service
  ├─paths.target
  ├─slices.target
  │ ├─-.slice
  │ └─system.slice
  ├─sockets.target
  │ ├─dbus.socket
....

30. List control groups hierarchically.

# systemd-cgls

├─1 /usr/lib/systemd/systemd --switched-root --system --deserialize 23
├─user.slice
│ └─user-0.slice
│   └─session-1.scope
│     ├─2498 sshd: [email protected]/0    
│     ├─2500 -bash
│     ├─4521 systemd-cgls
│     └─4522 systemd-cgls
└─system.slice
  ├─httpd.service
  │ ├─4440 /usr/sbin/httpd -DFOREGROUND
  │ ├─4442 /usr/sbin/httpd -DFOREGROUND
  │ ├─4443 /usr/sbin/httpd -DFOREGROUND
  │ ├─4444 /usr/sbin/httpd -DFOREGROUND
  │ ├─4445 /usr/sbin/httpd -DFOREGROUND
  │ └─4446 /usr/sbin/httpd -DFOREGROUND
  ├─polkit.service
  │ └─721 /usr/lib/polkit-1/polkitd --no-debug
....

31. List control group according to CPU, memory, Input, and Output.

# systemd-cgtop

Path                                                              Tasks   %CPU   Memory  Input/s Output/s

/                                                                    83    1.0   437.8M        -        -
/system.slice                                                         -    0.1        -        -        -
/system.slice/mariadb.service                                         2    0.1        -        -        -
/system.slice/tuned.service                                           1    0.0        -        -        -
/system.slice/httpd.service                                           6    0.0        -        -        -
/system.slice/NetworkManager.service                                  1      -        -        -        -
/system.slice/atop.service                                            1      -        -        -        -
/system.slice/atopacct.service                                        1      -        -        -        -
/system.slice/auditd.service                                          1      -        -        -        -
/system.slice/crond.service                                           1      -        -        -        -
/system.slice/dbus.service                                            1      -        -        -        -
/system.slice/firewalld.service                                       1      -        -        -        -
/system.slice/lvm2-lvmetad.service                                    1      -        -        -        -
/system.slice/polkit.service                                          1      -        -        -        -
/system.slice/postfix.service                                         3      -        -        -        -
/system.slice/rsyslog.service                                         1      -        -        -        -
/system.slice/system-getty.slice/[email protected]                   1      -        -        -        -
/system.slice/systemd-journald.service                                1      -        -        -        -
/system.slice/systemd-logind.service                                  1      -        -        -        -
/system.slice/systemd-udevd.service                                   1      -        -        -        -
/system.slice/webmin.service                                          1      -        -        -        -
/user.slice/user-0.slice/session-1.scope                              3      -        -        -        -

Control System Runlevels

32. How to start a system rescue mode.

# systemctl rescue

Broadcast message from [email protected] on pts/0 (Wed 2015-04-29 11:31:18 IST):

The system is going down to rescue mode NOW!

33. How to enter into emergency mode.

# systemctl emergency

Welcome to emergency mode! After logging in, type "journalctl -xb" to view
system logs, "systemctl reboot" to reboot, "systemctl default" to try again
to boot into default mode.

34. List current run levels in use.

# systemctl get-default

multi-user.target

35. How to start Runlevel 5 aka graphical mode.

# systemctl isolate runlevel5.target
OR
# systemctl isolate graphical.target

36. How to start Runlevel 3 aka multiuser mode (command line).

# systemctl isolate runlevel3.target
OR
# systemctl isolate multiuser.target

36. How to set multiuser mode or graphical mode as default run level.

# systemctl set-default runlevel3.target

# systemctl set-default runlevel5.target

37. How to reboot, halt, suspend, hibernate, or put a system in hybrid-sleep.

# systemctl reboot

# systemctl halt

# systemctl suspend

# systemctl hibernate

# systemctl hybrid-sleep

For those who may not be aware of run levels and what it does.

  1. Runlevel 0 : Shut down and Power off the system.
  2. Runlevel 1 : Rescue?Maintainance Mode.
  3. Runlevel 3 : multiuser, no-graphic system.
  4. Runlevel 4 : multiuser, no-graphic system.
  5. Runlevel 5 : multiuser, graphical system.
  6. Runlevel 6 : Shutdown and Reboot the machine.

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23 thoughts on “How to Manage ‘Systemd’ Services and Units Using ‘Systemctl’ in Linux”

  1. I am just about starting with Ubuntu on Windows 10 – have tried it with WSL 2 and from Ubuntu as well.

    I started following your instructions, but couldn’t go beyond this point.

    # ps -eaf | grep [s]ystemd
    

    This returned an empty value, and hence am unable to proceed any farther. I have been stuck at this error now for weeks BUT no luck.

    I always get this error

    The system has not been booted with systemd as an init system (PID 1). Can't operate.
    Failed to create bus connection: Host is down `.
    

    I will be very thankful and appreciate a lot if someone here can bail me out of it?
    TIA

    Reply
    • From the error, it seems that the systemd is not the init system. I never used WSL but MS might not be using systems.

      Can you see systemd in the output of top command?

      Reply

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