How to Manage 'Systemd' Services and Units Using 'Systemctl' in Linux - Part 2
Abstract: /system.slice/dbus.service 1 - - - -/system.slice/httpd.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.
- Runlevel 0 : Shut down and Power off the system.
- Runlevel 1 : Rescue?Maintainance Mode.
- Runlevel 3 : multiuser, no-graphic system.
- Runlevel 4 : multiuser, no-graphic system.
- Runlevel 5 : multiuser, graphical system.
- Runlevel 6 : Shutdown and Reboot the machine.
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