Introduction to the Use of System CTL Tools

Keywords: socket Linux DBus RHEL

Systemctl is a system D tool, which is mainly responsible for controlling the system D system and service manager.

Systemd is a collection of system management daemons, tools, and libraries that replace the initial process of System V. Systemd's function is to centrally manage and configure UNIX-like systems.

In the Linux ecosystem, Systemd is deployed in most standard Linux distributions, and only a few have not yet been deployed. Systemd is usually the parent of all other daemons, but not always.

Using System CTL to manage Linux services

The purpose of this paper is to clarify "how to control systems and services" on systems running system D.

Systemd Initial Experience and Systemctl Foundation

1. First check if there is a system installed in your system and determine the version currently installed.

    

  1. # systemctl --version
    2. 

    3. 

  3. systemd 215
    4. 

  4. +PAM +AUDIT +SELINUX +IMA +SYSVINIT +LIBCRYPTSETUP +GCRYPT +ACL +XZ -SECCOMP -APPARMOR
    5.

As is clear from the example above, we installed the 215 version of system D.

2. Check the installation location of binary and library files for system D and system CTL

    

  1. # whereis systemd 
    2. 

  2. systemd: /usr/lib/systemd /etc/systemd /usr/share/systemd /usr/share/man/man1/systemd.1.gz
    3. 

    4. 

    5. 

  5. # whereis systemctl
    6. 

  6. systemctl: /usr/bin/systemctl /usr/share/man/man1/systemctl.1.gz
    7.

3. Check whether system D is running

    

  1. # ps -eaf | grep [s]ystemd
    2. 

    3. 

  3. root         1     0  0 16:27 ?        00:00:00 /usr/lib/systemd/systemd --switched-root --system --deserialize 23
    4. 

  4. root       444     1  0 16:27 ?        00:00:00 /usr/lib/systemd/systemd-journald
    5. 

  5. root       469     1  0 16:27 ?        00:00:00 /usr/lib/systemd/systemd-udevd
    6. 

  6. root       555     1  0 16:27 ?        00:00:00 /usr/lib/systemd/systemd-logind
    7. 

  7. dbus       556     1  0 16:27 ?        00:00:00 /bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation
    8.

Note: System D runs as a parent process (PID=1). In the ps command output with the (-e) parameter above, select all processes, (-a) select all processes except session lead, and use the (-f) parameter to output the complete format list (i.e. -eaf).

Note also the brackets that follow in the preceding example and the rest of the example. Square bracket expressions are part of grep's character class expressions.

4. Analysis of system D startup process

    

  1. # systemd-analyze
    2. 

  2. Startup finished in 487ms (kernel) + 2.776s (initrd) + 20.229s (userspace) = 23.493s
    3.

5. Analyse the time spent by each process at startup

    

  1. # systemd-analyze blame
    2. 

    3. 

  3. 8.565s mariadb.service
    4. 

  4. 7.991s webmin.service
    5. 

  5. 6.095s postfix.service
    6. 

  6. 4.311s httpd.service
    7. 

  7. 3.926s firewalld.service
    8. 

  8. 3.780s kdump.service
    9. 

  9. 3.238s tuned.service
    10. 

  10. 1.712s network.service
    11. 

  11. 1.394s lvm2-monitor.service
    12. 

  12. 1.126s systemd-logind.service
    13. 

  13. ....
    14.

6. Analysis of critical chains at startup

    

  1. # systemd-analyze critical-chain
    2. 

    3. 

  3. The time after the unit is active or started is printed after the "@" character.
    4. 

  4. The time the unit takes to start is printed after the "+" character.
    5. 

    6. 

  6. multi-user.target @20.222s
    7. 

  7. └─mariadb.service @11.657s +8.565s
    8. 

  8.   └─network.target @11.168s
    9. 

  9.     └─network.service @9.456s +1.712s
    10. 

  10.       └─NetworkManager.service @8.858s +596ms
    11. 

  11.         └─firewalld.service @4.931s +3.926s
    12. 

  12.           └─basic.target @4.916s
    13. 

  13.             └─sockets.target @4.916s
    14. 

  14.               └─dbus.socket @4.916s
    15. 

  15.                 └─sysinit.target @4.905s
    16. 

  16.                   └─systemd-update-utmp.service @4.864s +39ms
    17. 

  17.                     └─auditd.service @4.563s +301ms
    18. 

  18.                       └─systemd-tmpfiles-setup.service @4.485s +69ms
    19. 

  19.                         └─rhel-import-state.service @4.342s +142ms
    20. 

  20.                           └─local-fs.target @4.324s
    21. 

  21.                             └─boot.mount @4.286s +31ms
    22. 

  22.                               └─systemd-fsck@dev-disk-by\x2duuid-79f594ad\x2da332\x2d4730\x2dbb5f\x2d85d19608096
    23. 

  23.                                 └─dev-disk-by\x2duuid-79f594ad\x2da332\x2d4730\x2dbb5f\x2d85d196080964.device @4
    24.

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

7. List all available units

    

  1. # systemctl list-unit-files
    2. 

    3. 

  3. UNIT FILE                                   STATE   
    4. 

  4. proc-sys-fs-binfmt_misc.automount           static  
    5. 

  5. dev-hugepages.mount                         static  
    6. 

  6. dev-mqueue.mount                            static  
    7. 

  7. proc-sys-fs-binfmt_misc.mount               static  
    8. 

  8. sys-fs-fuse-connections.mount               static  
    9. 

  9. sys-kernel-config.mount                     static  
    10. 

  10. sys-kernel-debug.mount                      static  
    11. 

  11. tmp.mount                                   disabled
    12. 

  12. brandbot.path                               disabled
    13. 

  13. .....
    14.

8. List all running units

    

  1. # systemctl list-units
    2. 

    3. 

  3. UNIT                                        LOAD   ACTIVE SUB       DESCRIPTION
    4. 

  4. proc-sys-fs-binfmt_misc.automount           loaded active waiting   Arbitrary Executable File Formats File Syste
    5. 

  5. sys-devices-pc...0-1:0:0:0-block-sr0.device loaded active plugged   VBOX_CD-ROM
    6. 

  6. sys-devices-pc...:00:03.0-net-enp0s3.device loaded active plugged   PRO/1000 MT Desktop Adapter
    7. 

  7. sys-devices-pc...00:05.0-sound-card0.device loaded active plugged   82801AA AC'97 Audio Controller
    8. 

  8. sys-devices-pc...:0:0-block-sda-sda1.device loaded active plugged   VBOX_HARDDISK
    9. 

  9. sys-devices-pc...:0:0-block-sda-sda2.device loaded active plugged   LVM PV Qzyo3l-qYaL-uRUa-Cjuk-pljo-qKtX-VgBQ8
    10. 

  10. sys-devices-pc...0-2:0:0:0-block-sda.device loaded active plugged   VBOX_HARDDISK
    11. 

  11. sys-devices-pl...erial8250-tty-ttyS0.device loaded active plugged   /sys/devices/platform/serial8250/tty/ttyS0
    12. 

  12. sys-devices-pl...erial8250-tty-ttyS1.device loaded active plugged   /sys/devices/platform/serial8250/tty/ttyS1
    13. 

  13. sys-devices-pl...erial8250-tty-ttyS2.device loaded active plugged   /sys/devices/platform/serial8250/tty/ttyS2
    14. 

  14. sys-devices-pl...erial8250-tty-ttyS3.device loaded active plugged   /sys/devices/platform/serial8250/tty/ttyS3
    15. 

  15. sys-devices-virtual-block-dm\x2d0.device    loaded active plugged   /sys/devices/virtual/block/dm-0
    16. 

  16. sys-devices-virtual-block-dm\x2d1.device    loaded active plugged   /sys/devices/virtual/block/dm-1
    17. 

  17. sys-module-configfs.device                  loaded active plugged   /sys/module/configfs
    18. 

  18. ...
    19.

9. List all failure units

    

  1. # systemctl --failed
    2. 

    3. 

  3. UNIT          LOAD   ACTIVE SUB    DESCRIPTION
    4. 

  4. kdump.service loaded failed failed Crash recovery kernel arming
    5. 

    6. 

  6. LOAD   = Reflects whether the unit definition was properly loaded.
    7. 

  7. ACTIVE = The high-level unit activation state, i.e. generalization of SUB.
    8. 

  8. SUB    = The low-level unit activation state, values depend on unit type.
    9. 

    10. 

  10. 1 loaded units listed. Pass --all to see loaded but inactive units, too.
    11. 

  11. To show all installed unit files use 'systemctl list-unit-files'.
    12.

10. Check whether a unit, such as cron.service, is enabled

    

  1. # systemctl is-enabled crond.service
    2. 

    3. 

  3. enabled
    4.

11. Check whether a unit or service is running

    

  1. # systemctl status firewalld.service
    2. 

    3. 

  3. firewalld.service - firewalld - dynamic firewall daemon
    4. 

  4.    Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled)
    5. 

  5.    Active: active (running) since Tue 2015-04-28 16:27:55 IST; 34min ago
    6. 

  6.  Main PID: 549 (firewalld)
    7. 

  7.    CGroup: /system.slice/firewalld.service
    8. 

  8.            └─549 /usr/bin/python -Es /usr/sbin/firewalld --nofork --nopid
    9. 

    10. 

  10. Apr 28 16:27:51 tecmint systemd[1]: Starting firewalld - dynamic firewall daemon...
    11. 

  11. Apr 28 16:27:55 tecmint systemd[1]: Started firewalld - dynamic firewall daemon.
    12.

Using System CTL to control and manage services

12. List all services (including enabled and disabled)

    

  1. # systemctl list-unit-files --type=service
    2. 

    3. 

  3. UNIT FILE                                   STATE   
    4. 

  4. arp-ethers.service                          disabled
    5. 

  5. auditd.service                              enabled 
    6. 

  6. autovt@.service                             disabled
    7. 

  7. blk-availability.service                    disabled
    8. 

  8. brandbot.service                            static  
    9. 

  9. collectd.service                            disabled
    10. 

  10. console-getty.service                       disabled
    11. 

  11. console-shell.service                       disabled
    12. 

  12. cpupower.service                            disabled
    13. 

  13. crond.service                               enabled 
    14. 

  14. dbus-org.fedoraproject.FirewallD1.service   enabled 
    15. 

  15. ....
    16.

13. How to start, restart, stop, overload services and check the status of services (such as httpd.service) in Linux

    

  1. # systemctl start httpd.service
    2. 

  2. # systemctl restart httpd.service
    3. 

  3. # systemctl stop httpd.service
    4. 

  4. # systemctl reload httpd.service
    5. 

  5. # systemctl status httpd.service
    6. 

    7. 

  7. httpd.service - The Apache HTTP Server
    8. 

  8.    Loaded: loaded (/usr/lib/systemd/system/httpd.service; enabled)
    9. 

  9.    Active: active (running) since Tue 2015-04-28 17:21:30 IST; 6s ago
    10. 

  10.   Process: 2876 ExecStop=/bin/kill -WINCH ${MAINPID} (code=exited, status=0/SUCCESS)
    11. 

  11.  Main PID: 2881 (httpd)
    12. 

  12.    Status: "Processing requests..."
    13. 

  13.    CGroup: /system.slice/httpd.service
    14. 

  14.            ├─2881 /usr/sbin/httpd -DFOREGROUND
    15. 

  15.            ├─2884 /usr/sbin/httpd -DFOREGROUND
    16. 

  16.            ├─2885 /usr/sbin/httpd -DFOREGROUND
    17. 

  17.            ├─2886 /usr/sbin/httpd -DFOREGROUND
    18. 

  18.            ├─2887 /usr/sbin/httpd -DFOREGROUND
    19. 

  19.            └─2888 /usr/sbin/httpd -DFOREGROUND
    20. 

    21. 

  21. Apr 28 17:21:30 tecmint systemd[1]: Starting The Apache HTTP Server...
    22. 

  22. Apr 28 17:21:30 tecmint httpd[2881]: AH00558: httpd: Could not reliably determine the server's fully q...ssage
    23. 

  23. Apr 28 17:21:30 tecmint systemd[1]: Started The Apache HTTP Server.
    24. 

  24. Hint: Some lines were ellipsized, use -l to show in full.
    25.

Note: When we use the start, restart, stop and reload commands of system ctl, we will not get any output from the terminal, only the status command can print out.

14. How to activate the service and enable or disable it at startup (i.e., automatically start the service at system startup)

    

  1. # systemctl is-active httpd.service
    2. 

  2. # systemctl enable httpd.service
    3. 

  3. # systemctl disable httpd.service
    4.

15. How to block (make it unable to start) or display services (such as httpd.service)

    

  1. # systemctl mask httpd.service
    2. 

  2. ln -s '/dev/null' '/etc/systemd/system/httpd.service'
    3. 

    4. 

  4. # systemctl unmask httpd.service
    5. 

  5. rm '/etc/systemd/system/httpd.service'
    6.

16. Kill the service using the system CTL command

    

  1. # systemctl kill httpd
    2. 

  2. # systemctl status httpd
    3. 

    4. 

  4. httpd.service - The Apache HTTP Server
    5. 

  5.    Loaded: loaded (/usr/lib/systemd/system/httpd.service; enabled)
    6. 

  6.    Active: failed (Result: exit-code) since Tue 2015-04-28 18:01:42 IST; 28min ago
    7. 

  7.  Main PID: 2881 (code=exited, status=0/SUCCESS)
    8. 

  8.    Status: "Total requests: 0; Current requests/sec: 0; Current traffic:   0 B/sec"
    9. 

    10. 

  10. Apr 28 17:37:29 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.
    11. 

  11. Apr 28 17:37:29 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.
    12. 

  12. Apr 28 17:37:39 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.
    13. 

  13. Apr 28 17:37:39 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.
    14. 

  14. Apr 28 17:37:49 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.
    15. 

  15. Apr 28 17:37:49 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.
    16. 

  16. Apr 28 17:37:59 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.
    17. 

  17. Apr 28 17:37:59 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.
    18. 

  18. Apr 28 18:01:42 tecmint systemd[1]: httpd.service: control process exited, code=exited status=226
    19. 

  19. Apr 28 18:01:42 tecmint systemd[1]: Unit httpd.service entered failed state.
    20. 

  20. Hint: Some lines were ellipsized, use -l to show in full.
    21.

Using System CTL to control and manage mount points

17. List all system mount points

    

  1. # systemctl list-unit-files --type=mount
    2. 

    3. 

  3. UNIT FILE                     STATE   
    4. 

  4. dev-hugepages.mount           static  
    5. 

  5. dev-mqueue.mount              static  
    6. 

  6. proc-sys-fs-binfmt_misc.mount static  
    7. 

  7. sys-fs-fuse-connections.mount static  
    8. 

  8. sys-kernel-config.mount       static  
    9. 

  9. sys-kernel-debug.mount        static  
    10. 

  10. tmp.mount                     disabled
    11.

18. Mount, unload, reload, overload system mount point and check the status of mount point in system

    

  1. # systemctl start tmp.mount
    2. 

  2. # systemctl stop tmp.mount
    3. 

  3. # systemctl restart tmp.mount
    4. 

  4. # systemctl reload tmp.mount
    5. 

  5. # systemctl status tmp.mount
    6. 

    7. 

  7. tmp.mount - Temporary Directory
    8. 

  8.    Loaded: loaded (/usr/lib/systemd/system/tmp.mount; disabled)
    9. 

  9.    Active: active (mounted) since Tue 2015-04-28 17:46:06 IST; 2min 48s ago
    10. 

  10.     Where: /tmp
    11. 

  11.      What: tmpfs
    12. 

  12.      Docs: man:hier(7)
    13. 

    14. 

  14. http://www.freedesktop.org/wiki/Software/systemd/APIFileSystems
    15. 

    16. 

  16.   Process: 3908 ExecMount=/bin/mount tmpfs /tmp -t tmpfs -o mode=1777,strictatime (code=exited, status=0/SUCCESS)
    17. 

    18. 

  18. Apr 28 17:46:06 tecmint systemd[1]: Mounting Temporary Directory...
    19. 

  19. Apr 28 17:46:06 tecmint systemd[1]: tmp.mount: Directory /tmp to mount over is not empty, mounting anyway.
    20. 

  20. Apr 28 17:46:06 tecmint systemd[1]: Mounted Temporary Directory.
    21.

19. Activate, enable, or disable mount points at startup (automatic mount at system startup)

    

  1. # systemctl is-active tmp.mount
    2. 

  2. # systemctl enable tmp.mount
    3. 

  3. # systemctl disable  tmp.mount
    4.

20. Shield (make it unavailable) or visible mount points in Linux

    

  1. # systemctl mask tmp.mount
    2. 

    3. 

  3. ln -s '/dev/null' '/etc/systemd/system/tmp.mount'
    4. 

    5. 

  5. # systemctl unmask tmp.mount
    6. 

    7. 

  7. rm '/etc/systemd/system/tmp.mount'
    8.

Using System CTL to control and manage socket interfaces

21. List all available system socket interfaces

    

  1. # systemctl list-unit-files --type=socket
    2. 

    3. 

  3. UNIT FILE                    STATE   
    4. 

  4. dbus.socket                  static  
    5. 

  5. dm-event.socket              enabled 
    6. 

  6. lvm2-lvmetad.socket          enabled 
    7. 

  7. rsyncd.socket                disabled
    8. 

  8. sshd.socket                  disabled
    9. 

  9. syslog.socket                static  
    10. 

  10. systemd-initctl.socket       static  
    11. 

  11. systemd-journald.socket      static  
    12. 

  12. systemd-shutdownd.socket     static  
    13. 

  13. systemd-udevd-control.socket static  
    14. 

  14. systemd-udevd-kernel.socket  static  
    15. 

    16. 

  16. 11 unit files listed.
    17.

22. Start, restart, stop, overload the socket interface in Linux and check its status

    

  1. # systemctl start cups.socket
    2. 

  2. # systemctl restart cups.socket
    3. 

  3. # systemctl stop cups.socket
    4. 

  4. # systemctl reload cups.socket
    5. 

  5. # systemctl status cups.socket
    6. 

    7. 

  7. cups.socket - CUPS Printing Service Sockets
    8. 

  8.    Loaded: loaded (/usr/lib/systemd/system/cups.socket; enabled)
    9. 

  9.    Active: active (listening) since Tue 2015-04-28 18:10:59 IST; 8s ago
    10. 

  10.    Listen: /var/run/cups/cups.sock (Stream)
    11. 

    12. 

  12. Apr 28 18:10:59 tecmint systemd[1]: Starting CUPS Printing Service Sockets.
    13. 

  13. Apr 28 18:10:59 tecmint systemd[1]: Listening on CUPS Printing Service Sockets.
    14.

23. Activate the socket interface at startup and enable or disable it (self-startup at system startup)

    

  1. # systemctl is-active cups.socket
    2. 

  2. # systemctl enable cups.socket
    3. 

  3. # systemctl disable cups.socket
    4.

24. Shield (make it unable to start) or display socket interface

    

  1. # systemctl mask cups.socket
    2. 

  2. ln -s '/dev/null' '/etc/systemd/system/cups.socket'
    3. 

    4. 

  4. # systemctl unmask cups.socket
    5. 

  5. rm '/etc/systemd/system/cups.socket'
    6.

CPU utilization of services (allocation)

25. Get the current CPU allocation for a service (such as httpd)

    

  1. # systemctl show -p CPUShares httpd.service
    2. 

    3. 

  3. CPUShares=1024
    4.

Note: The default CPU allocation for each service = 1024, you can increase or decrease the CPU allocation for a process.

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

    

  1. # systemctl set-property httpd.service CPUShares=2000
    2. 

  2. # systemctl show -p CPUShares httpd.service
    3. 

    4. 

  4. CPUShares=2000
    5.

Note: When you set CPUShares for a service, you automatically create a directory named after the service name (such as httpd.service), which contains a file named 90-CPUShares.conf, which contains CPUShare restriction information. You can view the file as follows:

    

  1. # vi /etc/systemd/system/httpd.service.d/90-CPUShares.conf 
    2. 

    3. 

  3. [Service]
    4. 

  4. CPUShares=2000        
    5.

27. Check all configuration details of a service

    

  1. # systemctl show httpd
    2. 

    3. 

  3. Id=httpd.service
    4. 

  4. Names=httpd.service
    5. 

  5. Requires=basic.target
    6. 

  6. Wants=system.slice
    7. 

  7. WantedBy=multi-user.target
    8. 

  8. Conflicts=shutdown.target
    9. 

  9. Before=shutdown.target multi-user.target
    10. 

  10. After=network.target remote-fs.target nss-lookup.target systemd-journald.socket basic.target system.slice
    11. 

  11. Description=The Apache HTTP Server
    12. 

  12. LoadState=loaded
    13. 

  13. ActiveState=active
    14. 

  14. SubState=running
    15. 

  15. FragmentPath=/usr/lib/systemd/system/httpd.service
    16. 

  16. ....
    17.

28. Analyzing the key chains of a service (httpd)

    

  1. # systemd-analyze critical-chain httpd.service
    2. 

    3. 

  3. The time after the unit is active or started is printed after the "@" character.
    4. 

  4. The time the unit takes to start is printed after the "+" character.
    5. 

    6. 

  6. httpd.service +142ms
    7. 

  7. └─network.target @11.168s
    8. 

  8.   └─network.service @9.456s +1.712s
    9. 

  9.     └─NetworkManager.service @8.858s +596ms
    10. 

  10.       └─firewalld.service @4.931s +3.926s
    11. 

  11.         └─basic.target @4.916s
    12. 

  12.           └─sockets.target @4.916s
    13. 

  13.             └─dbus.socket @4.916s
    14. 

  14.               └─sysinit.target @4.905s
    15. 

  15.                 └─systemd-update-utmp.service @4.864s +39ms
    16. 

  16.                   └─auditd.service @4.563s +301ms
    17. 

  17.                     └─systemd-tmpfiles-setup.service @4.485s +69ms
    18. 

  18.                       └─rhel-import-state.service @4.342s +142ms
    19. 

  19.                         └─local-fs.target @4.324s
    20. 

  20.                           └─boot.mount @4.286s +31ms
    21. 

  21.                             └─systemd-fsck@dev-disk-by\x2duuid-79f594ad\x2da332\x2d4730\x2dbb5f\x2d85d196080964.service @4.092s +149ms
    22. 

  22.                               └─dev-disk-by\x2duuid-79f594ad\x2da332\x2d4730\x2dbb5f\x2d85d196080964.device @4.092s
    23.

29. Get a dependency list for a service (httpd)

    

  1. # systemctl list-dependencies httpd.service
    2. 

    3. 

  3. httpd.service
    4. 

  4. ├─system.slice
    5. 

  5. └─basic.target
    6. 

  6.   ├─firewalld.service
    7. 

  7.   ├─microcode.service
    8. 

  8.   ├─rhel-autorelabel-mark.service
    9. 

  9.   ├─rhel-autorelabel.service
    10. 

  10.   ├─rhel-configure.service
    11. 

  11.   ├─rhel-dmesg.service
    12. 

  12.   ├─rhel-loadmodules.service
    13. 

  13.   ├─paths.target
    14. 

  14.   ├─slices.target
    15. 

  15.   │ ├─-.slice
    16. 

  16.   │ └─system.slice
    17. 

  17.   ├─sockets.target
    18. 

  18.   │ ├─dbus.socket
    19. 

  19. ....
    20.

30. List control groups by level

    

  1. # systemd-cgls
    2. 

    3. 

  3. ├─1 /usr/lib/systemd/systemd --switched-root --system --deserialize 23
    4. 

  4. ├─user.slice
    5. 

  5. │ └─user-0.slice
    6. 

  6. │   └─session-1.scope
    7. 

  7. │     ├─2498 sshd: root@pts/0    
    8. 

  8. │     ├─2500 -bash
    9. 

  9. │     ├─4521 systemd-cgls
    10. 

  10. │     └─4522 systemd-cgls
    11. 

  11. └─system.slice
    12. 

  12.   ├─httpd.service
    13. 

  13.   │ ├─4440 /usr/sbin/httpd -DFOREGROUND
    14. 

  14.   │ ├─4442 /usr/sbin/httpd -DFOREGROUND
    15. 

  15.   │ ├─4443 /usr/sbin/httpd -DFOREGROUND
    16. 

  16.   │ ├─4444 /usr/sbin/httpd -DFOREGROUND
    17. 

  17.   │ ├─4445 /usr/sbin/httpd -DFOREGROUND
    18. 

  18.   │ └─4446 /usr/sbin/httpd -DFOREGROUND
    19. 

  19.   ├─polkit.service
    20. 

  20.   │ └─721 /usr/lib/polkit-1/polkitd --no-debug
    21. 

  21. ....
    22.

31. List control groups by CPU, memory, input and output

    

  1. # systemd-cgtop
    2. 

    3. 

  3. Path                                                              Tasks   %CPU   Memory  Input/s Output/s
    4. 

    5. 

  5. /                                                                    83    1.0   437.8M        -        -
    6. 

  6. /system.slice                                                         -    0.1        -        -        -
    7. 

  7. /system.slice/mariadb.service                                         2    0.1        -        -        -
    8. 

  8. /system.slice/tuned.service                                           1    0.0        -        -        -
    9. 

  9. /system.slice/httpd.service                                           6    0.0        -        -        -
    10. 

  10. /system.slice/NetworkManager.service                                  1      -        -        -        -
    11. 

  11. /system.slice/atop.service                                            1      -        -        -        -
    12. 

  12. /system.slice/atopacct.service                                        1      -        -        -        -
    13. 

  13. /system.slice/auditd.service                                          1      -        -        -        -
    14. 

  14. /system.slice/crond.service                                           1      -        -        -        -
    15. 

  15. /system.slice/dbus.service                                            1      -        -        -        -
    16. 

  16. /system.slice/firewalld.service                                       1      -        -        -        -
    17. 

  17. /system.slice/lvm2-lvmetad.service                                    1      -        -        -        -
    18. 

  18. /system.slice/polkit.service                                          1      -        -        -        -
    19. 

  19. /system.slice/postfix.service                                         3      -        -        -        -
    20. 

  20. /system.slice/rsyslog.service                                         1      -        -        -        -
    21. 

  21. /system.slice/system-getty.slice/getty@tty1.service                   1      -        -        -        -
    22. 

  22. /system.slice/systemd-journald.service                                1      -        -        -        -
    23. 

  23. /system.slice/systemd-logind.service                                  1      -        -        -        -
    24. 

  24. /system.slice/systemd-udevd.service                                   1      -        -        -        -
    25. 

  25. /system.slice/webmin.service                                          1      -        -        -        -
    26. 

  26. /user.slice/user-0.slice/session-1.scope                              3      -        -        -        -
    27.

Operational Level of Control System

32. Start-up system rescue mode

    

  1. # systemctl rescue
    2. 

    3. 

  3. Broadcast message from root@tecmint on pts/0 (Wed 2015-04-29 11:31:18 IST):
    4. 

    5. 

  5. The system is going down to rescue mode NOW!
    6.

33. Enter Emergency Mode

    

  1. # systemctl emergency
    2. 

    3. 

  3. Welcome to emergency mode! After logging in, type "journalctl -xb" to view
    4. 

  4. system logs, "systemctl reboot" to reboot, "systemctl default" to try again
    5. 

  5. to boot into default mode.
    6.

34. List the current operational levels used

    

  1. # systemctl get-default
    2. 

    3. 

  3. multi-user.target
    4.

35. Start-up operation level 5, i.e. graphical mode

    

  1. # systemctl isolate runlevel5.target
    2. 

  2. or
    3. 

  3. # systemctl isolate graphical.target
    4.

36. Start Run Level 3, Multiuser Mode (Command Line)

    

  1. # systemctl isolate runlevel3.target
    2. 

  2. or
    3. 

  3. # systemctl isolate multiuser.target
    4.

36. Set multiuser mode or graphical mode to default runtime level

    

  1. # systemctl set-default runlevel3.target
    2. 

    3. 

  3. # systemctl set-default runlevel5.target
    4.

37. Restart, stop, hang, hibernate or put the system into mixed sleep

    

  1. # systemctl reboot
    2. 

    3. 

  3. # systemctl halt
    4. 

    5. 

  5. # systemctl suspend
    6. 

    7. 

  7. # systemctl hibernate
    8. 

    9. 

  9. # systemctl hybrid-sleep
    10.

For those who do not know the operation level, the following is explained.

  • Runlevel 0: Shut down the system
  • Runlevel 1: Rescue? maintenance mode
  • Runlevel 3: Multi-user, Graphic-free System
  • Runlevel 4: Multi-user, Graphic-free System
  • Runlevel 5: Multiuser, Graphical System
  • Runlevel 6: Close and restart the machine

Let's call it a day. Keep in touch and comment. Don't forget to give us some valuable feedback in the comments below. Like us, share with us, seek diffusion.

via: http://www.tecmint.com/manage-services-using-systemd-and-systemctl-in-linux/

Author: Avishek Kumar Translator: GOLinux Proofreading: wxy

This article is composed of LCTT Original translation, Linux China Honorary launch

Compile from: http://www.tecmint.com/manage-services-using-systemd-and-systemctl-in-linux/ Author: Avishek Kumar
Original: LCTT https://linux.cn/article-5926-1.html Translator: GOLinux

This article is originally translated by LCTT. Linux launched in China . Want to join the ranks of translators and make some contributions to open source? Welcome to join LCTT!
Translation work and translation publication are for learning and communication purposes only, and translation work shall comply with these requirements. CC-BY-NC-SA Agreement Provisions If our work encroaches on your rights and interests, please contact us in time.
Welcome to comply. CC-BY-NC-SA Agreement Provisions Reproduced, please mark and retain the original/translation links and author/translator information in the text.  
The article only represents the author's knowledge and opinions. If you have different opinions, please queue downstairs.Make complaints :D 

Posted by Yucky on Fri, 24 May 2019 15:33:34 -0700

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