systemctl命令是系統服務管理器指令，主要負責控制systemd系統和服務管理器，它實際上將 service 和 chkconfig 這兩個命令組合到一起。
CentOS 7.x開始，CentOS開始使用systemd服務來代替daemon，原來管理系統啟動和管理系統服務的相關命令全部由systemctl命令來代替。
Systemd是一個系統管理守護進程、工具和庫的集合，用於取代System V初始進程。Systemd的功能是用於集中管理和配置類UNIX系統。
在Linux生態系統中，Systemd被部署到了大多數的標准Linux發行版中，只有為數不多的幾個發行版尚未部署。Systemd通常是所有其它守護進程的父進程，但並非全是如此。
1、原來的 service 命令與 systemctl 命令對比
| daemon命令 | systemctl命令 | 說明 |
|---|---|---|
| service [服務] start | systemctl start [unit type] | 啟動服務 |
| service [服務] stop | systemctl stop [unit type] | 停止服務 |
| service [服務] restart | systemctl restart [unit type] | 重啟服務 |
此外還是二個systemctl參數沒有與service命令參數對應
- status：參數來查看服務運行情況
- reload：重新加載服務，加載更新后的配置文件（並不是所有服務都支持這個參數，比如network.service）
示例：
#啟動網絡服務
systemctl start network.service
#停止網絡服務
systemctl stop network.service
#重啟網絡服務
systemctl restart network.service
#查看網絡服務狀態
systemctl status network.serivce
2、原來的chkconfig 命令與 systemctl 命令對比
| daemon命令 | systemctl命令 | 說明 |
|---|---|---|
| chkconfig [服務] on | systemctl enable [unit type] | 設置服務開機啟動 |
| chkconfig [服務] off | systemctl disable [unit type] | 設備服務禁止開機啟動 |
示例：
#停止cup電源管理服務
systemctl stop cups.service
#禁止cups服務開機啟動
systemctl disable cups.service
#查看cups服務狀態
systemctl status cups.service
#重新設置cups服務開機啟動
systemctl enable cups.service
3、查看系統上上所有的服務
命令格式：systemctl [command] [–type=TYPE] [–all]
參數詳解：
command - list-units：依據unit列出所有啟動的unit。加上 –all 才會列出沒啟動的unit; - list-unit-files:依據/usr/lib/systemd/system/ 內的啟動文件，列出啟動文件列表
–type=TYPE - 為unit type, 主要有service, socket, target
應用舉例：
| systemctl命令 | 說明 |
|---|---|
| systemctl | 列出所有的系統服務 |
| systemctl list-units | 列出所有啟動unit |
| systemctl list-unit-files | 列出所有啟動文件 |
| systemctl list-units –type=service –all | 列出所有service類型的unit |
| systemctl list-units –type=service –all grep cpu | 列出 cpu電源管理機制的服務 |
| systemctl list-units –type=target –all | 列出所有target |
4、systemctl特殊的用法
| systemctl命令 | 說明 |
|---|---|
| systemctl is-active [unit type] | 查看服務是否運行 |
| systemctl is-enable [unit type] | 查看服務是否設置為開機啟動 |
| systemctl mask [unit type] | 注銷指定服務 |
| systemctl unmask [unit type] | 取消注銷指定服務 |
應用舉例：
#查看網絡服務是否啟動 systemctl is-active network.service #檢查網絡服務是否設置為開機啟動 systemctl is-enable network.service #停止cups服務 systemctl stop cups.service #注銷cups服務 systemctl mask cups.service #查看cups服務狀態 systemctl status cups.service #取消注銷cups服務 systemctl unmask cups.service
5、常用示例：
Systemctl基礎、體驗
1. 檢查系統中是否安裝有systemctl並確定當前安裝的版本
[root@CTU1000094955 ~]# systemctl --version systemd 219 +PAM +AUDIT +SELINUX +IMA -APPARMOR +SMACK +SYSVINIT +UTMP +LIBCRYPTSETUP +GCRYPT +GNUTLS +ACL +XZ -LZ4 -SECCOMP +BLKID +ELFUTILS +KMOD +IDN
上例中很清楚地表明，我們安裝了219版本的systemctl。
2. 檢查systemd和systemctl的二進制文件和庫文件的安裝位置
[root@CTU1000094955 ~]# whereis systemd systemd: /usr/lib/systemd /etc/systemd /usr/share/systemd /usr/share/man/man1/systemd.1.gz [root@CTU1000094955 ~]# whereis systemctl systemctl: /usr/bin/systemctl /usr/share/man/man1/systemctl.1.gz
3. 檢查systemd是否運行
[root@CTU1000094955 ~]# ps -eaf | grep [s]ystemd root 1 0 0 16:15 ? 00:00:04 /usr/lib/systemd/systemd --switched-root --system --deserialize 21 root 631 1 0 16:15 ? 00:00:24 /usr/lib/systemd/systemd-journald root 661 1 0 16:15 ? 00:00:00 /usr/lib/systemd/systemd-udevd dbus 813 1 0 16:15 ? 00:00:02 /bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation root 841 1 0 16:15 ? 00:00:00 /usr/lib/systemd/systemd-logind
注意：systemd是作為父進程（PID=1）運行的。在上面帶（-e）參數的ps命令輸出中，選擇所有進程，（-a）選擇除會話前導外的所有進程，並使用（-f）參數輸出完整格式列表（即 -eaf）。
也請注意上例中后隨的方括號和例子中剩余部分。方括號表達式是grep的字符類表達式的一部分。
4. 分析systemd啟動進程
[root@CTU1000094955 ~]# systemd-analyze Startup finished in 743ms (kernel) + 6.959s (initrd) + 17.696s (userspace) = 25.399s
5. 分析啟動時各個進程花費的時間
[root@CTU1000094955 ~]# systemd-analyze blame 11.859s dev-xvda1.device 5.670s NetworkManager-wait-online.service 4.610s plymouth-quit-wait.service 3.757s systemd-udev-settle.service 3.078s kdump.service 2.257s mysql.service 1.451s libvirtd.service 1.228s postfix.service 751ms uvp-monitor.service 675ms spesserviced.service 675ms messageserviced.service 660ms tuned.service 586ms network.service 525ms accounts-daemon.service 467ms NetworkManager.service 457ms systemd-udevd.service 416ms abrt-ccpp.service 397ms firewalld.service 365ms ModemManager.service
6. 分析啟動時的關鍵鏈
[root@CTU1000094955 ~]# systemd-analyze critical-chain 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. graphical.target @17.682s ?..multi-user.target @17.682s ?..getty.target @17.682s ?..serial-getty@hvc0.service @17.681s ?..systemd-user-sessions.service @12.929s +18ms ?..remote-fs.target @12.921s ?..remote-fs-pre.target @12.921s ?..iscsi-shutdown.service @12.907s +12ms ?..network.target @12.900s ?..network.service @12.311s +586ms ?..NetworkManager.service @6.166s +467ms ?..basic.target @5.903s ?..sockets.target @5.903s ?..rpcbind.socket @5.903s ?..sysinit.target @5.895s ?..systemd-update-utmp.service @5.877s +16ms ?..auditd.service @5.738s +135ms ?..systemd-tmpfiles-setup.service @5.661s +73ms ?..rhel-import-state.service @5.526s +134ms ?..local-fs.target @5.525s ?..run-user-0.mount @14.041s ?..local-fs-pre.target @1.615s ?..systemd-tmpfiles-setup-dev.service @ ?..kmod-static-nodes.service @1.473s ?..systemd-journald.socket ?..-.slice
重要：Systemctl接受服務（.service），掛載點（.mount），套接口（.socket）和設備（.device）作為單元。
7. 列出所有可用單元
[root@CTU1000094955 ~]# systemctl list-unit-files UNIT FILE STATE proc-sys-fs-binfmt_misc.automount static dev-hugepages.mount static dev-mqueue.mount static proc-fs-nfsd.mount static proc-sys-fs-binfmt_misc.mount static sys-fs-fuse-connections.mount static sys-kernel-config.mount static sys-kernel-debug.mount static tmp.mount disabled var-lib-nfs-rpc_pipefs.mount static brandbot.path disabled cups.path enabled systemd-ask-password-console.path static
8. 列出所有運行中單元
[root@CTU1000094955 ~]# systemctl list-units UNIT LOAD ACTIVE SUB DESCRIPTION proc-sys-fs-binfmt_misc.automount loaded active waiting Arbitrary Executable File Formats File System Automount Point sys-devices-pci0000:00-0000:00:01.1-ata2-host1-target1:0:1-1:0:1:0-block-sr0.device loaded active plugged QEMU_DVD-ROM sys-devices-platform-serial8250-tty-ttyS2.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS2 sys-devices-platform-serial8250-tty-ttyS3.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS3 sys-devices-pnp0-00:08-tty-ttyS0.device loaded active plugged /sys/devices/pnp0/00:08/tty/ttyS0 sys-devices-pnp0-00:09-tty-ttyS1.device loaded active plugged /sys/devices/pnp0/00:09/tty/ttyS1 sys-devices-vbd\x2d51712-block-xvda-xvda1.device loaded active plugged /sys/devices/vbd-51712/block/xvda/xvda1 sys-devices-vbd\x2d51712-block-xvda-xvda2.device loaded active plugged /sys/devices/vbd-51712/block/xvda/xvda2 sys-devices-vbd\x2d51712-block-xvda.device loaded active plugged /sys/devices/vbd-51712/block/xvda sys-devices-vbd\x2d51776-block-xvde.device loaded active plugged LVM PV I2rhCm-www3-J79i-r3ei-1XCb-a1qS-3OWSg9 on /dev/xvde sys-devices-vif\x2d0-net-eth0.device loaded active plugged /sys/devices/vif-0/net/eth0
9. 列出所有失敗單元
[root@CTU1000094955 ~]# systemctl --failed UNIT LOAD ACTIVE SUB DESCRIPTION ?.bluetooth.service loaded failed failed Bluetooth service ?.rc-local.service loaded failed failed /etc/rc.d/rc.local Compatibility 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. 2 loaded units listed. Pass --all to see loaded but inactive units, too. To show all installed unit files use 'systemctl list-unit-files'.
10. 檢查某個單元（如 cron.service）是否啟用
[root@CTU1000094955 ~]# systemctl is-enabled firewalld.service
disabled
11. 檢查某個單元或服務是否運行
[root@CTU1000094955 ~]# systemctl status firewalld.service ?.firewalld.service - firewalld - dynamic firewall daemon Loaded: loaded (/usr/lib/systemd/system/firewalld.service; disabled; vendor preset: enabled) Active: active (running) since Sat 2017-11-25 16:20:44 CST; 1h 29min ago Main PID: 7677 (firewalld) CGroup: /system.slice/firewalld.service ?..7677 /usr/bin/python -Es /usr/sbin/firewalld --nofork --nopid Nov 25 16:20:43 CTU1000094955 systemd[1]: Starting firewalld - dynamic firewall daemon... Nov 25 16:20:44 CTU1000094955 systemd[1]: Started firewalld - dynamic firewall daemon.
使用Systemctl控制並管理服務
12. 列出所有服務（包括啟用的和禁用的）
[root@CTU1000094955 ~]# systemctl list-unit-files --type=service UNIT FILE STATE abrt-ccpp.service enabled abrt-oops.service enabled abrt-pstoreoops.service disabled abrt-vmcore.service enabled abrt-xorg.service enabled abrtd.service enabled accounts-daemon.service enabled alsa-restore.service static alsa-state.service static alsa-store.service static anaconda-direct.service static anaconda-nm-config.service static anaconda-noshell.service static anaconda-shell@.service static
13. Linux中如何啟動、重啟、停止、重載服務以及檢查服務（如 firewalld.service）狀態
[root@CTU1000094955 ~]# systemctl start httpd.service Failed to start httpd.service: Unit httpd.service failed to load: No such file or directory. [root@CTU1000094955 ~]# systemctl start firewalld.service [root@CTU1000094955 ~]# systemctl restart firewalld.service [root@CTU1000094955 ~]# systemctl stop firewalld.service [root@CTU1000094955 ~]# systemctl reload firewalld.service Job for firewalld.service invalid. [root@CTU1000094955 ~]# systemctl status firewalld.service ?.firewalld.service - firewalld - dynamic firewall daemon Loaded: loaded (/usr/lib/systemd/system/firewalld.service; disabled; vendor preset: enabled) Active: inactive (dead) Nov 25 16:18:11 CTU1000094955 systemd[1]: Stopped firewalld - dynamic firewall daemon. Nov 25 16:20:43 CTU1000094955 systemd[1]: Starting firewalld - dynamic firewall daemon... Nov 25 16:20:44 CTU1000094955 systemd[1]: Started firewalld - dynamic firewall daemon. Nov 25 17:52:25 CTU1000094955 systemd[1]: Started firewalld - dynamic firewall daemon. Nov 25 17:52:38 CTU1000094955 systemd[1]: Stopping firewalld - dynamic firewall daemon... Nov 25 17:52:40 CTU1000094955 systemd[1]: Starting firewalld - dynamic firewall daemon... Nov 25 17:52:40 CTU1000094955 systemd[1]: Started firewalld - dynamic firewall daemon. Nov 25 17:52:53 CTU1000094955 systemd[1]: Stopping firewalld - dynamic firewall daemon... Nov 25 17:52:55 CTU1000094955 systemd[1]: Stopped firewalld - dynamic firewall daemon. Nov 25 17:53:07 CTU1000094955 systemd[1]: Unit firewalld.service cannot be reloaded because it is inactive. [root@CTU1000094955 ~]# systemctl restart firewalld.service [root@CTU1000094955 ~]# systemctl reload firewalld.service [root@CTU1000094955 ~]# systemctl status firewalld.service ?.firewalld.service - firewalld - dynamic firewall daemon Loaded: loaded (/usr/lib/systemd/system/firewalld.service; disabled; vendor preset: enabled) Active: active (running) since Sat 2017-11-25 17:53:40 CST; 8s ago Process: 31721 ExecReload=/bin/kill -HUP $MAINPID (code=exited, status=0/SUCCESS) Main PID: 31008 (firewalld) CGroup: /system.slice/firewalld.service ?..31008 /usr/bin/python -Es /usr/sbin/firewalld --nofork --nopid Nov 25 17:53:39 CTU1000094955 systemd[1]: Starting firewalld - dynamic firewall daemon... Nov 25 17:53:40 CTU1000094955 systemd[1]: Started firewalld - dynamic firewall daemon. Nov 25 17:53:43 CTU1000094955 systemd[1]: Reloaded firewalld - dynamic firewall daemon.
注意：當我們使用systemctl的start，restart，stop和reload命令時，我們不會從終端獲取到任何輸出內容，只有status命令可以打印輸出。
14. 如何激活服務並在啟動時啟用或禁用服務（即系統啟動時自動啟動服務）
[root@CTU1000094955 ~]# systemctl is-active firewalld.service active [root@CTU1000094955 ~]# systemctl enable firewalld.service Created symlink from /etc/systemd/system/dbus-org.fedoraproject.FirewallD1.service to /usr/lib/systemd/system/firewalld.service. Created symlink from /etc/systemd/system/basic.target.wants/firewalld.service to /usr/lib/systemd/system/firewalld.service. [root@CTU1000094955 ~]# systemctl list-unit-files |grep firewall firewalld.service enabled [root@CTU1000094955 ~]# systemctl status firewalld.service ?.firewalld.service - firewalld - dynamic firewall daemon Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled; vendor preset: enabled) Active: active (running) since Sat 2017-11-25 17:53:40 CST; 4min 6s ago Main PID: 31008 (firewalld) CGroup: /system.slice/firewalld.service ?..31008 /usr/bin/python -Es /usr/sbin/firewalld --nofork --nopid Nov 25 17:53:39 CTU1000094955 systemd[1]: Starting firewalld - dynamic firewall daemon... Nov 25 17:53:40 CTU1000094955 systemd[1]: Started firewalld - dynamic firewall daemon. Nov 25 17:53:43 CTU1000094955 systemd[1]: Reloaded firewalld - dynamic firewall daemon. [root@CTU1000094955 ~]# systemctl disable firewalld.service Removed symlink /etc/systemd/system/basic.target.wants/firewalld.service. Removed symlink /etc/systemd/system/dbus-org.fedoraproject.FirewallD1.service. [root@CTU1000094955 ~]# systemctl list-unit-files |grep firewall firewalld.service disabled
15. 如何屏蔽（讓它不能啟動）或顯示服務（如 httpd.service）
[root@CTU1000094955 ~]# systemctl mask firewalld.service Created symlink from /etc/systemd/system/firewalld.service to /dev/null. [root@CTU1000094955 ~]# systemctl unmask firewalld.service Removed symlink /etc/systemd/system/firewalld.service.
16. 使用systemctl命令殺死服務
[root@CTU1000094955 ~]# systemctl kill httpd Failed to kill unit httpd.service: Unit httpd.service is not loaded. [root@CTU1000094955 ~]# systemctl kill firewalld.service [root@CTU1000094955 ~]# systemctl status firewalld.service ?.firewalld.service - firewalld - dynamic firewall daemon Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled; vendor preset: enabled) Active: inactive (dead) since Sat 2017-11-25 18:05:17 CST; 7s ago Main PID: 31008 (code=exited, status=0/SUCCESS) Nov 25 17:53:39 CTU1000094955 systemd[1]: Starting firewalld - dynamic firewall daemon... Nov 25 17:53:40 CTU1000094955 systemd[1]: Started firewalld - dynamic firewall daemon. Nov 25 17:53:43 CTU1000094955 systemd[1]: Reloaded firewalld - dynamic firewall daemon.
使用Systemctl控制並管理掛載點
17. 列出所有系統掛載點
[root@CTU1000094955 ~]# systemctl list-unit-files --type=mount UNIT FILE STATE dev-hugepages.mount static dev-mqueue.mount static proc-fs-nfsd.mount static proc-sys-fs-binfmt_misc.mount static sys-fs-fuse-connections.mount static sys-kernel-config.mount static sys-kernel-debug.mount static tmp.mount disabled var-lib-nfs-rpc_pipefs.mount static 9 unit files listed.
18. 掛載、卸載、重新掛載、重載系統掛載點並檢查系統中掛載點狀態
[root@CTU1000094955 ~]# systemctl start tmp.mount [root@CTU1000094955 ~]# systemctl stop tmp.mount [root@CTU1000094955 ~]# systemctl reload tmp.mount Job for tmp.mount invalid. [root@CTU1000094955 ~]# systemctl status tmp.mount ?.tmp.mount - Temporary Directory Loaded: loaded (/usr/lib/systemd/system/tmp.mount; disabled; vendor preset: disabled) Active: inactive (dead) since Sat 2017-11-25 18:09:06 CST; 25s ago Where: /tmp What: tmpfs Docs: man:hier(7) http://www.freedesktop.org/wiki/Software/systemd/APIFileSystems Process: 40649 ExecUnmount=/bin/umount /tmp -n (code=exited, status=0/SUCCESS) Process: 40271 ExecMount=/bin/mount tmpfs /tmp -n -t tmpfs -o mode=1777,strictatime (code=exited, status=0/SUCCESS) Nov 25 18:08:58 CTU1000094955 systemd[1]: Mounting Temporary Directory... Nov 25 18:08:58 CTU1000094955 systemd[1]: Mounted Temporary Directory. Nov 25 18:09:06 CTU1000094955 systemd[1]: Unmounting Temporary Directory... Nov 25 18:09:06 CTU1000094955 systemd[1]: Unmounted Temporary Directory. Nov 25 18:09:21 CTU1000094955 systemd[1]: Unit tmp.mount cannot be reloaded because it is inactive. [root@CTU1000094955 ~]# systemctl restart tmp.mount [root@CTU1000094955 ~]# systemctl status tmp.mount ?.tmp.mount - Temporary Directory Loaded: loaded (/usr/lib/systemd/system/tmp.mount; disabled; vendor preset: disabled) Active: active (mounted) since Sat 2017-11-25 18:09:53 CST; 2s ago Where: /tmp What: tmpfs Docs: man:hier(7) http://www.freedesktop.org/wiki/Software/systemd/APIFileSystems Process: 40649 ExecUnmount=/bin/umount /tmp -n (code=exited, status=0/SUCCESS) Process: 41410 ExecMount=/bin/mount tmpfs /tmp -n -t tmpfs -o mode=1777,strictatime (code=exited, status=0/SUCCESS) Nov 25 18:09:53 CTU1000094955 systemd[1]: tmp.mount: Directory /tmp to mount over is not empty, mounting anyway. Nov 25 18:09:53 CTU1000094955 systemd[1]: Mounting Temporary Directory... Nov 25 18:09:53 CTU1000094955 systemd[1]: Mounted Temporary Directory. [root@CTU1000094955 ~]# systemctl reload tmp.mount
19. 在啟動時激活、啟用或禁用掛載點（系統啟動時自動掛載）
[root@CTU1000094955 ~]# systemctl is-active tmp.mount active [root@CTU1000094955 ~]# systemctl disable tmp.mount Removed symlink /etc/systemd/system/local-fs.target.wants/tmp.mount. [root@CTU1000094955 ~]# systemctl is-active tmp.mount active [root@CTU1000094955 ~]# systemctl enable tmp.mount Failed to execute operation: Access denied
20. 在Linux中屏蔽（讓它不能啟用）或可見掛載點
[root@CTU1000094955 ~]# systemctl mask tmp.mount ln -s '/dev/null''/etc/systemd/system/tmp.mount' [root@CTU1000094955 ~]# systemctl unmask tmp.mount rm '/etc/systemd/system/tmp.mount'
使用Systemctl控制並管理套接口
21. 列出所有可用系統套接口
[root@CTU1000094955 ~]# systemctl list-unit-files --type=socket UNIT FILE STATE avahi-daemon.socket enabled cups.socket enabled dbus.socket static dm-event.socket enabled iscsid.socket enabled iscsiuio.socket enabled libvirtd.socket static lldpad.socket disabled lvm2-lvmetad.socket enabled lvm2-lvmpolld.socket enabled rpcbind.socket enabled rsyncd.socket disabled sshd.socket disabled syslog.socket static systemd-initctl.socket static systemd-journald.socket static systemd-networkd.socket disabled systemd-shutdownd.socket static systemd-udevd-control.socket static systemd-udevd-kernel.socket static virtlockd.socket disabled 21 unit files listed.
22. 在Linux中啟動、重啟、停止、重載套接口並檢查其狀態
[root@CTU1000094955 ~]# systemctl start sshd.socket [root@CTU1000094955 ~]# systemctl restart sshd.socket Failed to restart sshd.socket: Transaction contains conflicting jobs 'restart' and 'stop' for sshd-keygen.service. Probably contradicting requirement dependencies configured. [root@CTU1000094955 ~]# systemctl status sshd.socket ?.sshd.socket - OpenSSH Server Socket Loaded: loaded (/usr/lib/systemd/system/sshd.socket; disabled; vendor preset: disabled) Active: active (listening) since Sat 2017-11-25 18:28:12 CST; 22s ago Docs: man:sshd(8) man:sshd_config(5) Listen: [::]:22 (Stream) Accepted: 0; Connected: 0 Nov 25 18:28:12 CTU1000094955 systemd[1]: Listening on OpenSSH Server Socket. Nov 25 18:28:12 CTU1000094955 systemd[1]: Starting OpenSSH Server Socket. [root@CTU1000094955 ~]# systemctl stop sshd.socket [root@CTU1000094955 ~]# systemctl reload sshd.socket Failed to reload sshd.socket: Job type reload is not applicable for unit sshd.socket. [root@CTU1000094955 ~]# systemctl status sshd.socket ?.sshd.socket - OpenSSH Server Socket Loaded: loaded (/usr/lib/systemd/system/sshd.socket; disabled; vendor preset: disabled) Active: inactive (dead) since Sat 2017-11-25 18:28:46 CST; 19s ago Docs: man:sshd(8) man:sshd_config(5) Listen: [::]:22 (Stream) Accepted: 0; Connected: 0 Nov 25 18:28:12 CTU1000094955 systemd[1]: Listening on OpenSSH Server Socket. Nov 25 18:28:12 CTU1000094955 systemd[1]: Starting OpenSSH Server Socket. Nov 25 18:28:46 CTU1000094955 systemd[1]: Closed OpenSSH Server Socket. Nov 25 18:28:46 CTU1000094955 systemd[1]: Stopping OpenSSH Server Socket.
24. 屏蔽（使它不能啟動）或顯示套接口
[root@CTU1000094955 ~]# systemctl mask sshd.socket Created symlink from /etc/systemd/system/sshd.socket to /dev/null. [root@CTU1000094955 ~]# systemctl unmask sshd.socket Removed symlink /etc/systemd/system/sshd.socket.
服務的CPU利用率（分配額）
25. 獲取當前某個服務的CPU分配額（如httpd）
[root@CTU1000094955 ~]# systemctl show -p CPUShares httpd.service CPUShares=18446744073709551615
注意：各個服務的默認CPU分配份額=1024，你可以增加/減少某個進程的CPU分配份額。
26. 將某個服務（httpd.service）的CPU分配份額限制為2000 CPUShares/
[root@CTU1000094955 ~]# systemctl set-property httpd.service CPUShares=2000
# systemctl show -p CPUShares httpd.service
CPUShares=2000
注意：當你為某個服務設置CPUShares，會自動創建一個以服務名命名的目錄（如 httpd.service），里面包含了一個名為90-CPUShares.conf的文件，該文件含有CPUShare限制信息，你可以通過以下方式查看該文件：
[root@CTU1000094955 ~]# vi /etc/systemd/system/httpd.service.d/90-CPUShares.conf
[Service]
CPUShares=2000
27. 檢查某個服務的所有配置細節
[root@CTU1000094955 ~]# systemctl show httpd Restart=no NotifyAccess=none RestartUSec=100ms TimeoutStartUSec=1min 30s TimeoutStopUSec=1min 30s WatchdogUSec=0 WatchdogTimestampMonotonic=0 StartLimitInterval=10000000 StartLimitBurst=5 StartLimitAction=none FailureAction=none
... ... 中間省略部分內容
28. 分析某個服務（httpd）的關鍵鏈
[root@CTU1000094955 ~]# systemd-analyze critical-chain firewalld.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. firewalld.service +380ms ?..basic.target @5.903s ?..sockets.target @5.903s ?..rpcbind.socket @5.903s ?..sysinit.target @5.895s ?..systemd-update-utmp.service @5.877s +16ms ?..auditd.service @5.738s +135ms ?..systemd-tmpfiles-setup.service @5.661s +73ms ?..rhel-import-state.service @5.526s +134ms ?..local-fs.target @5.525s ?..run-user-0.mount @14.041s ?..local-fs-pre.target @1.615s ?..systemd-tmpfiles-setup-dev.service @1.519s +92ms ?..kmod-static-nodes.service @1.473s +44ms ?..systemd-journald.socket ?..-.slice
29. 獲取某個服務（httpd）的依賴性列表
[root@CTU1000094955 ~]# systemctl list-dependencies firewalld.service firewalld.service ?.?..system.slice ?.?..basic.target ?. ?..alsa-restore.service ?. ?..alsa-state.service ?.?..... ?. ?..microcode.service ?. ?..rhel-autorelabel-mark.service ?. ?..rhel-autorelabel.service ?. ?..rhel-configure.service ?. ?..rhel-dmesg.service ?. ?..rhel-loadmodules.service ?. ?..paths.target ?. ?..slices.target ... .... 后面省略部分內容
30. 按等級列出控制組
[root@CTU1000094955 ~]# systemd-cgls ?..1 /usr/lib/systemd/systemd --switched-root --system --deserialize 21 ?..user.slice ?.?..user-988.slice ?.?.?..session-c1.scope ?.?. ?..3150 gdm-session-worker [pam/gdm-launch-environment] ?.?. ?..3187 /usr/bin/gnome-session --autostart /usr/share/gdm/greeter/autostart --session gnome-initial-setup ?.?. ?..3190 /usr/bin/dbus-launch --exit-with-session /usr/bin/gnome-session --autostart /usr/share/gdm/greeter/autostart --session gnome-initial-setup ?.?. ?..3199 /bin/dbus-daemon --fork --print-pid 4 --print-address 6 --session ?.?. ?..3288 /usr/libexec/at-spi-bus-launcher ?.?. ?..3305 /bin/dbus-daemon --config-file=/etc/at-spi2/accessibility.conf --nofork --print-address 3 ?.?. ?..3309 /usr/libexec/at-spi2-registryd --use-gnome-session ?.?. ?..3410 gnome-shell --mode=initial-setup ... ... 中間省略部分內容 ?.?. ?..3767 /usr/libexec/ibus-engine-simple ?.?. ?..3879 gnome-keyring-daemon --unlock ?.?..user-0.slice
31. 按CPU、內存、輸入和輸出列出控制組
[root@CTU1000094955 ~]# systemd-cgtop Path Tasks %CPU Memory Input/s Output/s / 418 - 2.8G - - /system.slice/ModemManager.service 1 - - - - /system.slice/NetworkManager.service 1 - - - - /system.slice/abrt-oops.service 1 - - - - /system.slice/abrt-xorg.service 1 - - - - /system.slice/abrtd.service 1 - - - - /system.slice/accounts-daemon.service 1 - - - - /system.slice/alsa-state.service 1 - - - - /system.slice/atd.service 1 - - - - /system.slice/auditd.service 3 - - - -
控制系統運行等級
32. 啟動系統救援模式
[root@CTU1000094955 ~]# systemctl rescue Broadcast message from root@tecmint on pts/0(Wed2015-04-2911:31:18 IST): The system is going down to rescue mode NOW!
33. 進入緊急模式
[root@CTU1000094955 ~]# 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 intodefault mode.
34. 列出當前使用的運行等級
運行等級說明如下。
- Runlevel 0 : 關閉系統 shutdown.target
- Runlevel 1 : 緊急？維護模式 emergency.target
- Runlevel 2 : 救援？維護模式 rescure.target
- Runlevel 3 : 多用戶，無圖形系統 multi-user.target
- Runlevel 4 : 多用戶，無圖形系統 無
- Runlevel 5 : 多用戶，圖形化系統 graphical.target
- Runlevel 6 : 關閉並重啟機器 無
[root@CTU1000094955 ~]# systemctl get-default
graphical.target
35. 啟動運行等級5，即圖形模式
# systemctl isolate runlevel5.target 或 # systemctl isolate graphical.target [root@CTU1000094955 ~]# systemctl isolate runlevel5.target PolicyKit daemon disconnected from the bus. We are no longer a registered authentication agent.
36. 啟動運行等級3，即多用戶模式（命令行）
# systemctl isolate runlevel3.target
或
# systemctl isolate multiuser.target
36. 設置多用戶模式或圖形模式為默認運行等級
# systemctl set-default runlevel3.target
# systemctl set-default runlevel5.target
37. 重啟、停止、掛起、休眠系統或使系統進入混合睡眠
# systemctl reboot 重新啟動 # systemctl halt # systemctl suspend 進入睡眠模式 # systemctl hibernate 進入休眠模式 # systemctl hybrid-sleep
# systemctl rescue 強制進入救援模式
# systemctl emergency 強制進入緊急救援模式
# systemctl poweroff 系統關機