顯示所有已啟用的Unit(list-units)
因為systemctl命令的默認選項是systemctl list-units，不添加任何選項的話，將顯示list-units的結果。
另外在systemctl命令中加上--no-pager選項后將不翻頁顯示所有單元的內容。
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$ systemctl list-unitsUNIT???????????????????????????????????????????? LOAD?? ACTIVE SUB?????? DESCRIPTIONproc-sys-fs-binfmt_misc.automount??????????????? loaded active waiting?? Arbitrary Executable File Formats File System Automount Pointsys-devices-platform-serial8250-tty-ttyS1.device loaded active plugged?? /sys/devices/platform/serial8250/tty/ttyS1sys-devices-platform-serial8250-tty-ttyS2.device loaded active plugged?? /sys/devices/platform/serial8250/tty/ttyS2sys-devices-platform-serial8250-tty-ttyS3.device loaded active plugged?? /sys/devices/platform/serial8250/tty/ttyS3sys-devices-pnp0-00:09-tty-ttyS0.device????????? loaded active plugged?? /sys/devices/pnp0/00:09/tty/ttyS0(--snip--)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.96 loaded units listed. Pass --all to see loaded but inactive units, too.To show all installed unit files use 'systemctl list-unit-files'. |
統一顯示已安裝的Unit文件(list-unit-files)
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$ systemctl list-unit-filesUNIT FILE????????????????????????????? STATEproc-sys-fs-binfmt_misc.automount????? staticdev-hugepages.mount??????????????????? staticsys-kernel-debug.mount???????????????? statictmp.mount????????????????????????????? maskedvar-lib-nfs-rpc_pipefs.mount?????????? staticbrandbot.path????????????????????????? disabledarp-ethers.service???????????????????? disabledauditd.service???????????????????????? enabled(--snip--)207 unit files listed. |
比如執行了yum install httpd命令安裝Apache后，會追加這樣一個Unit文件。
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$ systemctl list-unit-files | grep httpdhttpd.service????????????????????????? disabled |
啟用Unit(enable)
啟用Unit后，會如下所示系統在開機時就會啟動服務。systemctl enable httpd命令與之前CentOS6中chkonfig httpd on的作用是一樣的。
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$ sudo systemctl enable httpdCreated symlink from /etc/systemd/system/multi-user.target.wants/httpd.service to /usr/lib/systemd/system/httpd.service.
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另外multi-user即相當于runlevel（init） 2 or 3 or 4。各運行狀態如下所示。
- runlevel0 -> poweroff 關機
- runlevel1 -> rescue 單用戶模式（救援模式）
- runlevel2 -> multi-user 多用戶模式（無網絡、字符界面）
- runlevel3 -> multi-user 多用戶模式（有網絡、字符界面）
- runlevel4 -> multi-user 備用模式（現已基本廢棄）
- runlevel5 -> graphical 圖形界面
- runlevel6 -> reboot 重啟系統
命令執行后，原本安裝后默認禁用（disable）的服務將被啟用。
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$ systemctl list-unit-files --no-pager | grep httpdhttpd.service????????????????????????? enabled |
禁用Unit(disable)
禁用后，該服務（啟動項）將被刪除。systemctl disable httpd與chkonfig httpd off作用等同。
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$ sudo systemctl disable httpdRemoved symlink /etc/systemd/system/multi-user.target.wants/httpd.service.
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使用list-unit-files命令確認是否被禁用。
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$ systemctl list-unit-files --no-pager | grep httpdhttpd.service????????????????????????? disabled |
查看Unit是否啟用/禁用(is-enable)
啟用時顯示enabled，禁用時顯示disabled。
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$ sudo systemctl is-enabled httpddisabled$ sudo systemctl enable httpdCreated symlink from /etc/systemd/system/multi-user.target.wants/httpd.service to /usr/lib/systemd/system/httpd.service.
$ sudo systemctl is-enabled httpdenabled |
Unit的再啟用(reenable)
使用再啟動命令后，會先禁用Unit后再啟用。
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$ sudo systemctl reenable httpdRemoved symlink /etc/systemd/system/multi-user.target.wants/httpd.service.
Created symlink from /etc/systemd/system/multi-user.target.wants/httpd.service to /usr/lib/systemd/system/httpd.service.
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啟動Unit(start)
service命令會顯示啟動過程，而systemctl則并不顯示啟動的詳細過程。
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$ sudo systemctl start httpd$ ps aux | grep httpdroot????? 7977? 0.3? 0.4 213704? 4880 ???????? Ss?? 01:02?? 0:00 /usr/sbin/httpd -DFOREGROUNDapache??? 7978? 0.0? 0.2 213704? 2872 ???????? S??? 01:02?? 0:00 /usr/sbin/httpd -DFOREGROUND |
Unit的狀態確認(status)
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$ sudo systemctl status httpdhttpd.service - The Apache HTTP Server???Loaded: loaded (/usr/lib/systemd/system/httpd.service; disabled)???Active: active (running) since 金 2014-10-10 01:06:07 UTC; 8s ago?Main PID: 7998 (httpd)???Status: "Processing requests..."???CGroup: /system.slice/httpd.service???????????├─7998 /usr/sbin/httpd -DFOREGROUND???????????├─7999 /usr/sbin/httpd -DFOREGROUND???????????├─8000 /usr/sbin/httpd -DFOREGROUND???????????├─8001 /usr/sbin/httpd -DFOREGROUND???????????├─8002 /usr/sbin/httpd -DFOREGROUND???????????└─8003 /usr/sbin/httpd -DFOREGROUND10月 10 01:06:07 ip-172-31-7-131 systemd[1]: Starting The Apache HTTP Server...10月 10 01:06:07 ip-172-31-7-131 systemd[1]: Started The Apache HTTP Server. |
顯示Unit的詳細信息(show)
show選項會顯示Unit的詳細信息。雖然status選項更加直觀，但在處理腳本的時候show選項使用起來更加得心應手。
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$ sudo systemctl show httpdId=httpd.serviceNames=httpd.serviceRequires=basic.targetWants=system.sliceConflicts=shutdown.targetBefore=shutdown.targetAfter=network.target remote-fs.target nss-lookup.target systemd-journald.socket basic.target system.sliceDescription=The Apache HTTP ServerLoadState=loadedActiveState=active... |
終止Unit(stop)
終止單元和其開啟過程一樣，并不顯示詳細信息。
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$ sudo systemctl stop httpd |
重新讀取Unit的配置文件(reload)
是否可重新加載取決于Unit自身。
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$ sudo systemctl reload httpd |
重啟Unit(restart)
和start、stop一樣，通常無消息提示。
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$ sudo systemctl restart httpd |
嘗試重啟Unit(try-restart)
Unit處在啟動狀態時則重啟。Unit未運行時則不進行任何操作。
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$ sudo systemctl try-restart httpd |
重新加載Unit設置或重啟(reload-or-restart)
若Unit能重新加載配置則執行reload操作，若無法重新加載配置則執行restart操作。另外Unit若處在停止狀態則啟動。
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$ sudo systemctl reload-or-restart httpd |
重新載入Unit的配置或嘗試重啟(reload-or-try-restart)
雖然與reload-or-restart同樣，但若Unit處在停止狀態時則不啟動。
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$ sudo systemctl reload-or-try-restart httpd$ sudo systemctl stop httpd$ sudo systemctl reload-or-try-restart httpdJob for httpd.service failed. See 'systemctl status httpd.service' and 'journalctl -xn' for details. |
強行終止Unit(kill)
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$ sudo systemctl kill httpd |
Unit的鎖定（遮掩）(mask/unmask)
雖然禁用(disable)Unit后也能啟動它，但使用mask命令后該服務則完全無法啟動。
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$ sudo systemctl mask httpdln -s '/dev/null' '/etc/systemd/system/httpd.service'$ sudo systemctl start httpdFailed to issue method call: Unit httpd.service is masked. |
Unit被masked后，is-enabled會提示被鎖定。
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$ sudo systemctl is-enabled httpdmasked |
解除mask需要使用unmask選項。
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$ sudo systemctl unmask httpdrm '/etc/systemd/system/httpd.service' |
確認Unit的運行狀態(is-active)
使用is-active選項，若Unit處在運行狀態則反饋active。
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$ sudo systemctl start httpd$ sudo systemctl is-active httpdactive |
若未處在運行狀態則反饋unknown。
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$ sudo systemctl stop httpd$ sudo systemctl is-active httpdunknown |
查看Unit的異常狀態(is-failed)
使用選項is-failed，若Unit正常運行則反饋active。
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$ sudo systemctl is-failed httpdactive |
若該Unit異?；蛭磫?，則反饋failed。
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$ sudo mv /etc/httpd/conf/httpd.conf /etc/httpd/conf/httpd.conf.org$ sudo systemctl restart httpdJob for httpd.service failed. See 'systemctl status httpd.service' and 'journalctl -xn' for details.$ sudo systemctl is-failed httpdfailed |
重置Unit的異常狀態(reset-failed)
systemd將重置處在異常狀態中的Unit。
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$ sudo systemctl is-failed httpdfailed$ sudo systemctl reset-failed httpd$ sudo systemctl is-failed httpdunknown |
查看Unit的依賴關系(list-dependencies)
將顯示該Unit所依賴的所有Unit。
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$ sudo systemctl list-dependencies httpdhttpd.service├─system.slice└─basic.target??├─microcode.service??├─rhel-autorelabel-mark.service??├─rhel-autorelabel.service??├─rhel-configure.service??├─rhel-dmesg.service??├─rhel-loadmodules.service??├─paths.target??├─slices.target |
寫在最后
從CentOS 6.x過來的用戶可能完全習慣了init的管理方式，對于新systemd的管理方式可能難以適應或心生厭惡。但由于systemd的強大和不斷普及，今后將很有可能成為發展主流，所以有必要深入學習并習慣這種新管理方式。
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