[root@hadoop01 hadoop]# systemctl --help systemctl [OPTIONS...] {COMMAND} ... Query or send control commands to the systemd manager. -h --help Show this help --version Show package version --system Connect to system manager -H --host=[USER@]HOST Operate on remote host -M --machine=CONTAINER Operate on local container -t --type=TYPE List units of a particular type --state=STATE List units with particular LOAD or SUB or ACTIVE state -p --property=NAME Show only properties by this name -a --all Show all loaded units/properties, including dead/empty ones. To list all units installed on the system, use the 'list-unit-files' command instead. -l --full Don't ellipsize unit names on output -r --recursive Show unit list of host and local containers --reverse Show reverse dependencies with 'list-dependencies' --job-mode=MODE Specify how to deal with already queued jobs, when queueing a new job --show-types When showing sockets, explicitly show their type -i --ignore-inhibitors When shutting down or sleeping, ignore inhibitors --kill-who=WHO Who to send signal to -s --signal=SIGNAL Which signal to send --now Start or stop unit in addition to enabling or disabling it -q --quiet Suppress output --no-block Do not wait until operation finished --no-wall Don't send wall message before halt/power-off/reboot --no-reload Don't reload daemon after en-/dis-abling unit files --no-legend Do not print a legend (column headers and hints) --no-pager Do not pipe output into a pager --no-ask-password Do not ask for system passwords --global Enable/disable unit files globally --runtime Enable unit files only temporarily until next reboot -f --force When enabling unit files, override existing symlinks When shutting down, execute action immediately --preset-mode= Apply only enable, only disable, or all presets --root=PATH Enable unit files in the specified root directory -n --lines=INTEGER Number of journal entries to show -o --output=STRING Change journal output mode (short, short-iso, short-precise, short-monotonic, verbose, export, json, json-pretty, json-sse, cat) --plain Print unit dependencies as a list instead of a tree Unit Commands: list-units [PATTERN...] List loaded units list-sockets [PATTERN...] List loaded sockets ordered by address list-timers [PATTERN...] List loaded timers ordered by next elapse start NAME... Start (activate) one or more units stop NAME... Stop (deactivate) one or more units reload NAME... Reload one or more units restart NAME... Start or restart one or more units try-restart NAME... Restart one or more units if active reload-or-restart NAME... Reload one or more units if possible, otherwise start or restart reload-or-try-restart NAME... Reload one or more units if possible, otherwise restart if active isolate NAME Start one unit and stop all others kill NAME... Send signal to processes of a unit is-active PATTERN... Check whether units are active is-failed PATTERN... Check whether units are failed status [PATTERN...|PID...] Show runtime status of one or more units show [PATTERN...|JOB...] Show properties of one or more units/jobs or the manager cat PATTERN... Show files and drop-ins of one or more units set-property NAME ASSIGNMENT... Sets one or more properties of a unit help PATTERN...|PID... Show manual for one or more units reset-failed [PATTERN...] Reset failed state for all, one, or more units list-dependencies [NAME] Recursively show units which are required or wanted by this unit or by which this unit is required or wanted systemctl [OPTIONS...] {COMMAND} ... Query or send control commands to the systemd manager. -h --help Show this help --version Show package version systemctl [OPTIONS...] {COMMAND} ... systemctl [OPTIONS...] {COMMAND} ... Query or send control commands to the systemd manager. -h --help Show this help --version Show package version --system Connect to system manager -H --host=[USER@]HOST Operate on remote host -M --machine=CONTAINER Operate on local container -t --type=TYPE List units of a particular type --state=STATE List units with particular LOAD or SUB or ACTIVE state -p --property=NAME Show only properties by this name -a --all Show all loaded units/properties, including dead/empty ones. To list all units installed on the system, use the 'list-unit-files' command instead. -l --full Don't ellipsize unit names on output -r --recursive Show unit list of host and local containers --reverse Show reverse dependencies with 'list-dependencies' --job-mode=MODE Specify how to deal with already queued jobs, when queueing a new job --show-types When showing sockets, explicitly show their type -i --ignore-inhibitors When shutting down or sleeping, ignore inhibitors --kill-who=WHO Who to send signal to -s --signal=SIGNAL Which signal to send --now Start or stop unit in addition to enabling or disabling it -q --quiet Suppress output --no-block Do not wait until operation finished --no-wall Don't send wall message before halt/power-off/reboot --no-reload Don't reload daemon after en-/dis-abling unit files --no-legend Do not print a legend (column headers and hints) --no-pager Do not pipe output into a pager --no-ask-password Do not ask for system passwords --global Enable/disable unit files globally --runtime Enable unit files only temporarily until next reboot -f --force When enabling unit files, override existing symlinks When shutting down, execute action immediately --preset-mode= Apply only enable, only disable, or all presets --root=PATH Enable unit files in the specified root directory -n --lines=INTEGER Number of journal entries to show -o --output=STRING Change journal output mode (short, short-iso, short-precise, short-monotonic, verbose, export, json, json-pretty, json-sse, cat) --plain Print unit dependencies as a list instead of a tree Unit Commands: list-units [PATTERN...] List loaded units list-sockets [PATTERN...] List loaded sockets ordered by address list-timers [PATTERN...] List loaded timers ordered by next elapse start NAME... Start (activate) one or more units stop NAME... Stop (deactivate) one or more units reload NAME... Reload one or more units restart NAME... Start or restart one or more units try-restart NAME... Restart one or more units if active reload-or-restart NAME... Reload one or more units if possible, otherwise start or restart reload-or-try-restart NAME... Reload one or more units if possible, otherwise restart if active isolate NAME Start one unit and stop all others kill NAME... Send signal to processes of a unit is-active PATTERN... Check whether units are active is-failed PATTERN... Check whether units are failed status [PATTERN...|PID...] Show runtime status of one or more units show [PATTERN...|JOB...] Show properties of one or more units/jobs or the manager cat PATTERN... Show files and drop-ins of one or more units set-property NAME ASSIGNMENT... Sets one or more properties of a unit help PATTERN...|PID... Show manual for one or more units reset-failed [PATTERN...] Reset failed state for all, one, or more units list-dependencies [NAME] Recursively show units which are required or wanted by this unit or by which this unit is required or wanted Unit File Commands: list-unit-files [PATTERN...] List installed unit files enable NAME... Enable one or more unit files disable NAME... Disable one or more unit files reenable NAME... Reenable one or more unit files preset NAME... Enable/disable one or more unit files based on preset configuration preset-all Enable/disable all unit files based on preset configuration is-enabled NAME... Check whether unit files are enabled mask NAME... Mask one or more units unmask NAME... Unmask one or more units link PATH... Link one or more units files into the search path add-wants TARGET NAME... Add 'Wants' dependency for the target on specified one or more units add-requires TARGET NAME... Add 'Requires' dependency for the target on specified one or more units edit NAME... Edit one or more unit files get-default Get the name of the default target set-default NAME Set the default target Machine Commands: list-machines [PATTERN...] List local containers and host Job Commands: list-jobs [PATTERN...] List jobs cancel [JOB...] Cancel all, one, or more jobs Snapshot Commands: snapshot [NAME] Create a snapshot delete NAME... Remove one or more snapshots Environment Commands: show-environment Dump environment set-environment NAME=VALUE... Set one or more environment variables unset-environment NAME... Unset one or more environment variables import-environment [NAME...] Import all or some environment variables Manager Lifecycle Commands: daemon-reload Reload systemd manager configuration daemon-reexec Reexecute systemd manager System Commands: is-system-running Check whether system is fully running default Enter system default mode rescue Enter system rescue mode emergency Enter system emergency mode halt Shut down and halt the system poweroff Shut down and power-off the system reboot [ARG] Shut down and reboot the system kexec Shut down and reboot the system with kexec exit Request user instance exit switch-root ROOT [INIT] Change to a different root file system suspend Suspend the system hibernate Hibernate the system hybrid-sleep Hibernate and suspend the system
一、Systemd簡介
Systemd是由紅帽公司的一名叫做Lennart Poettering的員工開發，systemd是Linux系統中最新的初始化系統（init）,它主要的設計目的是克服Sys V 固有的缺點，提高系統的啟動速度。
systemd和upstart是競爭對手，ubantu上使用的是upstart的啟動方式，centos7上使用systemd替換了Sys V，Systemd目錄是要取代Unix時代依賴一直在使用的init系統，兼容SysV和LSB的啟動腳本，
而且能夠在進程啟動中更有效地引導加載服務。
system：系統啟動和服務器守護進程管理器，負責在系統啟動或運行時，激活系統資源，服務器進程和其他進程，根據管理，字母d是守護進程（daemon）的縮寫，systemd這個名字的含義就是它要守護整個系統。
二、Systemd新特性
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系統引導時實現服務並行啟動
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按需啟動守護進程
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自動化的服務依賴關系管理
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同時采用socket式與D-Bus總線式激活服務
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系統狀態快照和恢復
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利用Linux的cgroups監視進程
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維護掛載點和自動掛載點
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各服務間基於依賴關系進行精密控制
三、Systemd核心概念
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Unit
表示不同類型的sytemd對象，通過配置文件進行標識和配置，文件中主要包含了系統服務，監聽socket、保存的系統快照以及其他與init相關的信息 -
配置文件:
/usr/lib/systemd/system：每個服務最主要的啟動腳本設置，類似於之前的/etc/initd.d
/run/system/system：系統執行過程中所產生的服務腳本，比上面的目錄優先運行
/etc/system/system：管理員建立的執行腳本，類似於/etc/rc.d/rcN.d/Sxx類的功能，比上面目錄優先運行，在三者之中，此目錄優先級最高
四、Unit類型
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systemctl -t help ：查看unit類型
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service unit：文件擴展名為.service，用於定義系統服務
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target unit：文件擴展名為.target，用於模擬實現“運行級別”
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device unit: .device,用於定義內核識別的設備
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mount unit ：.mount，定義文件系統掛載點
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socket unit ：.socket,用於標識進程間通信用的socket文件，也可以在系統啟動時，延遲啟動服務，實現按需啟動
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snapshot unit：.snapshot，關系系統快照
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swap unit：.swap，用於表示swap設備
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automount unit：.automount，文件系統的自動掛載點如：/misc目錄
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path unit：.path，用於定義文件系統中的一個文件或目錄使用，常用於當文件系統變化時，延遲激活服務，如spool目錄
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time：.timer由systemd管理的計時器
注：使用systemctl控制單元時，通常需要使用單元文件的全名，包括擴展名，但是有些單元可以在systemctl中使用簡寫方式，如果無擴展名，systemctl默認把擴展名當做.service。例如netcfg和netcfg.service是等同的掛載點會自動轉化為相應的.mount單元，例如/home等價於home.mount設備會自動轉化為相應的.device單元，所以/dev/sd2等價於dev-sda2.device
五、關鍵特性
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基於socket的激活機制：socket與服務進程分離
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基於D-Bus的激活機制
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基於device的激活機制
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基於path的激活機制
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系統快照：保存各unit的當前狀態信息於持久存儲設備中想后兼容sysv init腳本
六、不兼容
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systemctl命令固定不變，不可擴展
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非由systemd啟動的服務，systemctl無語與之通信和控制，如：使用之前sys v風格管理的進程就無法收systemd控制
七、Systemd基本工具
監視和控制systemd的主要命令是systemctl。該命令可用於查看系統狀態和管理系統及服務。
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管理服務
命令：systemctl command name.service
啟動：service name start –>systemctl start name.service
停止：service name stop –>systemctl stop name.service
重啟：service name restart–>systemctl restart name.service
狀態：service name status–>systemctl status name.service
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條件式重啟(已啟動才重啟，否則不做任何操作)
systemctl try-restart name.service -
重載或重啟服務(先加載，然后再啟動)
systemctl reload-or-try-restart name.service -
禁止自動和手動啟動
systemctl mask name.service
執行此條命令實則創建了一個鏈接 ln -s '/dev/null' '/etc/systemd/system/sshd.service' -
取消禁止
systemctl unmask name.service
刪除此前創建的鏈接 -
服務查看(查看某服務當前激活與否的狀態)
systemctl is-active name.service
如果啟動會顯示active，否則會顯示unknown -
查看所有已經激活的服務
systemctl list-units –t|–type service
[root@hadoop01 hadoop]# systemctl --helpsystemctl [OPTIONS...] {COMMAND} ...
Query or send control commands to the systemd manager.
-h --help Show this help --version Show package version --system Connect to system manager -H --host=[USER@]HOST Operate on remote host -M --machine=CONTAINER Operate on local container -t --type=TYPE List units of a particular type --state=STATE List units with particular LOAD or SUB or ACTIVE state -p --property=NAME Show only properties by this name -a --all Show all loaded units/properties, including dead/empty ones. To list all units installed on the system, use the 'list-unit-files' command instead. -l --full Don't ellipsize unit names on output -r --recursive Show unit list of host and local containers --reverse Show reverse dependencies with 'list-dependencies' --job-mode=MODE Specify how to deal with already queued jobs, when queueing a new job --show-types When showing sockets, explicitly show their type -i --ignore-inhibitors When shutting down or sleeping, ignore inhibitors --kill-who=WHO Who to send signal to -s --signal=SIGNAL Which signal to send --now Start or stop unit in addition to enabling or disabling it -q --quiet Suppress output --no-block Do not wait until operation finished --no-wall Don't send wall message before halt/power-off/reboot --no-reload Don't reload daemon after en-/dis-abling unit files --no-legend Do not print a legend (column headers and hints) --no-pager Do not pipe output into a pager --no-ask-password Do not ask for system passwords --global Enable/disable unit files globally --runtime Enable unit files only temporarily until next reboot -f --force When enabling unit files, override existing symlinks When shutting down, execute action immediately --preset-mode= Apply only enable, only disable, or all presets --root=PATH Enable unit files in the specified root directory -n --lines=INTEGER Number of journal entries to show -o --output=STRING Change journal output mode (short, short-iso, short-precise, short-monotonic, verbose, export, json, json-pretty, json-sse, cat) --plain Print unit dependencies as a list instead of a tree
Unit Commands: list-units [PATTERN...] List loaded units list-sockets [PATTERN...] List loaded sockets ordered by address list-timers [PATTERN...] List loaded timers ordered by next elapse start NAME... Start (activate) one or more units stop NAME... Stop (deactivate) one or more units reload NAME... Reload one or more units restart NAME... Start or restart one or more units try-restart NAME... Restart one or more units if active reload-or-restart NAME... Reload one or more units if possible, otherwise start or restart reload-or-try-restart NAME... Reload one or more units if possible, otherwise restart if active isolate NAME Start one unit and stop all others kill NAME... Send signal to processes of a unit is-active PATTERN... Check whether units are active is-failed PATTERN... Check whether units are failed status [PATTERN...|PID...] Show runtime status of one or more units show [PATTERN...|JOB...] Show properties of one or more units/jobs or the manager cat PATTERN... Show files and drop-ins of one or more units set-property NAME ASSIGNMENT... Sets one or more properties of a unit help PATTERN...|PID... Show manual for one or more units reset-failed [PATTERN...] Reset failed state for all, one, or more units list-dependencies [NAME] Recursively show units which are required or wanted by this unit or by which this unit is required or wanted
systemctl [OPTIONS...] {COMMAND} ...
Query or send control commands to the systemd manager.
-h --help Show this help --version Show package versionsystemctl [OPTIONS...] {COMMAND} ...
systemctl [OPTIONS...] {COMMAND} ...
Query or send control commands to the systemd manager.
-h --help Show this help --version Show package version --system Connect to system manager -H --host=[USER@]HOST Operate on remote host -M --machine=CONTAINER Operate on local container -t --type=TYPE List units of a particular type --state=STATE List units with particular LOAD or SUB or ACTIVE state -p --property=NAME Show only properties by this name -a --all Show all loaded units/properties, including dead/empty ones. To list all units installed on the system, use the 'list-unit-files' command instead. -l --full Don't ellipsize unit names on output -r --recursive Show unit list of host and local containers --reverse Show reverse dependencies with 'list-dependencies' --job-mode=MODE Specify how to deal with already queued jobs, when queueing a new job --show-types When showing sockets, explicitly show their type -i --ignore-inhibitors When shutting down or sleeping, ignore inhibitors --kill-who=WHO Who to send signal to -s --signal=SIGNAL Which signal to send --now Start or stop unit in addition to enabling or disabling it -q --quiet Suppress output --no-block Do not wait until operation finished --no-wall Don't send wall message before halt/power-off/reboot --no-reload Don't reload daemon after en-/dis-abling unit files --no-legend Do not print a legend (column headers and hints) --no-pager Do not pipe output into a pager --no-ask-password Do not ask for system passwords --global Enable/disable unit files globally --runtime Enable unit files only temporarily until next reboot -f --force When enabling unit files, override existing symlinks When shutting down, execute action immediately --preset-mode= Apply only enable, only disable, or all presets --root=PATH Enable unit files in the specified root directory -n --lines=INTEGER Number of journal entries to show -o --output=STRING Change journal output mode (short, short-iso, short-precise, short-monotonic, verbose, export, json, json-pretty, json-sse, cat) --plain Print unit dependencies as a list instead of a tree
Unit Commands: list-units [PATTERN...] List loaded units list-sockets [PATTERN...] List loaded sockets ordered by address list-timers [PATTERN...] List loaded timers ordered by next elapse start NAME... Start (activate) one or more units stop NAME... Stop (deactivate) one or more units reload NAME... Reload one or more units restart NAME... Start or restart one or more units try-restart NAME... Restart one or more units if active reload-or-restart NAME... Reload one or more units if possible, otherwise start or restart reload-or-try-restart NAME... Reload one or more units if possible, otherwise restart if active isolate NAME Start one unit and stop all others kill NAME... Send signal to processes of a unit is-active PATTERN... Check whether units are active is-failed PATTERN... Check whether units are failed status [PATTERN...|PID...] Show runtime status of one or more units show [PATTERN...|JOB...] Show properties of one or more units/jobs or the manager cat PATTERN... Show files and drop-ins of one or more units set-property NAME ASSIGNMENT... Sets one or more properties of a unit help PATTERN...|PID... Show manual for one or more units reset-failed [PATTERN...] Reset failed state for all, one, or more units list-dependencies [NAME] Recursively show units which are required or wanted by this unit or by which this unit is required or wanted
Unit File Commands: list-unit-files [PATTERN...] List installed unit files enable NAME... Enable one or more unit files disable NAME... Disable one or more unit files reenable NAME... Reenable one or more unit files preset NAME... Enable/disable one or more unit files based on preset configuration preset-all Enable/disable all unit files based on preset configuration is-enabled NAME... Check whether unit files are enabled mask NAME... Mask one or more units unmask NAME... Unmask one or more units link PATH... Link one or more units files into the search path add-wants TARGET NAME... Add 'Wants' dependency for the target on specified one or more units add-requires TARGET NAME... Add 'Requires' dependency for the target on specified one or more units edit NAME... Edit one or more unit files get-default Get the name of the default target set-default NAME Set the default target
Machine Commands: list-machines [PATTERN...] List local containers and host
Job Commands: list-jobs [PATTERN...] List jobs cancel [JOB...] Cancel all, one, or more jobs
Snapshot Commands: snapshot [NAME] Create a snapshot delete NAME... Remove one or more snapshots
Environment Commands: show-environment Dump environment set-environment NAME=VALUE... Set one or more environment variables unset-environment NAME... Unset one or more environment variables import-environment [NAME...] Import all or some environment variables
Manager Lifecycle Commands: daemon-reload Reload systemd manager configuration daemon-reexec Reexecute systemd manager
System Commands: is-system-running Check whether system is fully running default Enter system default mode rescue Enter system rescue mode emergency Enter system emergency mode halt Shut down and halt the system poweroff Shut down and power-off the system reboot [ARG] Shut down and reboot the system kexec Shut down and reboot the system with kexec exit Request user instance exit switch-root ROOT [INIT] Change to a different root file system suspend Suspend the system hibernate Hibernate the system hybrid-sleep Hibernate and suspend the system