< Systemd 入門(mén)教程：命令篇

Systemd ???????? ??????????: ?????? ????? ???

????: ?????? ???????

?????: ???? ????? ? ?????

?? ??????, ??? Systemd ?? ???????? ?????? ??????????? ????? ???? ?? ??? ?????? ????? ?????? ??? ??????? ??? ???? ????? ??? ??????? ???? ????

??. ????????? ???? ???

?? ????? ?????????? Systemd ?????? ???, ?????? ???? ????, ???????????????? /usr/lib/systemd/system ??????????? ???? ?????????? ???? ????? ????? ??? ???? ??? ?? ?? ????????????? ????? ???? ???? ???, ????? ????? ???????? ????? (???? httpd.service ????????????)?

$ sudo systemctl enable httpd

????? ?????? ???? ?? /etc/systemd/system ???? ??????????? ???? ??????? ????? ????? ????, ?? ??????? ??? /usr/lib/systemd/system ????? httpd.service ????? ??? ???? ??? ??????? ???? ???, Systemd ????????? ??????? ???? /etc/systemd/system ?????????? ????? ?????????? ????? ?? ???? ???, ??? ??????? ?????????? ?????? ?? ??????????? ???? ???, ????? ??? ???????????? ???????? ???? ????? ?????? ?????

???, ???? ???? ????

????????? ?????? ???? ??, ???????????? ???????? ???? ??? ??, ?????? ??????? ??? ????????? ???? ?????? ???? ??????? ???? ???? ??? ???? ???? ???????????? ?????? ???, ??? ?????? ??? ?????? ???? systemctl start ????? ??? ?? ???? ???? ??, ???????????? ?????????????? ???? ??? ??, ??????? ??? ??????? ??????? ???? ???? ??? ???? ???? ???????????? ?????? ???, ??? ?????? ??? ??????? ???? ???? systemctl start ?????

x
$ sudo systemctl start httpd

????? ???????? ??????? ???? ??, ??? ???? ??? ?????? ??? ????, ??? ??????? ???? ??? systemctl status ?? ?????????? ?????? ????? ???? ???? ????

x
$ sudo systemctl status httpd
?
httpd.service - The Apache HTTP Server
 ? Loaded: loaded (/usr/lib/systemd/system/httpd.service; enabled)
 ? Active: active (running) since 金 2014-12-05 12:18:22 JST; 7min ago
 Main PID: 4349 (httpd)
 ? Status: "Total requests: 1; Current requests/sec: 0; Current traffic: ? 0 B/sec"
 ? CGroup: /system.slice/httpd.service
 ? ? ? ? ? ├─4349 /usr/sbin/httpd -DFOREGROUND
 ? ? ? ? ? ├─4350 /usr/sbin/httpd -DFOREGROUND
 ? ? ? ? ? ├─4351 /usr/sbin/httpd -DFOREGROUND
 ? ? ? ? ? ├─4352 /usr/sbin/httpd -DFOREGROUND
 ? ? ? ? ? ├─4353 /usr/sbin/httpd -DFOREGROUND
 ? ? ? ? ? └─4354 /usr/sbin/httpd -DFOREGROUND
?
12月 05 12:18:22 localhost.localdomain systemd[1]: Starting The Apache HTTP Server...
12月 05 12:18:22 localhost.localdomain systemd[1]: Started The Apache HTTP Server.
12月 05 12:22:40 localhost.localdomain systemd[1]: Started The Apache HTTP Server.

????? ???????? ????? ???? ????

??? ??? ????: ?????????? ?????? ???????, ?? ??? ?????????? ???? ??? ??? ??????? ????: ????? ???????? ??????? ??? ??? ??????????? ???? ????????? ????: ???????????? ????? (????? httpd) ?????? ??????? ???????????? ??????? ?????? ??????? ????: ?????????????? ????? ????????????? ?? ????: ?????????????? ??

???? ???? ???? ???

????? ??????? ???? ???? ????, ??????? ???? ???? systemctl stop ?????

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$ sudo systemctl stop httpd.service

有時(shí)候，該命令可能沒(méi)有響應，服務(wù)停不下來(lái)。這時(shí)候就不得不"殺進(jìn)程"了，向正在運行的進(jìn)程發(fā)出 kill ???????

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$ sudo systemctl kill httpd.service

???????, ??????? ??????? ???? ???? ???? systemctl restart ?????

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$ sudo systemctl restart httpd.service

???, ?????????? ???? ????? ???

???? ??????? ?????? ???? ???, ???????????? ?? ?????????? ???? ?????? ????????? ???? ???? ???? ???, ?????????? ????? ?? ?? ????? ???????

??? ??? ???????, ?????????? ???? ??????? ???? ??? /usr/lib/systemd/system ????, ??????? ??? ???? /etc/systemd/system ????? ?????????? ?????? ????? ??????? ??, ??? ???? ?????? ????? ????? ?????? systemctl cat ????????? ?????????? ???? ????? ???? ??????? ??? ???? ????, ???? ?????? sshd.service ??????? ?????? ???, ?? ??? ??? ???? SSH ??????? ???? ???, ???? ???????? ????????????? SSH ??????? ???? ???? ?????

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$ systemctl cat sshd.service
?
[Unit]
Description=OpenSSH server daemon
Documentation=man:sshd(8) man:sshd_config(5)
After=network.target sshd-keygen.service
Wants=sshd-keygen.service
?
[Service]
EnvironmentFile=/etc/sysconfig/sshd
ExecStart=/usr/sbin/sshd -D $OPTIONS
ExecReload=/bin/kill -HUP $MAINPID
Type=simple
KillMode=process
Restart=on-failure
RestartSec=42s
?
[Install]
WantedBy=multi-user.target

???? ??????, ?????????? ?????? ??????? ????? ??????, ??????? ????? ??????? ??-??? ???? ???????

???? ??????? ?????? ?????????? ???????? ??? ???????

????, [?????] ????: ???? ???? ???? ??? ?????????????

Unit ?????? Description ??????? ??????? ????? ???? ??? ?????? ?????? ???, Documentation ??????? ?????????? ??????? ??????? ??????? ??????? ???? ???? ???? ??? ???????????, ??? ??? ?????????????

After ???????: ??????? ??? ??? network.target ???? sshd-keygen.service ??????????? ???? ????, ????? sshd.service ????? ??? ???? ??? ?????

????????, ??? ???? ???? Before ???????, ?????? sshd.service ??? ????? ??? ???? ??? ????? ?????? ????, After ??? Before ????????? ???? ???? ???? ?????? ???? ?????????, ????????? ???? ????

????????????, ???? ????? ?????????????? ??????????????? ???????? ???? ????????? ????????? ?????????? ?????, ??? ???? ??????????????? ???? ???? ???? ?????????? ??? ??????, ?????? ??????????????? ??? ???????? ?????????? ??? ?????? ???? ?????? ???, ??? ????? ??????????????? ??????? ???? ???? ???, ??????? ???? ????? ????, ??? ????? ???????????? ??????? ????? ?????? ???? ????? ???? ???????? ??? ????, ??????? ???? ??? Wants ??????? ??? Requires ????????

Wants ???????: ?????? ??? sshd.service ???? sshd-keygen.service 之間存在"弱依賴(lài)"關(guān)系，即如果"sshd-keygen.service"啟動(dòng)失敗或停止運行，不影響 sshd.service ??????? ??????

Requires 字段則表示"強依賴(lài)"關(guān)系，即如果該服務(wù)啟動(dòng)失敗或異常退出，那么 sshd.service ??? ?????? ??????? ???? ????

?????? ???, Wants ????? ??? Requires ??????? ????????? ???????? ?????????, ???? ???? ?????? ???? ???? ??????? ???, ?????????? ??? ??? ????? ???? ????

???, [???????] ?????: ???? ????

Service ???? ???????? ?????? ??????? ??????? ???? ????

?.? ???? ???? ????

???? ???????????? ?????? ?????? ??????????? ???? ??????, ?? ??????? ??? ???? ????? EnvironmentFile ??????? ?????

EnvironmentFile ?????: ??????? ???????? ?????? ??????????? ???? ???????? ????? ?? ?????? ????? key=value ??-??? ????, ??????? ??? ???? $key ??????? ?????????? ????? ????? ??????? ????

????? ???????, sshd ?? ?????? ??????????? ???? ?? /etc/sysconfig/sshd ?????????? ?????? ??????? ???????????? ??????? ?? ExecStart 。

ExecStart ?????: ?????????? ???? ???? ???? ??????? ??? ?????? ?????????? ????

????? ???????, ???? ??? sshd ??????? ???? ???? ?? /usr/sbin/sshd -D $OPTIONS ?????? ????????????? $OPTIONS ??? ???? ????? EnvironmentFile ????? ?????? ????????? ?????? ??????????? ????? ?? ???? ???? ???????? ???????? ????????? ????

ExecReload ?????: ??????? ???? ???? ???? ??????? ??? ??????

ExecStop ?????: ??????? ???? ???? ???? ??????? ??? ??????

ExecStartPre ?????: ??????? ???? ???? ??? ??????? ???? ??????

ExecStartPost ?????: ??????? ???? ???? ??? ??????? ??? ??????

ExecStopPost ?????: ???? ???? ???? ?? ??????? ??? ??? ??? ??????

???? ??? ????? ???????? ??????

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[Service]
ExecStart=/bin/echo execstart1
ExecStart=
ExecStart=/bin/echo execstart2
ExecStartPost=/bin/echo post1
ExecStartPost=/bin/echo post2

?? ?????????? ?????? ???????? ???? ExecStart ????? ??? ??? ??? ??????, ????? ?????? ????? ????? ??? ??????, ????? ???? ?????? ???

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execstart2
post1
post2

??? ????????? ???????? ??? ???? ????????? ????? ??? ??? ???? ???? ( - ），表示"抑制錯誤"，即發(fā)生錯誤的時(shí)候，不影響其他命令的執行。比如， EnvironmentFile=-/etc/sysconfig/sshd (????????? ???? ??????? ??? ?? ?????? ??????? ???), ??? ??????? ??? ?? ???? /etc/sysconfig/sshd ?????? ???, ??? ??? ?????? ???????

?.? ???? ???? ???

Type ????? ???????? ????????? ????? ??? ??? ??? ???? ???? ??? ??????? ?????????

?????? (?????? ???): ExecStart ????? ???? ??? ?????????? ?????? ???????????

forking： ExecStart ??????? ??? fork() ?????? ???? ???, ?? ???? ???? ?????????? ??? ???? ????, ??? ???? ?????????? ?????? ?????????? ???? ?????

????: ?????? simple ?????? ??? ????????? ????? ??????? ???, Systemd ??? ??????? ????? ??????? ??????? ????, ????? ???????? ??????????? ???? ?????

?????: ?? ??? simple ?????? D-Bus ??????? ???? ??????? ??? ???? ????

???????: ?????? simple ???? ???? ??? ???? ????????? ???????? ?????? ???, ????? Systemd ???????? ??????????? ???? ???? ?????

??????: ?????? simple ?????? ???? ??????? ??????? ????? ??????? ?? ????????? ???? ??? ??? ???? ????????? ????????? ??? ?? ???????? ?????? ???? ???????? ???????? ???? ??????? ?? ?????? ?????

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[Unit]
Description=Switch-off Touchpad
?
[Service]
Type=oneshot
ExecStart=/usr/bin/touchpad-off
?
[Install]
WantedBy=multi-user.target

????? ?????????? ?????? ???? ???? ??? ???????? ???? oneshot ??? ??????? ??? ?? ?? ????????? ????? ??????? ??????, ???????????????? ??????? ???????? ???? ??? ??? ???? ??? ??? ??? ??? ???? ???? ???? ???, ?????????? ?????? ????? ??? ???????? ?????

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[Unit]
Description=Switch-off Touchpad
?
[Service]
Type=oneshot
ExecStart=/usr/bin/touchpad-off start
ExecStop=/usr/bin/touchpad-off stop
RemainAfterExit=yes
?
[Install]
WantedBy=multi-user.target

????? ?????????? ?????, RemainAfterExit ????? ??? ???? yes ?????????? ??? ?????? ???, ????????? ???? ??????? ?????? ??????, ????? ??????? ???? ??? systemctl stop ???? ???? ???? ????? ExecStop ????????? ???????? ??????? ???, ??? ???????? ??????? ???? ????

?.? ??????? ???? ???? ????

Service ??????? ???? ??????? ??????, ?? ??????? ???? ???? ???? ?????????? ????

KillMode ?????: ???????? ?????? sshd ??????? ???? ??? ?? ?????????? ????

????? ?? ???????,將 KillMode ???????? ???? process ??? ??? ?????????? ???? ???? ???? ?????? ???, ?????? ???? sshd ???????????? ???? ??? ??, ?????? ?????????????? ???? SSH ???? ???? ????? ????? ????? ?? ??????? ??? ?????? ???, ??? sshd ?? ???? ????????????, ???????? ???? ??? ??????? ???? ????, ??? ???? ????? ???? SSH ??????? ????? ??????

KillMode ?????? ??? ??? ???? ???? ??? ??? ???? ?????? ???

??????????-????? (?????? ???): ??????? ?????????? ??????? ????? ????? ??-?????????? ????? ??? ????

??????????: ????????? ?????? ?????????? ????? ????

???????: ?????? ?????????? SIGTERM ????? ????? ????, ??? ??-?????????? SIGKILL ????? ????? ?????

???? ?????????? ????? ??? ??? ??, ????????? ???????? ???? ?????? ?????? ????

??????? ?? Restart ????????

Restart ?????: sshd ??? ?????? ?? Systemd ?? ??????? ???? ???? ?????? ?????????? ????

????? ???????, Restart ???????? ???? on-failure ?????? ??????????? ????????? ????, sshd ??????? ???? ??? ???? ??? sshd ???????? ???? ??? (???? ??????? ???) systemctl stop ??? ??????? ???? ??? ???

Restart ?????? ??? ??? ???? ???? ??? ??? ???? ?????? ???

?? (?????? ???): ???????? ???? ??? ??????? ???? ??? ???

on-success: ????????? ????????????? ???????? ???? ???? (???????? ?????? ??? 0 ???) ??? ??????? ???? ????

on-failure: ?????????? ???????? ??? (???????? ????????? ??? 0 ?? ?????), ???????? ?????? ???? ??? ??? ??????? ??, ???? ??????? ???? ????

????????????: ????????? ????? ???? ??? ??????? ??? ??????? ???? ????

on-abort: ????????? ??? ???? ?????? ?????????? ????? ??????? ???, ???? ??????? ???? ????

??-???????: ???????? ??? ???, ???? ??????? ???? ????

?????? ???????? ????? ???, ?????? ??????? ???? ?????

?????? ????, ??? ??? ??????? ??? ??? on-failure ???? ?????? ??? ???????? ???? ????, ?????? ??? ??? ???? ????? on-abnormal 。

??? ??? RestartSec ????????

RestartSec ?????: ???????? ??????? ??????? ???? ???? ??? ??????? ???? ??? ??? ????????? ??????? ????? ??????? 42 ??????? ??????? ???? ??? ??? ???????

???, [??????] ????

Install ????, ?? ?????????? ?????? ?????? ?????? ???? ??? ?? ?????????? ????, ?????? ?????? ??? ??? ?? ???? ???? ???? ??? ?????

WantedBy ???????: ?? ????????? ?????? ??????? ?? ??????? ????

Target ?? ???? ?? ??????? ?????, ?? ???? ???????? ???? ????? ??????? ???? WantedBy=multi-user.target ??? ??????, sshd ?????? ??????? ?????? ?? multi-user.target ?? ??????? ??????? ????????????, ???? ??? ??????? ???? systemctl enable sshd.service ??????? ??????? ????, sshd.service ???? ??????? ?????, ??? ?????? ??? ??? /etc/systemd/system ?????????? ???? multi-user.target.wants ????????????? ?????? Systemd-?? ?????? ??????? ??????? ???????

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$ systemctl get-default
multi-user.target

????? ??????? ??????? ??? ??, ?????? ???? ???? ?????? ?? multi-user.target ?? ??????? ??? ??????? ???????????????? ???? ???? ???? ????? systemctl enable ???? ?????? ??? ???? ???? ???? ??? ??? ????? ??????? ??????? ???? ????, systemctl list-dependencies ???? ??? systemctl isolate ????? ???? ???????

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# multi-user.target ?? ???? ????????? ????? ???? ?????
$ systemctl list-dependencies multi-user.target
?
# ???? ???????? ?????? ????
# shutdown.target ?? ???? ???? ???????
$ sudo systemctl isolate shutdown.target

??????????, ??????? ??????? ??????? ???? ???: ???? ?? multi-user.target , ?????? ??????????? ?????? ???? ??????? ???????????? ???; ?????? ?? graphical.target ??? ??????????? ????? ????? ??????, ??? ?????? ??? multi-user.target ???????? ????? ???? ??? ?????? ??? ??????? ??????? ???????? ????? 。

?. Target ?? ?????????? ????

?????????? ?????? ?????????? ???? ???????

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$ systemctl cat multi-user.target
?
[Unit]
Description=Multi-User System
Documentation=man:systemd.special(7)
Requires=basic.target
Conflicts=rescue.service rescue.target
After=basic.target rescue.service rescue.target
AllowIsolate=yes

???? ??? ?????? ????, ??????? ?????????? ????? ??? ??????? ?????? ???? ????? ?????? ?????? ?????? ???????????? ???? ?????????

Requires ?????: ???? basic.target ?????? ?????

Conflicts ???????: ????? ???????? ??? rescue.service ???? rescue.target ????, multi-user.target ??? ?????? ???? ??, ?????? ?????

After ???????????? ??? multi-user.target ????? basic.target 、 rescue.service 、 rescue.target ???? ???? ????, ??? ?????? ???? ????

AllowIsolate ?????? ?????? ?????? systemctl isolate ?????? ???????? ???? multi-user.target 。

???? ?????????? ???? ???????? ???? ?? ??????? ???? ?????

?????????? ???? ?????? ???? ??, ?????????? ???? ??????? ??? ???? ???, ????? ????????? ??????????? ??????? ???? ???? ????

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# ?????????? ???? ??????? ??? ????
$ sudo systemctl daemon-reload
?
# ????????? ??????????? ??????? ???? ????
$ sudo systemctl restart foobar

(??????)

?????????? ????

??????? ?????: ????? ??????????-??????????-??????? ???-???????? ????? ????? ( ?????????? ????? ?.? ???????? ）

???????? ?????: ???? ????? ?? ?????