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

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

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

Systemd ?????????? ??????????: ?????? ??? ??. ??? ???, Systemd ?? ?????????? ???? ??????? ??????????? 3.1 systemctl 3.2 systemd-analyze 3.3 hostnamectl 3.4 localectl 3.5 timedatectl 3.6 loginctl ???, ????? ?.? ???? ?.? ??????? ?????? ?.? ????? ???????? ?.? ???????????? ????, ??????? ?????????? ???? ?.? ?????????? ?.? ?????????? ?????? ?????? ?.? ?????????? ?????? ??????? 5.4 ?????????? ?????? ???? ???, ?????? ???. ?? ??????????? ?????????? ????

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

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

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

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

??. ???

???????, ????????? ???? ???? ????? ??? ?????? init ???????????

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


xxxxxxxxxx
			
			
			
			
				
					
					
					$ sudo /etc/init.d/apache2 start
				
				# ????
				
					$ service apache2 start

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

???? ?? ???? ???? ???? ?????? init ?????????????? ????????????? ???? ???, ????????? ?????????? ?????????? ??????? ??? ??????? ?????????? ???? ????

?????????, ????????? ???? ??? ????? init ?????????? ????????? ???????? ????????? ??????, ???? ???? ????? ?????? ??? ??? ????????????? ??????? ????????? ???????? ???? ???, ?? ???????? ????????????? ??? ????? ??? ?????

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

Systemd ?? ?????????? ???????? ???? ???? ??????? ?? ?????? ?????? ?? ????????? ???? ??? ???????????? ???? ???? ???????? ?????? ?????? ????

????????? ?????? ???????, ????? d ??? ???? (daemon) ?? ????????? ???? Systemd ?? ?????? ???? ??? ??? ???? ????????? ????? ?????

(????? ????? Systemd ??????) Lennart Poettering ）

Systemd ??????? ???? ?? ????? ??? init ???????? ??????????? ????? initd ????????? ????? ?????????? ???? ??? (PID ???? 1), ???? ?????????????? ?? ??????? ???????????


xxxxxxxxxx
				
				
				
				
					
						
						
						$ systemctl --version

????? ???????? Systemd ?? ??????? ???????

Systemd 的優(yōu)點(diǎn)是功能強大，使用方便，缺點(diǎn)是體系龐大，非常復雜。事實(shí)上，現在還有很多人反對使用 Systemd，理由就是它過(guò)于復雜，與操作系統的其他部分強耦合，違反"keep simple, keep stupid"的 ??????? ?????

(????? ??????? Systemd ???????? ?????)

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

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

3.1 systemctl

systemctl ??? Systemd ?? ?????? ??????, ?? ??????? ????????? ???? ??????? ????


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						# ??????? ??????? ???? ????
					
					$ sudo systemctl reboot
					?
					# ??????? ???? ????, ??????? ???? ???
					$ sudo systemctl poweroff
					?
					# CPU ??? ??? ???? ??? ???????
					$ sudo systemctl halt
					?
					# ??????? ?????? ????
					$ sudo systemctl suspend
					?
					# ????????? ???????? ???????? ?????? ????
					$ sudo systemctl hibernate
					?
					# ????????? ?????????????? ????? ???? ?????? ????
					$ sudo systemctl hybrid-sleep
					?
					# ?????? ???????? ?????? ???? (??? ??????????? ????????)
					
						$ sudo systemctl rescue

3.2 systemd-analyze

systemd-analyze ????????? ???? ????? ???? ???????


xxxxxxxxxx
				
				
				
				
					
						
						
						# ???? ???? ?????
					
					
						$ systemd-analyze ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 
					
					# ??????? ???????? ???? ?????? ???? ?????
					$ systemd-analyze blame
					?
					# ?????????? ??? ?????? ??????????? ?????? ????????
					$ systemd-analyze critical-chain
					?
					????????? ???????? ???? ?????? ?????
					
						$ systemd-analyze critical-chain atd.service

3.3 hostnamectl

hostnamectl ??? ??????? ??????? ???? ????? ??????? ???????


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						# ??????? ??????? ???? ?????
					
					$ hostnamectl
					?
					# ???????? ??? ?????
					
						$ sudo hostnamectl set-hostname rhel7

3.4 localectl

localectl ????????????? ?????? ????? ???? ???????


xxxxxxxxxx
				
				
				
				
					
						
						
						# ??????????? ?????? ?????
					
					$ localectl
					?
					# ????????????? ??????????? ??? ?????
					$ sudo localectl set-locale LANG=en_GB.utf8
					
						$ sudo localectl set-keymap en_GB

3.5 timedatectl

timedatectl ??????? ???? ????? ?????? ????? ???????


# ??????? ???? ????? ?????? ?????
				
				$ timedatectl
				?
				# ????? ?????? ???? ????? ?????
				
					$ timedatectl list-timezones ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 
				
				# ??????? ???? ????? ??? ????
				$ sudo timedatectl set-timezone America/New_York
				$ sudo timedatectl set-time YYYY-MM-DD
				$ sudo timedatectl set-time HH:MM:SS

3.6 loginctl

loginctl ??????? ?? ?? ??? ?????????????? ????? ???? ???????


xxxxxxxxxx
				
				
				
				
					
						
						
						# ??????? ???? ?????? ????
					
					$ loginctl list-sessions
					?
					??????? ???? ??? ?????????????? ?????? ????
					$ loginctl list-users
					?
					????????? ???????????? ???? ???????? ?????
					$ loginctl show-user ruanyf

???, ?????

?.? ????

Systemd ????? ??????? ????? ???????? ???? ????? ????? ????? ??????? ???????? ????? (Unit) ??? ????

????? ??? 12 ????? ???????

??????? ?????: ??????? ???????
?????? ?????: ?????? ??????? ???????? ???? ???? ?????
?????? ?????: ???????????? ??????
?????? ?????: ???? ????????? ?????? ???????
????????? ?????：???????????? ?????? ???????
?? ?????: ???? ?? ??
????? ?????: ???????? ?????? ????? ??? ??? ?????? ??????????
Slice Unit: ?????????? ?????
????????? ?????: ???????? ?????????, ???? ?????????? ???? ?????? ?????
???? ?????: ??????????? ????? ????????? ????
??????? ?????: ??????? ????
?????? ?????：??????

systemctl list-units ?????? ??????? ????????? ?? ????? ????? ?????


xxxxxxxxxx
				
				
				
				
					
						
						
						# ????? ????????? ?????? ????
					
					$ systemctl list-units
					?
					# ????? ????? ??????????? ????, ??? ????? ?????????? ???? ?????? ?????? ?? ???? ??? ?????? ???????
					$ systemctl list-units --all
					?
					# ????? ????? ??????? ?????? ???? ????
					$ systemctl list-units --all --state=inactive
					?
					# ????? ??? ?????? ????? ?????? ????
					$ systemctl list-units --failed
					?
					# ????? ?????, service ????? ????? ??????????? ????
					$ systemctl list-units --type=service

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

systemctl status ???????? ????????? ?????? ??? ???? ??? ??????? ?????? ????? ??????? ????


xxxxxxxxxx
				
				
				
				
					
						
						
						# ????????? ?????? ???????? ????
					
					$ systemctl status
					?
					# ???? ??????? ?????? ???????? ????
					$ sysystemctl status bluetooth.service
					?
					???????? ??????? ???? ??????? ?????? ???????? ?????
					$ systemctl -H root@rhel7.example.com status httpd.service

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


xxxxxxxxxx
				
				
				
				
					
						
						
						# ???? ????? ????? ?? ?? ?? ?????
					
					$ systemctl is-active application.service
					?
					# ???? ????? ?? ???? ?????? ???????? ??? ?? ???????? ????
					$ systemctl is-failed application.service
					?
					# ???? Unit ????? ???? ??????? ????? ???? ?????? ?? ?? ?? ?????
					$ systemctl is-enabled application.service

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

?????????????? ????, ??????? ?????? ?????????? ???? ?????? ??????, ?? ????? (???? ???????) ???? ??? ???? ???? ???? ??????? ????


xxxxxxxxxx
				
				
				
				
					
						
						
						# ???? ??????? ?????????????? ???? ????
					
					$ sudo systemctl start apache.service
					?
					# ???? ??????? ???????? ???? ????
					$ sudo systemctl stop apache.service
					?
					# ???? ??????? ??????? ???? ????
					$ sudo systemctl restart apache.service
					?
					# ???? ????????? ????? ???-?????????? ????? ????
					$ sudo systemctl kill apache.service
					?
					???? ???????? ?????????? ???? ??????? ??? ????
					$ sudo systemctl reload apache.service
					?
					# ?? ????????? ?????????? ???? ??????? ??? ????
					$ sudo systemctl daemon-reload
					?
					???? ??????? ????? ????? ??????????? ?????
					$ systemctl show httpd.service
					?
					???? ??????? ????????? ????? ??? ???????? ?????
					$ systemctl show -p CPUShares httpd.service
					?
					# ????????? ??????? ????????? ????????? ??? ???
					$ sudo systemctl set-property httpd.service CPUShares=500

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

?????????? ????? ??????????? ??????: A B ?? ??? ?????? ???, ?? ???? ?? ?? Systemd ??? A ???? ???, ??? ??? ??? ???? B-? ???? ?????

systemctl list-dependencies ???? ??????? ????? ???????????? ??????????? ???? ???????


xxxxxxxxxx
				
				
				
				
					
						
						
						$ systemctl list-dependencies nginx.service

????? ???????? ??????? ???? ???????????? ??????? ???????? (???? ????????? ?????), ?? ?????????? ????????? ??? ??? ??? ??????????? ????? ???, ????? ?????? ??????? ???? ??? --all ????????????


xxxxxxxxxx
				
				
				
				
					
						
						
						$ systemctl list-dependencies --all nginx.service

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

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

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

Systemd ?????????? ????????? ???? /etc/systemd/system/ ?????????? ???? ?????? ???, ?? ????? ???? ??????? ????? ???? ?????????? ???? ??????? ??? ???????? ?????? /usr/lib/systemd/system/ ???? ?????????? ?????? ??? ??????????? ???? ???????

systemctl enable ?? ???????? ????? ???? ?????????? ????? ???? ??????? ????? ??????? ?????? ???? ??????? ????


xxxxxxxxxx
				
				
				
				
					
						
						
						$ sudo systemctl enable clamd@scan.service
					
					# ???? ????
					$ sudo ln -s '/usr/lib/systemd/system/clamd@scan.service' '/etc/systemd/system/multi-user.target.wants/clamd@scan.service'

??? ?????????? ????? ??? ???? ???? ???? ???? ???? ??? ??? ????, systemctl enable ????????? ??????? ???? ???? ???? ??????? ????

?? ???? ??????????????, systemctl disable ???? ?????????? ????? ???? ?????????? ????? ???????? ????? ??????? ????? ???? ???? ??????, ?? ??? ????????? ????? ???? ?????


xxxxxxxxxx
				
				
				
				
					
						
						
						$ sudo systemctl disable clamd@scan.service

?????????? ?????? ????????? ?? ??? ??????? ??????, ???? sshd.socket ??? ??? ?????? ???, Systemd ?? ?????? ???? ??? ?? .service ????? sshd ???? ??? sshd.service 。

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

systemctl list-unit-files ?????? ????? ?????????? ???? ??????????? ???? ??????? ????


xxxxxxxxxx
				
				
				
				
					
						
						
						# ????? ?????????? ???? ??????????? ????
					
					$ systemctl list-unit-files
					?
					????????? ????? ?????????? ???????? ??????????? ????
					$ systemctl list-unit-files --type=service

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


xxxxxxxxxx
			
			
			
			
				
					
					
					$ systemctl list-unit-files
				
				?
				UNIT FILE ? ? ? ? ? ?  STATE
				chronyd.service ? ? ?  enabled
				clamd@.service ? ? ? ? static
				clamd@scan.service ? ? disabled

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

?????: ???? ????? ?????????? ??????
?????: ???? ???? ????? ???? ?????
?????????: ?? ?????????? ???? ??? [Install] ??? (??????? ??? ???? ??), ????????? ???????? ?????????? ?????? ?????????? ??????? ??? ???? ?????
??????: ?? ?????????? ?????? ????????? ????? ???? ???? ????????

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


xxxxxxxxxx
				
				
				
				
					
						
						
						$ systemctl status bluetooth.service

????? ?????????? ???? ???????? ???? ??, SystemD-?? ?????????? ???? ??????? ??? ???? ??? ??? ????? ??????? ???? ???? ???, ???????? ???????? ??????? ??? ???


xxxxxxxxxx
				
				
				
				
					
						
						
						$ sudo systemctl daemon-reload
					
					$ sudo systemctl restart httpd.service

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

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

systemctl cat ????????? ?????????? ?????? ?????????? ????? ?????


xxxxxxxxxx
				
				
				
				
					
						
						
						$ systemctl cat atd.service
					
					?
					[Unit]
					Description=ATD daemon
					?
					[Service]
					Type=forking
					ExecStart=/usr/bin/atd
					?
					[Install]
					WantedBy=multi-user.target

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

??????? ?????? ????????? ???? ???? ????? ?????? ??????? ??-????? ???? ???????


xxxxxxxxxx
				
				
				
				
					
						
						
						[Section]
					
					Directive1=value
					Directive2=value
					?
					. . .

5.4 ?????????? ?????? ????

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

Dsecription ????????? ??????
Documentation ?????????? ??????
Requires ??????? ??????? ????????? ???????? ????? ??? ???? ?? ????, ????? ??????? ????? ???? ??? ?????? ????
Wants ??????? ??????? ???? ??????? ???????? ?????????, ??? ?????? ????? ?? ????, ??? ??????? ??????? ?????????? ???? ??? ???
BindsTo ??? Requires ??? ?????? ??? ?? ????????? ????? ??? ???? ???? ????, ????? ??????? ????? ??? ??? ???? ??? ?????
Before ??? ????????? ????????? ?????? ???? ???? ???, ??? ??? ??????? ??????? ??? ???? ???? ????
After ??? ?? ????????? ????????? ?????? ???? ???? ???, ????? ??? ??????? ??????? ??? ???? ???? ????
Conflicts ????? ????????? ??????? ??????? ??????? ???? ?????? ?????? ???? ???
Condition... ??????? ????? ??????? ???? ??????????? ???????? ???? ???? ???, ???????? ??? ???? ???
Assert... ??????? ??????? ???? ???? ?? ???????? ???? ???? ???, ?? ?? ??? ??? ???? ??? ?????? ????

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

WantedBy ?? ??? ???? ?? ?????? ???????, ??????? ????? ??????? ??? (???????) ?????? ????? ?????? ??? ???? /etc/systemd/system ???? ???? ?????? ??????? ??? + .wants ????????? ???? ??????? ?????
RequiredBy ?? ??? ???? ?? ?????? ???????, ??????? ????? ??????? ?????????, ???????? ????????? ???? ???? /etc/systemd/system ???? ???? ?????? ??????? ??? + .required ????????? ???? ??????? ?????
Alias ??????? ??????? ???? ?????? ???? ???? ?????
Also ??????? ????? ??????? (?????) ???, ??? ???? ??????? ????? ???????? ??????

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

Type ???? ???? ???? ??????????? ???? ?????????? ????? ?? ?????????? ??????? ??? ???????
Type=simple ?????? ???, ??????? ???? ExecStart ????????? ??????, ?????? ?????????? ???? ?????
Type=forking : ????????? ?????????? ???? ???? ???????? ???? ???? ?????????? ???? ??? ???, ???? ?????? ?? ???????? ?????????? ????????????? ??? ???? ?????
Type=oneshot ??? ??????????, Systemd ??????? ??????? ??? ????? ??????? ??????? ????, ????? ??????? ????????? ??????? ?????
Type=dbus ??????? ???? D-Bus ?? ??????? ???? ????
Type=notify ??????? ???? ???? ???? ????, ?????? ???? Systemd ??? ??????? ????
Type=idle ??? ???? ???? ??? ??????? ???, ???? ??????? ??????? ???? ????
ExecStart ??????? ?????? ???? ???? ??????
ExecStartPre ??????? ??????? ???? ???? ??? ????????? ??????
ExecStartPost ??????? ???? ???? ???? ?? ??????? ??? ??? ??? ????
ExecReload ??????? ????????? ??????? ???? ???? ???? ??????? ??? ??? ??? ??????
ExecStop ??????? ??????? ???? ???? ???? ???????? ??????
ExecStopPost : ??????? ???? ???? ??? ??????? ??? ???? ???? ????
RestartSec ??????? ????? ???????????? ??????? ???? ???? ???? ???????? (????????)
Restart ??? ??????????? Systemd ???????????????? ??????? ??????? ??????? ???? ????, ???????? ??? ???????????: always (?????? ?????????) on-success 、 on-failure 、 on-abnormal 、 on-abort 、 on-watchdog
TimeoutSec Systemd ??????? ??????? ???? ???? ??? ??????? ???? ????????? ?????? ?????????? ?????
Environment ????????? ?????? ???????????

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

???, ??????

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

簡(jiǎn)單說(shuō)，Target 就是一個(gè) Unit 組，包含許多相關(guān)的 Unit 。啟動(dòng)某個(gè) Target 的時(shí)候，Systemd 就會(huì )啟動(dòng)里面所有的 Unit。從這個(gè)意義上說(shuō)，Target這個(gè)概念類(lèi)似于"狀態(tài)點(diǎn)"，啟動(dòng)某個(gè) Target 就好比啟動(dòng)到某種狀態(tài)。

??????? init ????????? ????, RunLevel ?? ????? ???, ?? Target ?? ??????????? ???? ???? ????????????? ???????? ???, RunLevel ????????????? ??? ????? ??? ????, ?????? RunLevel ?????? ???? ??? ???? ??, ?????? ?????? Target ?????? ???? ??? ?????


xxxxxxxxxx
				
				
				
				
					
						
						
						# ??????? ????????? ?? ??????? ?????
					
					$ systemctl list-unit-files --type=target
					?
					# ???? ?????? ??????????? ????? ????? ?????
					$ systemctl list-dependencies multi-user.target
					?
					# ???? ???? ???? ?????? ??????? ?????
					$ systemctl get-default
					?
					# ????? ???? ?????? ?????? ??? ????
					$ sudo systemctl set-default multi-user.target
					?
					# ??????? ???????? ???? ????, ?????????? ????????? ???? ??? ?????????? ?????????? ???? ??? ??,
					# systemctl isolate ?????? ?? ???? ???????? ???,
					# ??????? ????????? ????? ?? ?????????? ???? ???? ?? ???? ????????? ??????????? ???
					$ sudo systemctl isolate multi-user.target

Target ??? ??????? RunLevel ?? ????? ??????? ????????:


xxxxxxxxxx
				
				
				
				
					
						
						
						Traditional runlevel ? ?  New target name ? ? Symbolically linked to...
					
					?
					Runlevel 0 ? ? ? ? ? | ?  runlevel0.target -> poweroff.target
					Runlevel 1 ? ? ? ? ? | ?  runlevel1.target -> rescue.target
					Runlevel 2 ? ? ? ? ? | ?  runlevel2.target -> multi-user.target
					Runlevel 3 ? ? ? ? ? | ?  runlevel3.target -> multi-user.target
					Runlevel 4 ? ? ? ? ? | ?  runlevel4.target -> multi-user.target
					Runlevel 5 ? ? ? ? ? | ?  runlevel5.target -> graphical.target
					Runlevel 6 ? ? ? ? ? | ?  runlevel6.target -> reboot.target

??? ???? init ??????????? ?????? ???????????? ?????????

?????? ???????? (???) /etc/inittab ???? ??????) ??? ?????? ??????? ?????? ???????????? ??????, ??????? ?? /etc/systemd/system/default.target ??????? ????????? ??????? ??? graphical.target (????????? ?????????) ???? multi-user.target (??? ??????????? ?????? ????)

(?) ????????? ???? ???? ??????? ??? ??? /etc/init.d ?????????, ??????? ??? ????? ??????????? ???????? ????? (???? /etc/rc3.d 、 /etc/rc5.d ??? ??? ???????? ??? /lib/systemd/system ??? /etc/systemd/system ???????????

(?) ?????????? ?????? ??????? ??? init ??????????? ?????????? ???? ?? /etc/inittab ??????? ???????? ?????????? ???????? ???????? ???? /etc/sysconfig ????? ???????? ?????????? ???????? ??????? ???????? ?????? /lib/systemd ??????, ????? /etc/systemd ?????????? ????? ???????????? ??? ???????? ???????? ???? ?????

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

Systemd ????? ??????? ??????? ?? ??????????? ???????? ???? ?? ??? ?????? ???, ???? ????????? journalctl ???? ??????, ????? ?? ????? ???? (?????? ?? ??? ???????????? ??)? ???? ?????????? ???? ?? /etc/systemd/journald.conf 。

journalctl ?????????, ??????? ???? ???? ????? ???????


# ????? ?? ????? (??????????, ????????? ?? ???? ????? ?? ??????? ??? ???)
				
				$ sudo journalctl
				?
				# ??????? ?? ????? (???????????? ?? ???????? ?? ???)
				$ sudo journalctl -k
				?
				# ????????? ?? ??? ???? ?????? ?? ?????
				$ sudo journalctl -b
				$ sudo journalctl -b -0
				?
				# ?????????? ???? ?????? ?? ????? (?????? ???????? ???? ???)
				$ sudo journalctl -b -1
				?
				# ????????? ?????? ?? ?????
				$ sudo journalctl --since="2012-10-30 18:17:16"
				$ sudo journalctl --since "20 min ago"
				$ sudo journalctl --since yesterday
				$ sudo journalctl --since "2015-01-10" --until "2015-01-11 03:00"
				$ sudo journalctl --since 09:00 --until "1 hour ago"
				?
				# ????? 10?? ???? ?? ?????
				$ sudo journalctl -n
				?
				# ???? ????? ????????? ?????? ???? ?????
				$ sudo journalctl -n 20
				?
				# ??????? ?????? ?????? ????? ????????? ??? ?????
				$ sudo journalctl -f
				?
				# ????????? ???????? ?? ?????
				$ sudo journalctl /usr/lib/systemd/systemd
				?
				# ????????? ??????????? ?? ?????
				$ sudo journalctl _PID=1
				?
				# ???? ???? ??????????? ?? ?????
				$ sudo journalctl /usr/bin/bash
				?
				????????? ???????????? ?? ?????
				$ sudo journalctl _UID=33 --since today
				?
				# ???? ??????? ?? ?????
				$ sudo journalctl -u nginx.service
				$ sudo journalctl -u nginx.service --since today
				?
				# ???? ??????? ??????? ?????? ?????? ????? ????? ??????
				$ sudo journalctl -u nginx.service -f
				?
				?????? ??????? ?? ??????? ??? ???????? ?????
				$ journalctl -u nginx.service -u php-fpm.service --since today
				?
				????????? ?????????? (??? ?? ????? ????) ?? ?? ?????, ??? 8 ???? ??????
				# 0: emerg
				# 1: alert
				# 2: crit
				# 3: err
				# 4: warning
				# 5: notice
				# 6: info
				
					# 7: debug
				
				$ sudo journalctl -p err -b
				
					?
				
				# ?? ?????? ???????? ??????, --no-pager ????????? ????? ??????? ???????? ????
				$ sudo journalctl --no-pager
				?
				{"翻譯結果":"JSON ???????? (?? ?????) ?????? ????"}
				$ sudo journalctl -b -u nginx.service -o json
				?
				```json
{
  "翻譯": "JSON ???????? (?????? ????) ?????? ????, ?? ??? ????? ??????????"
}
```
				$ sudo journalctl -b -u nginx.serviceqq
				-o json-pretty
				?
				# ?? ???? ?????? ?????? ????? ????? ???????? ????
				$ sudo journalctl --disk-usage
				?
				?? ?????? ???????? ????? ???????? ????
				$ sudo journalctl --vacuum-size=1G
				
					?
				
				# ?? ???? ??????? ????? ???
				$ sudo journalctl --vacuum-time=1years

(??????)

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

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

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

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

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

??. ???

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

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

3.1 systemctl

3.2 systemd-analyze

3.3 hostnamectl

3.4 localectl

3.5 timedatectl

3.6 loginctl

???, ?????

?.? ????

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

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

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

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

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

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

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

5.4 ?????????? ?????? ????

???, ??????

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

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

BeJSON ????????? ????????

JSON ???

?????/?????????

??????? ???

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BeJSON ??????? QQ ?????