systemctl 命令詳解及使用教程
在本教程中, 我們將向您介紹在運行 systemd 的 linux 系統上如何使用 systemctl 命令工具有效的控制系統和服務.
Systemctl 介紹
Systemctl 是一個 systemd 工具，主要負責控制 systemd 系統和服務管理器。
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準 Linux 發行版中，只有爲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，但並非總是如此。
開始 Systemd 和 Systemctl 基礎工具之旅
01、首先檢查系統上是否安裝了 systemd 以及當前安裝的 Systemd 的版本是什麼？
# systemd --version
systemd 215
+PAM +AUDIT +SELINUX +IMA +SYSVINIT +LIBCRYPTSETUP +GCRYPT +ACL +XZ -SECCOMP -APPARMOR從上面的例子可以清楚地看出，我們已經安裝了 systemd 215 版本。
- 檢查 systemd 和 systemctl 的二進制文件和庫的安裝位置。
# whereis systemd
systemd: /usr/lib/systemd /etc/systemd /usr/share/systemd /usr/share/man/man1/systemd.1.gz
# whereis systemctl
systemctl: /usr/bin/systemctl /usr/share/man/man1/systemctl.1.gz- 檢查 systemd 是否正在運行。
# ps -eaf | grep [s]ystemd
root 1 0 0 16:27 ? 00:00:00 /usr/lib/systemd/systemd --switched-root --system --deserialize 23
root 444 1 0 16:27 ? 00:00:00 /usr/lib/systemd/systemd-journald
root 469 1 0 16:27 ? 00:00:00 /usr/lib/systemd/systemd-udevd
root 555 1 0 16:27 ? 00:00:00 /usr/lib/systemd/systemd-logind
dbus 556 1 0 16:27 ? 00:00:00 /bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation注意：systemd 作爲父守護進程運行（PID = 1）。 在上面的命令 ps 中使用（-e）選擇所有進程，（ - a）選擇除會話前導之外的所有進程和（-f）選擇完整格式列表（即 - eaf）。
另請注意上面示例中的方括號以及其他示例。 Square Bracket 表達式是 grep 的字符類模式匹配的一部分。
- 分析 systemd 啓動過程
# systemd-analyze
Startup finished in 487ms (kernel) + 2.776s (initrd) + 20.229s (userspace) = 23.493s- 分析每個進程在引導時花費的時間
# systemd-analyze blame
8.565s mariadb.service
7.991s webmin.service
6.095s postfix.service
4.311s httpd.service
3.926s firewalld.service
3.780s kdump.service
3.238s tuned.service
1.712s network.service
1.394s lvm2-monitor.service
1.126s systemd-logind.service
....- 分析啓動時的關鍵鏈
# 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.
multi-user.target @20.222s
└─mariadb.service @11.657s +8.565s
└─network.target @11.168s
└─network.service @9.456s +1.712s
└─NetworkManager.service @8.858s +596ms
└─firewalld.service @4.931s +3.926s
└─basic.target @4.916s
└─sockets.target @4.916s
└─dbus.socket @4.916s
└─sysinit.target @4.905s
└─systemd-update-utmp.service @4.864s +39ms
└─auditd.service @4.563s +301ms
└─systemd-tmpfiles-setup.service @4.485s +69ms
└─rhel-import-state.service @4.342s +142ms
└─local-fs.target @4.324s
└─boot.mount @4.286s +31ms
└─systemd-fsck@dev-disk-by\x2duuid-79f594ad\x2da332\x2d4730\x2dbb5f\x2d85d19608096
└─dev-disk-by\x2duuid-79f594ad\x2da332\x2d4730\x2dbb5f\x2d85d196080964.device @4重要：Systemctl 接受服務（.service），掛載點（.mount），套接字（.socket）和設備（.device）作爲單位。
07、列出所有可用的單位
systemctl list-unit-files
UNIT FILE STATE
proc-sys-fs-binfmt_misc.automount static
dev-hugepages.mount static
dev-mqueue.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
brandbot.path disabled
.....08、列出所有運行單元
# systemctl list-units
UNIT LOAD ACTIVE SUB DESCRIPTION
proc-sys-fs-binfmt_misc.automount loaded active waiting Arbitrary Executable File Formats File Syste
sys-devices-pc...0-1:0:0:0-block-sr0.device loaded active plugged VBOX_CD-ROM
sys-devices-pc...:00:03.0-net-enp0s3.device loaded active plugged PRO/1000 MT Desktop Adapter
sys-devices-pc...00:05.0-sound-card0.device loaded active plugged 82801AA AC'97 Audio Controller
sys-devices-pc...:0:0-block-sda-sda1.device loaded active plugged VBOX_HARDDISK
sys-devices-pc...:0:0-block-sda-sda2.device loaded active plugged LVM PV Qzyo3l-qYaL-uRUa-Cjuk-pljo-qKtX-VgBQ8
sys-devices-pc...0-2:0:0:0-block-sda.device loaded active plugged VBOX_HARDDISK
sys-devices-pl...erial8250-tty-ttyS0.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS0
sys-devices-pl...erial8250-tty-ttyS1.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS1
sys-devices-pl...erial8250-tty-ttyS2.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS2
sys-devices-pl...erial8250-tty-ttyS3.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS3
sys-devices-virtual-block-dm\x2d0.device loaded active plugged /sys/devices/virtual/block/dm-0
sys-devices-virtual-block-dm\x2d1.device loaded active plugged /sys/devices/virtual/block/dm-1
sys-module-configfs.device loaded active plugged /sys/module/configfs
...09、列出所有失敗的單元
# systemctl --failed
UNIT LOAD ACTIVE SUB DESCRIPTION
kdump.service loaded failed failed Crash recovery kernel arming
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.
1 loaded units listed. Pass --all to see loaded but inactive units, too.
To show all installed unit files use 'systemctl list-unit-files'.10、檢查單元 (cron.service) 是否啓用?
# systemctl is-enabled crond.service
enabled- 檢查單元或服務是否正在運行？
systemctl status firewalld.service
firewalld.service - firewalld - dynamic firewall daemon
Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled)
Active: active (running) since Tue 2018-04-28 16:27:55 IST; 34min ago
Main PID: 549 (firewalld)
CGroup: /system.slice/firewalld.service
└─549 /usr/bin/python -Es /usr/sbin/firewalld --nofork --nopid
Apr 28 16:27:51 tecmint systemd[1]: Starting firewalld - dynamic firewall daemon...
Apr 28 16:27:55 tecmint systemd[1]: Started firewalld - dynamic firewall daemon.- 列出所有服務（包括啓用和禁用）
# systemctl list-unit-files --type=service
UNIT FILE STATE
arp-ethers.service disabled
auditd.service enabled
autovt@.service disabled
blk-availability.service disabled
brandbot.service static
collectd.service disabled
console-getty.service disabled
console-shell.service disabled
cpupower.service disabled
crond.service enabled
dbus-org.fedoraproject.FirewallD1.service enabled
....- 如何在 Linux 中啓動，重新啓動，停止，重新加載和檢查服務（httpd.service）的狀態
# systemctl start httpd.service
# systemctl restart httpd.service
# systemctl stop httpd.service
# systemctl reload httpd.service
# systemctl status httpd.service
httpd.service - The Apache HTTP Server
Loaded: loaded (/usr/lib/systemd/system/httpd.service; enabled)
Active: active (running) since Tue 2018-04-28 17:21:30 IST; 6s ago
Process: 2876 ExecStop=/bin/kill -WINCH ${MAINPID} (code=exited, status=0/SUCCESS)
Main PID: 2881 (httpd)
Status: "Processing requests..."
CGroup: /system.slice/httpd.service
├─2881 /usr/sbin/httpd -DFOREGROUND
├─2884 /usr/sbin/httpd -DFOREGROUND
├─2885 /usr/sbin/httpd -DFOREGROUND
├─2886 /usr/sbin/httpd -DFOREGROUND
├─2887 /usr/sbin/httpd -DFOREGROUND
└─2888 /usr/sbin/httpd -DFOREGROUND
Apr 28 17:21:30 tecmint systemd[1]: Starting The Apache HTTP Server...
Apr 28 17:21:30 tecmint httpd[2881]: AH00558: httpd: Could not reliably determine the server's fully q...ssage
Apr 28 17:21:30 tecmint systemd[1]: Started The Apache HTTP Server.
Hint: Some lines were ellipsized, use -l to show in full.注意：當我們使用 systemctl 等啓動，重啓，停止和重載等命令時，我們將不會在終端上獲得任何輸出，只有 status 命令會打印輸出。
- 如何在引導時激活服務並啓用或禁用服務（系統引導時自動啓動服務）
# systemctl is-active httpd.service
# systemctl enable httpd.service
# systemctl disable httpd.service- 如何屏蔽（使其無法啓動）或取消屏蔽服務（httpd.service)
ln -s '/dev/null' '/etc/systemd/system/httpd.service'
# systemctl unmask httpd.service
rm '/etc/systemd/system/httpd.service'- 如何使用 systemctl 命令終止服務
# systemctl kill httpd
# systemctl status httpd
httpd.service - The Apache HTTP Server
Loaded: loaded (/usr/lib/systemd/system/httpd.service; enabled)
Active: failed (Result: exit-code) since Tue 2018-04-28 18:01:42 IST; 28min ago
Main PID: 2881 (code=exited, status=0/SUCCESS)
Status: "Total requests: 0; Current requests/sec: 0; Current traffic: 0 B/sec"
Apr 28 17:37:29 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.
Apr 28 17:37:29 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.
Apr 28 17:37:39 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.
Apr 28 17:37:39 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.
Apr 28 17:37:49 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.
Apr 28 17:37:49 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.
Apr 28 17:37:59 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.
Apr 28 17:37:59 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.
Apr 28 18:01:42 tecmint systemd[1]: httpd.service: control process exited, code=exited status=226
Apr 28 18:01:42 tecmint systemd[1]: Unit httpd.service entered failed state.
Hint: Some lines were ellipsized, use -l to show in full.使用 Systemctl 控制和管理掛載點
- 列出所有系統安裝點
# systemctl list-unit-files --type=mount
UNIT FILE STATE
dev-hugepages.mount static
dev-mqueue.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- 如何裝載，卸載，重新裝載，重新裝載系統裝載點，以及檢查系統上裝載點的狀態
# systemctl start tmp.mount
# systemctl stop tmp.mount
# systemctl restart tmp.mount
# systemctl reload tmp.mount
# systemctl status tmp.mount
tmp.mount - Temporary Directory
Loaded: loaded (/usr/lib/systemd/system/tmp.mount; disabled)
Active: active (mounted) since Tue 2018-04-28 17:46:06 IST; 2min 48s ago
Where: /tmp
What: tmpfs
Docs: man:hier(7)
http://www.freedesktop.org/wiki/Software/systemd/APIFileSystems
Process: 3908 ExecMount=/bin/mount tmpfs /tmp -t tmpfs -o mode=1777,strictatime (code=exited, status=0/SUCCESS)
Apr 28 17:46:06 tecmint systemd[1]: Mounting Temporary Directory...
Apr 28 17:46:06 tecmint systemd[1]: tmp.mount: Directory /tmp to mount over is not empty, mounting anyway.
Apr 28 17:46:06 tecmint systemd[1]: Mounted Temporary Directory.- 如何在引導時激活，啓用或禁用裝入點（在系統引導時自動裝入）
# systemctl is-active tmp.mount
# systemctl enable tmp.mount
# systemctl disable tmp.mount- 如何在 Linux 中屏蔽（使其無法啓動）或取消屏蔽掛載點
# systemctl mask tmp.mount
ln -s '/dev/null' '/etc/systemd/system/tmp.mount'
# systemctl unmask tmp.mount
rm '/etc/systemd/system/tmp.mount'使用 Systemctl 控制和管理套接字
- 列出所有可用的系統套接字。
# systemctl list-unit-files --type=socket
UNIT FILE STATE
dbus.socket static
dm-event.socket enabled
lvm2-lvmetad.socket enabled
rsyncd.socket disabled
sshd.socket disabled
syslog.socket static
systemd-initctl.socket static
systemd-journald.socket static
systemd-shutdownd.socket static
systemd-udevd-control.socket static
systemd-udevd-kernel.socket static
11 unit files listed.- 如何在 Linux 中啓動，重新啓動，停止，重新加載和檢查套接字的狀態（例如：cups.socket）
# systemctl start cups.socket
# systemctl restart cups.socket
# systemctl stop cups.socket
# systemctl reload cups.socket
# systemctl status cups.socket
cups.socket - CUPS Printing Service Sockets
Loaded: loaded (/usr/lib/systemd/system/cups.socket; enabled)
Active: active (listening) since Tue 2015-04-28 18:10:59 IST; 8s ago
Listen: /var/run/cups/cups.sock (Stream)
Apr 28 18:10:59 tecmint systemd[1]: Starting CUPS Printing Service Sockets.
Apr 28 18:10:59 tecmint systemd[1]: Listening on CUPS Printing Service Sockets.- 如何激活套接字並在引導時啓用或禁用（在系統引導時自動啓動套接字）
# systemctl is-active cups.socket
# systemctl enable cups.socket
# systemctl disable cups.socket- 如何屏蔽（使其無法啓動）或取消屏蔽插座（cups.socket）
# systemctl mask cups.socket
ln -s '/dev/null' '/etc/systemd/system/cups.socket'
# systemctl unmask cups.socket
rm '/etc/systemd/system/cups.socket'服務的 CPU 利用率（份額）
- 獲取服務的當前 CPU 份額（比如 httpd）
# systemctl show -p CPUShares httpd.service
CPUShares=1024注意：每個服務的默認值都爲 CPUShare = 1024. 您可以增加 / 減少進程的 CPU 份額。
- 將服務的 CPU 份額（httpd.service）限制爲 2000 CPUShares /
# systemctl set-property httpd.service CPUShares=2000
# systemctl show -p CPUShares httpd.service
CPUShares=2000注意：爲服務設置 CPUShare 時，會創建一個名爲 service 的目錄（httpd.service.d），其中包含一個包含 CPUShare Limit 信息的文件 90-CPUShares.conf。 您可以將文件視爲：
# vi /etc/systemd/system/httpd.service.d/90-CPUShares.conf
[Service]
CPUShares=2000- 檢查服務的所有配置詳細信息
# systemctl show httpd
Id=httpd.service
Names=httpd.service
Requires=basic.target
Wants=system.slice
WantedBy=multi-user.target
Conflicts=shutdown.target
Before=shutdown.target multi-user.target
After=network.target remote-fs.target nss-lookup.target systemd-journald.socket basic.target system.slice
Description=The Apache HTTP Server
LoadState=loaded
ActiveState=active
SubState=running
FragmentPath=/usr/lib/systemd/system/httpd.service
....- 分析服務的關鍵鏈（httpd）
# systemd-analyze critical-chain httpd.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.
httpd.service +142ms
└─network.target @11.168s
└─network.service @9.456s +1.712s
└─NetworkManager.service @8.858s +596ms
└─firewalld.service @4.931s +3.926s
└─basic.target @4.916s
└─sockets.target @4.916s
└─dbus.socket @4.916s
└─sysinit.target @4.905s
└─systemd-update-utmp.service @4.864s +39ms
└─auditd.service @4.563s +301ms
└─systemd-tmpfiles-setup.service @4.485s +69ms
└─rhel-import-state.service @4.342s +142ms
└─local-fs.target @4.324s
└─boot.mount @4.286s +31ms
└─systemd-fsck@dev-disk-by\x2duuid-79f594ad\x2da332\x2d4730\x2dbb5f\x2d85d196080964.service @4.092s +149ms
└─dev-disk-by\x2duuid-79f594ad\x2da332\x2d4730\x2dbb5f\x2d85d196080964.device @4.092s- 獲取服務的依賴項列表（httpd）
# systemctl list-dependencies httpd.service
httpd.service
├─system.slice
└─basic.target
├─firewalld.service
├─microcode.service
├─rhel-autorelabel-mark.service
├─rhel-autorelabel.service
├─rhel-configure.service
├─rhel-dmesg.service
├─rhel-loadmodules.service
├─paths.target
├─slices.target
│ ├─-.slice
│ └─system.slice
├─sockets.target
│ ├─dbus.socket
....- 按層次列出控制組
# systemd-cgls
├─1 /usr/lib/systemd/systemd --switched-root --system --deserialize 23
├─user.slice
│ └─user-0.slice
│ └─session-1.scope
│ ├─2498 sshd: root@pts/0
│ ├─2500 -bash
│ ├─4521 systemd-cgls
│ └─4522 systemd-cgls
└─system.slice
├─httpd.service
│ ├─4440 /usr/sbin/httpd -DFOREGROUND
│ ├─4442 /usr/sbin/httpd -DFOREGROUND
│ ├─4443 /usr/sbin/httpd -DFOREGROUND
│ ├─4444 /usr/sbin/httpd -DFOREGROUND
│ ├─4445 /usr/sbin/httpd -DFOREGROUND
│ └─4446 /usr/sbin/httpd -DFOREGROUND
├─polkit.service
│ └─721 /usr/lib/polkit-1/polkitd --no-debug
....- 根據 CPU，內存，輸入和輸出列出控制組
# systemd-cgtop
Path Tasks %CPU Memory Input/s Output/s
/ 83 1.0 437.8M - -
/system.slice - 0.1 - - -
/system.slice/mariadb.service 2 0.1 - - -
/system.slice/tuned.service 1 0.0 - - -
/system.slice/httpd.service 6 0.0 - - -
/system.slice/NetworkManager.service 1 - - - -
/system.slice/atop.service 1 - - - -
/system.slice/atopacct.service 1 - - - -
/system.slice/auditd.service 1 - - - -
/system.slice/crond.service 1 - - - -
/system.slice/dbus.service 1 - - - -
/system.slice/firewalld.service 1 - - - -
/system.slice/lvm2-lvmetad.service 1 - - - -
/system.slice/polkit.service 1 - - - -
/system.slice/postfix.service 3 - - - -
/system.slice/rsyslog.service 1 - - - -
/system.slice/system-getty.slice/getty@tty1.service 1 - - - -
/system.slice/systemd-journald.service 1 - - - -
/system.slice/systemd-logind.service 1 - - - -
/system.slice/systemd-udevd.service 1 - - - -
/system.slice/webmin.service 1 - - - -
/user.slice/user-0.slice/session-1.scope 3 - - - -控制系統運行級別
- 如何啓動系統救援模式
# systemctl rescue
Broadcast message from root@tecmint on pts/0 (Wed 2015-04-29 11:31:18 IST):
The system is going down to rescue mode NOW!- 如何進入緊急模式。
# 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 into default mode.- 列出當前使用的運行級別
# systemctl get-default
multi-user.target- 如何啓動 Runlevel 5 aka 圖形模式。
# systemctl isolate runlevel5.target
OR
# systemctl isolate graphical.target- 如何啓動 Runlevel 3 又稱多用戶模式（命令行）
# systemctl isolate runlevel3.target
OR
# systemctl isolate multiuser.target- 如何將多用戶模式或圖形模式設置爲默認運行級別
# systemctl set-default runlevel3.target
# systemctl set-default runlevel5.target- 如何重啓，暫停，暫停，休眠或將系統置於混合睡眠狀態
# systemctl reboot
# systemctl halt
# systemctl suspend
# systemctl hibernate
# systemctl hybrid-sleep對於那些可能不瞭解跑步水平及其作用的人。
-
運行級別 0：關閉並關閉系統電源。
-
運行級別 1：救援？維護模式。
-
運行級別 3：多用戶，無圖形系統。
-
運行級別 4：多用戶，無圖形系統。
-
運行級別 5：多用戶，圖形系統。
-
運行級別 6：關閉並重新啓動機器。
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來源：https://mp.weixin.qq.com/s/lQHU-Gsm9xwoKWTUOijBDw