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Systemd

簡介

Linux 的各項服務管理一直都是用 SysV Init Script，Systemd 是新的管理工具，在 CentOS 7 開始已經有支援。

設定上比 SysV Init 簡單許多，指令的操作差異不大。

線上教學：

支援的 Linux：

  • CentOS 7+
  • Ubuntu 16.04+

其他類似應用：

  • Supervisor
    這個被使用在 Ubuntu 9.10，Mac OS X (10.4/10.5/10.6)，Solaris (10 for Intel) 及 FreeBSD 6.1。系統環境需要有 Python 2.4，但不支援 Python 3。

相關目錄：

  • /etc/systemd/system 客製的服務啟動檔位置
  • /lib/systemd/system 內建系統的服務啟動檔位置

服務設定檔

/etc/systemd/system/backup.service

[Unit]
Description=Backup daemon

[Service]
Type=simple
ExecStart=/path/to/backup

[Install]
WantedBy=multi-user.target

TIP:

multi-user.target 這是表示 Run Level 3

更多資訊可以前往 http://0pointer.de/blog/projects/systemd-for-admins-3.html

新增一個服務設定檔

/etc/systemd/system/freepbx.service

[Unit]
Description=Freepbx
After=mariadb.service
 
[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/usr/sbin/fwconsole start
ExecStop=/usr/sbin/fwconsole stop
 
[Install]
WantedBy=multi-user.target

將服務設為自動啟用

systemctl enable freepbx

服務管理

啟動服務

# Reload Systemd
systemctl daemon-reload

# 啟動服務
systemctl start <service-name>

# 檢查服務狀態
systemctl status <service-name>
systemctl is-active <service-name> 
systemctl is-enabled <service-name>

# 關閉服務
systemctl stop <service-name>

# 啟用:自動啟動
systemctl enable <service-name>

# 關閉:自動啟動
systemctl disable <service-name>

# 列出設為自動啟用的服務
systemctl list-unit-files --type=service --state=enabled

檢視服務清單

# list active services
systemctl list-units --type=service

# List all the running systemd services
systemctl list-units --type=service --state=running

# List all loaded systemd services including the inactive ones
systemctl list-units --all --type=service

# List all the inactive systemd services
systemctl list-units --all --type=service --state=inactive

# List all the installed systemd services
systemctl list-unit-files --type=service

# List all systemd services that will be run at each boot automatically
systemctl list-unit-files --type=service --state=enabled

關機與開機

# Halt the system
systemctl halt

# Poeroff the system
systemctl poweroff

# Reboot the system
systemctl reboot

Journalctl

檢視系統日誌

# view journal entries for time zones
journalctl --utc

# view only errors, warnings, etc in journal logs
# Error codes
# 0: emergency
# 1: alerts
# 2: critical
# 3: errors
# 4: warning
# 5: notice
# 6: info
# 7: debug
journalctl -p 0

# When you specify the error code, it shows all messages from that code and above. 
# For example, if you specify the below command, it shows all messages with priority 2, 1 and 0
journalctl -p 2

# view journal logs for a specific boot
journalctl --list-boots

# To view a specific boot number you the first number or the boot ID as below.
journalctl -b -45
journalctl -b 8bab42c7e82440f886a3f041a7c95b98

# You can also use -x switch which can add an explanation of the systemd 
# error messages in your display. This is a lifesaver in certain situations.
journalctl -xb -p 3

# view journal logs for a specific time, date duration
journalctl --since "2020-12-04 06:00:00"
journalctl --since "2020-12-03" --until "2020-12-05 03:00:00"
journalctl --since yesterday
journalctl --since 09:00 --until "1 hour ago"

# see Kernel specific journal logs
journalctl -k

# see journal logs for a service, PID
journalctl -u NetworkManager.service

# If you do not know the service name, you can use the below 
# command to list the systemd services in your system.
systemctl list-units --type=service

# view journal logs for a user, group
id -u debugpoint
journalctl _UID=1000 --since today

# view journal logs for an executable
journalctl /usr/bin/gnome-shell --since today

其他附屬指令

coredumpctl
# 列出系統所有 core dump
coredumpctl

# 列出指定 program 的 core dump
coredumpctl dump <program-name>

# 列出指定 PID
coredumpctl dump _PID=XXX

# 分析特定 core dump 的內容
coredumpctl gdb <PID>

# 預設 core dump files 路徑
/var/lib/systemd/coredump
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