CNI online course - systemd 小記

systemd

Location:  /usr/lib/systemd/system/  and  /etc/systemd/system/

設定範例

# cat   /usr/lib/systemd/system/sshd.service

[Unit]

Description=OpenSSH Daemon

After=network.target

[Service]

EnvironmentFile=/etc/sysconfig/ssh

ExecStartPre=/usr/sbin/sshd-gen-keys-start

ExecStart=/usr/sbin/sshd -D $SSHD_OPTS

ExecReload=/bin/kill -HUP $MAINPID

KillMode=process

Restart=always

[Install]

WantedBy=multi-user.target

systemctl   mask    <service>.service

• mask 只要使用, 不可以手動啟動服務
• unmask 取消mask

查詢的方式 ( 該服務會被導向到 /dev/null  )

# ls   -l   /etc/systemd/system | grep null

以類型來列出

# systemctl  -t  service

# systemctl  -t  service | grep ssh

sshd.service                       loaded active running OpenSSH Daemon

有些 target 可以跟 runlevel 對照

Target units group service and other units

Some target units are the equivalent to runlevels

• multi-user.target - runlevel 3
• graphical.target - runlevel 5

# systemctl  -t  target

UNIT                 LOAD   ACTIVE SUB    DESCRIPTION

basic.target         loaded active active Basic System

cryptsetup.target    loaded active active Encrypted Volumes

getty.target         loaded active active Login Prompts

graphical.target     loaded active active Graphical Interface

開機的時候可以在 linux 那一行指定 target 來暫時切換target ( runlevel )

例如原本是圖形界面, 開機要指定文字界面開機

systemd.unit=multi-user.target

開機以文字界面(runlevel 3) 開機, 但是如果想切換圖形界面

可以更改 target 來達成 ( 當然目前還可以用 init 切換 )

#systemctl  isolate  graphical.target

開機時間

# systemd-analyze

Startup finished in 2.739s (kernel) + 17.430s (userspace) = 20.170s

詳細的列出

# systemd-analyze  blame

        11.260s network.service

         8.133s network@ens160.service

         2.104s ModemManager.service

         2.050s SuSEfirewall2_init.service

         1.658s network@ens192.service

         1.522s rsyslog.service

          974ms vmtoolsd.service

SLES 12 跟 openSUSE 13.2 一樣用 systemd-logger 取代 syslog-ng

Systemd has an internal log daemon – journald

透過導向的方式存檔

journalctl  >  file.txt

systemd and cgroups

• Each service is placed into a cgroup in  /sys/fs/cgroup/systemd/system.slice
• systemd uses this directory to control services, not for resource control

See man systemd.resource­control for available options

檢查相關資訊

# systemd-cgls

Working Directory /sys/fs/cgroup/systemd/system.slice:

├─1 /sbin/init showopts

├─polkit.service

│ └─18657 /usr/lib/polkit-1/polkitd --no-debug

├─accounts-daemon.service

│ └─18652 /usr/lib/accounts-daemon

├─system-network.slice

│ ├─network@ens192.service

│ │ ├─1955 avahi-autoipd: [ens192] sleeping  

│ │ └─1956 avahi-autoipd: [ens192] callout dispatche

│ └─network@ens160.service

│   ├─1518 avahi-autoipd: [ens160] sleeping  

│   └─1519 avahi-autoipd: [ens160] callout dispatche