systemctl/systemd 常用命令_/lib/systemd/systemd-logind

01.检查systemd是否正在运行。

# 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作为父守护进程运行（PID = 1）。 在上面的命令ps中使用（-e）选择所有进程，（ - a）选择除会话前导之外的所有进程和（-f）选择完整格式列表（即-eaf）。

02.列出所有可用的单位

# 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
.....

03、检查单元(cron.service)是否启用?

# systemctl is-enabled crond.service
enabled

04.检查单元或服务是否正在运行？

 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.

05.列出所有服务（包括启用和禁用）

# 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 

06.如何在Linux中启动，重新启动，停止，重新加载和检查服务（httpd.service）的状态

# 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：当我们使用systemctl等启动，重启，停止和重载等命令时，我们将不会在终端上获得任何输出，只有status命令会打印输出。

07.如何在引导时激活服务并启用或禁用服务（系统引导时自动启动服务）

# systemctl is-active httpd.service
# systemctl enable httpd.service
# systemctl disable httpd.service

实战

创建一个systemd服务

cd /etc/systemd/system

sudo nano ss2.service

ss2.service内容如下

[Unit]
Description=ss2 service
After=network.target
[Service]
Type=simple
ExecStart=/usr/bin/bash /root/sh/ss2.sh
 
[Install]
WantedBy=multi-user.target

systemctl enable ss2

systemctl start ss2

小贴士：

Service types

There are several different start-up types to consider when writing a custom service file. This is set with the Type= parameter in the [Service] section:

• Type=simple (default): systemd considers the service to be started up immediately. The process must not fork. Do not use this type if other services need to be ordered on this service, unless it is socket activated.
• Type=forking: systemd considers the service started up once the process forks and the parent has exited. For classic daemons use this type unless you know that it is not necessary. You should specify PIDFile= as well so systemd can keep track of the main process.
• Type=oneshot: this is useful for scripts that do a single job and then exit. You may want to set RemainAfterExit=yes as well so that systemd still considers the service as active after the process has exited.
• Type=notify: identical to Type=simple, but with the stipulation that the daemon will send a signal to systemd when it is ready. The reference implementation for this notification is provided by libsystemd-daemon.so.
• Type=dbus: the service is considered ready when the specified BusName appears on DBus's system bus.
• Type=idle: systemd will delay execution of the service binary until all jobs are dispatched. Other than that behavior is very similar to Type=simple.

See the systemd.service(5) § OPTIONS man page for a more detailed explanation of the Type values.