CentOS7中的systemctl命令详解
systemctl 命令是系统服务管理器指令，将 service 和 chkconfig 两个命令组合到一起。systemctl 命令常用的功能如下：
一、启动、重启、停止、重载服务以及检查服务状态
以 firewalld 为例：
1、启动 firewalld 服务
[root@localhost ~]# systemctl start firewalld.service
2、停止 firewalld 服务
[root@localhost ~]# systemctl stop firewalld.service
3、重新启动 firewalld 服务
[root@localhost ~]# systemctl restart firewalld.service
4、重载 firewalld 服务
[root@localhost ~]# systemctl reload firewalld.service
5、查看 firewalld 服务状态
[root@localhost ~]# systemctl status firewalld.service
● firewalld.service - firewalld - dynamic firewall daemon
Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled; vendor preset: enabled)
Active: active (running) since Fri 2020-08-07 04:48:14 EDT; 1min 19s ago
Docs: man:firewalld(1)
Process: 1860 ExecReload=/bin/kill -HUP $MAINPID (code=exited, status=0/SUCCESS)
Main PID: 1764 (firewalld)
CGroup: /system.slice/firewalld.service
└─1764 /usr/bin/python2 -Es /usr/sbin/firewalld --nofork --nopid
Aug 07 04:48:13 localhost.localdomain systemd[1]: Starting firewalld - dynamic firewall daemon...
Aug 07 04:48:14 localhost.localdomain systemd[1]: Started firewalld - dynamic firewall daemon.
Aug 07 04:48:14 localhost.localdomain firewalld[1764]: WARNING: AllowZoneDrifting is enabled. This is considered an inse... now.
Aug 07 04:48:48 localhost.localdomain systemd[1]: Reloading firewalld - dynamic firewall daemon.
Aug 07 04:48:48 localhost.localdomain systemd[1]: Reloaded firewalld - dynamic firewall daemon.
Aug 07 04:48:48 localhost.localdomain firewalld[1764]: WARNING: AllowZoneDrifting is enabled. This is considered an inse... now.
Hint: Some lines were ellipsized, use -l to show in full.
二、开机时启用或禁用服务
1、开机时禁用 firewalld 服务
[root@localhost ~]# systemctl disable firewalld.service
Removed symlink /etc/systemd/system/multi-user.target.wants/firewalld.service.
Removed symlink /etc/systemd/system/dbus-org.fedoraproject.FirewallD1.service.
Removed symlink /etc/systemd/system/basic.target.wants/firewalld.service.
2、开机时启用 firewalld 服务
[root@localhost ~]# systemctl enable firewalld.service
Created symlink from /etc/systemd/system/dbus-org.fedoraproject.FirewallD1.service to /usr/lib/systemd/system/firewalld.service.
Created symlink from /etc/systemd/system/multi-user.target.wants/firewalld.service to /usr/lib/systemd/system/firewalld.service.
3、查看 firewalld 服务是否设置为开机启动
[root@localhost ~]# systemctl is-enabled firewalld.service
enabled
4、查看所有已经启动的服务
[root@localhost ~]# systemctl list-units --type=service
UNIT LOAD ACTIVE SUB DESCRIPTION
auditd.service loaded active running Security Auditing Service
chronyd.service loaded active running NTP client/server
crond.service loaded active running Command Scheduler
dbus.service loaded active running D-Bus System Message Bus
firewalld.service loaded active running firewalld - dynamic firewall daemon
[email protected] loaded active running Getty on tty1
● kdump.service loaded failed failed Crash recovery kernel arming
kmod-static-nodes.service loaded active exited Create list of required static device nodes for the current kernel
lvm2-lvmetad.service loaded active running LVM2 metadata daemon
lvm2-monitor.service loaded active exited Monitoring of LVM2 mirrors, snapshots etc. using dmeventd or progress
lvm2-pvscan@8:2.service loaded active exited LVM2 PV scan on device 8:2
mysqld.service loaded active running LSB: start and stop MySQL
network.service loaded active exited LSB: Bring up/down networking
NetworkManager-wait-online.service loaded active exited Network Manager Wait Online
NetworkManager.service loaded active running Network Manager
polkit.service loaded active running Authorization Manager
● postfix.service loaded failed failed Postfix Mail Transport Agent
rhel-dmesg.service loaded active exited Dump dmesg to /var/log/dmesg
rhel-domainname.service loaded active exited Read and set NIS domainname from /etc/sysconfig/network
rhel-import-state.service loaded active exited Import network configuration from initramfs
rhel-readonly.service loaded active exited Configure read-only root support
rsyslog.service loaded active running System Logging Service
sshd.service loaded active running OpenSSH server daemon
systemd-journal-flush.service loaded active exited Flush Journal to Persistent Storage
systemd-journald.service loaded active running Journal Service
systemd-logind.service loaded active running Login Service
systemd-random-seed.service loaded active exited Load/Save Random Seed
systemd-remount-fs.service loaded active exited Remount Root and Kernel File Systems
systemd-sysctl.service loaded active exited Apply Kernel Variables
systemd-tmpfiles-setup-dev.service loaded active exited Create Static Device Nodes in /dev
systemd-tmpfiles-setup.service loaded active exited Create Volatile Files and Directories
systemd-udev-trigger.service loaded active exited udev Coldplug all Devices
systemd-udevd.service loaded active running udev Kernel Device Manager
systemd-update-utmp.service loaded active exited Update UTMP about System Boot/Shutdown
systemd-user-sessions.service loaded active exited Permit User Sessions
systemd-vconsole-setup.service loaded active exited Setup Virtual Console
tuned.service loaded active running Dynamic System Tuning Daemon
vgauthd.service loaded active running VGAuth Service for open-vm-tools
vmtoolsd.service loaded active running Service for virtual machines hosted on VMware
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.
39 loaded units listed. Pass --all to see loaded but inactive units, too.
To show all installed unit files use 'systemctl list-unit-files'.