使用systemctl进行Linux管理资源管理

systemctl 是用于控制systemd的实用程序。systemctl为CentOS管理员提供了在systemd上执行多种操作的能力，包括

  • 配置systemd单位
  • 获取systemd untis的状态
  • 开始和停止服务
  • 为运行时启用/禁用systemd服务等。

systemctl 的命令语法很基本，但可以与开关和选项纠缠在一起。我们将介绍管理CentOS Linux所需的 systemctl 最重要的功能。

Basic systemctl syntax:
systemctl [OPTIONS] COMMAND [NAME]

以下是 systemctl 使用的常用命令-

  • start
  • stop
  • restart
  • reload
  • status
  • is-active
  • list-units
  • enable
  • disable
  • cat
  • show

我们已经讨论过 启动 ， 停止 ， 重新加载 ， 重新启动 ， 启用 和 禁用 systemctl。 我们来看看其余常用的命令。

状态

以最简单的形式，状态命令可用于查看整个系统的状态 -

[root@localhost rdc]# systemctl status
 ● localhost.localdomain
  State: running
  Jobs: 0 queued
  Failed: 0 units
  Since: Thu 2017-01-19 19:14:37 EST; 4h 5min ago
CGroup: /
       ├─1 /usr/lib/systemd/systemd --switched-root --system --deserialize 21
       ├─user.slice
       │ └─user-1002.slice
       │   └─session-1.scope
       │     ├─2869 gdm-session-worker [pam/gdm-password]
       │     ├─2881 /usr/bin/gnome-keyring-daemon --daemonize --login
       │     ├─2888 gnome-session --session gnome-classic
       │     ├─2895 dbus-launch --sh-syntax --exit-with-session

上面的输出已经被浓缩了。在现实世界中， systemctl状态 将输出约100行treed进程状态。

假设我们想检查我们的防火墙服务的状态 -

[root@localhost rdc]# systemctl status firewalld
● firewalld.service - firewalld - dynamic firewall daemon
Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled; vendor preset: enabled)
Active: active (running) since Thu 2017-01-19 19:14:55 EST; 4h 12min ago
 Docs: man:firewalld(1)
Main PID: 825 (firewalld)
CGroup: /system.slice/firewalld.service
       └─825 /usr/bin/python -Es /usr/sbin/firewalld --nofork --nopid

如您所见，我们的防火墙服务目前处于活动状态，并且已经运行了4个多小时。

list-units

list-units命令允许我们列出某种类型的所有单位。让我们来检查由 systemd 管理的套接字-

[root@localhost]# systemctl list-units --type=socket
UNIT                         LOAD     ACTIVE     SUB     DESCRIPTION     
avahi-daemon.socket          loaded   active  running    Avahi mDNS/DNS-SD Stack Activation Socket
cups.socket                  loaded   active  running    CUPS Printing Service Sockets
dbus.socket                  loaded   active  running    D-Bus System Message Bus Socket
dm-event.socket              loaded   active  listening  Device-mapper event daemon FIFOs
iscsid.socket                loaded   active  listening  Open-iSCSI iscsid Socket
iscsiuio.socket              loaded   active  listening  Open-iSCSI iscsiuio Socket
lvm2-lvmetad.socket          loaded   active  running    LVM2 metadata daemon socket
lvm2-lvmpolld.socket         loaded   active  listening  LVM2 poll daemon socket
rpcbind.socket               loaded   active  listening  RPCbind Server Activation Socket
systemd-initctl.socket       loaded   active  listening  /dev/initctl Compatibility Named Pipe
systemd-journald.socket      loaded   active  running    Journal Socket
systemd-shutdownd.socket     loaded   active  listening  Delayed Shutdown Socket
systemd-udevd-control.socket loaded   active  running    udev Control Socket
systemd-udevd-kernel.socket  loaded   active  running    udev Kernel Socket
virtlockd.socket             loaded   active  listening  Virtual machine lock manager socket
virtlogd.socket              loaded   active  listening  Virtual machine log manager socket

现在我们来检查当前正在运行的服务 -

[root@localhost rdc]# systemctl list-units --type=service
UNIT                      LOAD     ACTIVE     SUB     DESCRIPTION
abrt-ccpp.service         loaded   active   exited    Install ABRT coredump hook
abrt-oops.service         loaded   active   running   ABRT kernel log watcher
abrt-xorg.service         loaded   active   running   ABRT Xorg log watcher
abrtd.service             loaded   active   running   ABRT Automated Bug Reporting Tool
accounts-daemon.service   loaded   active   running   Accounts Service
alsa-state.service        loaded   active   running   Manage Sound Card State (restore and store)
atd.service               loaded   active   running   Job spooling tools
auditd.service            loaded   active   running   Security Auditing Service

is-active

is-active 命令是被设计为返回一个单元的状态信息的命令systemctl的一个例子。

[root@localhost rdc]# systemctl is-active ksm.service
active

cat

cat 是很少使用的命令之一。不要在shell中使用cat并输入单元文件的路径，只需使用 systemctl cat 。

[root@localhost]# systemctl cat firewalld
# /usr/lib/systemd/system/firewalld.service
[Unit]
Description=firewalld - dynamic firewall daemon
Before=network.target
Before=libvirtd.service
Before = NetworkManager.service
After=dbus.service
After=polkit.service
Conflicts=iptables.service ip6tables.service ebtables.service ipset.service
Documentation=man:firewalld(1)

[Service]
EnvironmentFile = -/etc/sysconfig/firewalld
ExecStart = /usr/sbin/firewalld --nofork --nopid $FIREWALLD_ARGS
ExecReload = /bin/kill -HUP $MAINPID
# supress to log debug and error output also to /var/log/messages
StandardOutput = null
StandardError = null

Type = dbus
BusName = org.fedoraproject.FirewallD1

[Install]
WantedBy = basic.target
Alias = dbus-org.fedoraproject.FirewallD1.service

[root@localhost]#

现在我们已经更详细地探讨了 systemd 和 systemctl ，让我们用它们来管理 cgroup 或 控制组中 的资源。