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使用 systemctl 进行资源管理

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 单元
  • 获取 systemd 单元的状态
  • 启动和停止服务
  • 启用/禁用 systemd 运行时服务等。

systemctl 的命令语法非常简单，但可能会与开关和选项纠缠在一起。我们将介绍管理 CentOS Linux 所需的 systemctl 的最基本功能。

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

我们已经讨论了 systemctl 的 start、stop、reload、restart、enable 和 disable。让我们来回顾一下其余常用的命令。

status

status 命令最简单的形式可用于查看整个系统状态 −

[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

以上输出已压缩。在实际情况下，systemctl status 将输出大约 100 行树状进程状态。

假设我们要检查 firewalld 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 firewall 防火墙服务目前处于活动状态，并且已持续 4 个小时以上。

list-units

list-units 命令允许我们列出特定类型的所有单元。让我们检查由 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

现在让我们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 systemctl 命令的一个示例，旨在返回单元的状态信息。

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

cat

cat 是很少使用的命令之一。无需在 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]#

现在我们已经详细了解了 systemd 和 systemctl，让我们使用它们来管理 cgroups 或 控制组 中的资源。

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