如何在CentOS 7.x或RHEL Linux 7上使用Systemctl
在本文中，我们将学习如何使用“systemctl”命令，“systemctl”是新版本的Linux发行版中可用的新命令，该版本用于控制系统和服务，我们将探索一些可能的方式来使用Linux中的'systemctl'命令。
检查服务状态
我们可以使用此命令来验证服务的状态。以下是检查服务的命令。
# systemctl status httpd
httpd.service - The Apache HTTP Server
Loaded: loaded (/usr/lib/systemd/system/httpd.service; disabled; vendor preset: disabled)
Active: active (running) since Thu 2016-06-02 06:48:58 EDT; 27s ago
Docs: man:httpd(8)
man:apachectl(8)
Main PID: 10011 (httpd)
Status: "Total requests: 0; Current requests/sec: 0; Current traffic: 0 B/sec"
CGroup: /system.slice/httpd.service
├─10011 /usr/sbin/httpd -DFOREGROUND
├─10012 /usr/sbin/httpd -DFOREGROUND
├─10013 /usr/sbin/httpd -DFOREGROUND
├─10014 /usr/sbin/httpd -DFOREGROUND
├─10015 /usr/sbin/httpd -DFOREGROUND
└─10016 /usr/sbin/httpd -DFOREGROUND
Jun 02 06:48:57 centos-linux-1.shared systemd[1]: Starting The Apache HTTP Server...
Jun 02 06:48:58 centos-linux-1.shared systemd[1]: Started The Apache HTTP Server.展示服务
# systemctl show httpd Type=notify Restart=no NotifyAccess=main RestartUSec=100ms TimeoutStartUSec=1min 30s TimeoutStopUSec=1min 30s WatchdogUSec=0 WatchdogTimestamp=Thu 2016-06-02 06:48:58 EDT WatchdogTimestampMonotonic=2588490928 StartLimitInterval=10000000StartLimitBurst=5 StartLimitAction=none …. . . . . AssertResult=yes ConditionTimestamp=Thu 2016-06-02 06:48:57 EDT ConditionTimestampMonotonic=2587709137 AssertTimestamp=Thu 2016-06-02 06:48:57 ED AssertTimestampMonotonic=2587709138 Transient=no This will display all the status information about http (web servers services) Verifying the Services active or enabled Here we will verify that the servers are active and they are enabled at system startup To verify the services active or not we needed to run the below command # systemctl is-active httpd.service active
使服务在系统启动时或重新启动计算机后运行
# systemctl enable httpd Created symlink from /etc/systemd/system/multi-use.rtarget.wants/httpd.service to /usr/lib/systemd/system/httpd.service.
要检查服务是否已启用，请运行以下命令
# systemctl is-enabled httpd enabled
要手动启动服务或手动重新启动服务，我们可以使用以下命令
# systemctl start httpd # systemctl restart httpd
要列出依赖项，我们可以使用以下命令
# systemctl list-dependencies httpd httpd.service ├─-.mount ├─system.slice └─basic.target ├─microcode.service ├─rhel-autorelabel-mark.service ├─rhel-autorelabel. service ├─rhel-configure.service ├─rhel-dmesg.service ├─rhel-loadmodules.service ├─paths.target ├─slices.target │ ├─-.slice │ └─system.slice… … . ..
列出当前在后台运行的所有作业
# systemctl list-jobs No jobs running.
列出所有已安装的单位文件
# systemctl list-unit files
列出特定服务的所有已安装单位文件
# systemctl list-unit-files | grep httpd httpd.service enabled
列出所有已安装的套接字和这些类型
# systemctl list-sockets --show-types LISTEN TYPE UNIT ACTIVATES /dev/log Datagram systemd-journald.socket systemd-j /run/dmeventd-client FIFO dm-event.socket dm-event. /run/dmeventd-server FIFO dm-event.socket dm-event. /run/lvm/lvmetad.socket Stream lvm2-lvmetad.socket lvm2-lvme /run/lvm/lvmpolld.socket Stream lvm2-lvmpolld.socket lvm2-lvmp /run/systemd/initctl/fifo FIFO systemd-initctl.socket systemd-i /run/systemd/journal/socket Datagram systemd-journald.socket systemd-j /run/systemd/journal/stdout Stream systemd-journald.socket systemd-j /run/systemd/shutdownd Datagram systemd-shutdownd.socket systemd-s /run/udev/control SequentialPacket systemd-udevd-control.socket systemd-u /var/run/dbus/system_bus_socket Stream dbus.socket dbus.serv kobject-uevent 1 Netlink systemd-udevd-kernel.socket systemd-u 12 sockets listed. Pass --all to see loaded but inactive sockets, too.
设置/列出默认目标（平均运行级别）
# systemctl set-default multi-user.target Removed symlink /etc/systemd/system/default.target. Created symlink from /etc/systemd/system/default.target to /usr/lib/systemd/system/multi-user.target. # systemctl get-default multi-user.target
屏蔽和取消屏蔽服务
在某些情况下，尤其是在大公司中，其中一个管理员已停止服务器，其他管理员将启动服务，为避免这种情况，我们可以屏蔽和取消屏蔽服务，如果某些服务在不取消屏蔽的情况下停止，我们将无法启动服务再次
# systemctl mask httpd Created symlink from /etc/systemd/system/httpd.service to /dev/null.
屏蔽后查看服务状态
# httpd.service Loaded: masked (/dev/null) Active: active (running) since Thu 2016-06-02 07:03:27 EDT; 10min ago Main PID: 10128 (httpd) Status: "Total requests: 0; Current requests/sec: 0; Current traffic: 0 B/sec" CGroup: /system.slice/httpd.service ├─10128 /usr/sbin/httpd -DFOREGROUND ├─10129 /usr/sbin/httpd -DFOREGROUND ├─10130 /usr/sbin/httpd -DFOREGROUND ├─10131 /usr/sbin/httpd -DFOREGROUND ├─10132 /usr/sbin/httpd -DFOREGROUND └─10133 /usr/sbin/httpd -DFOREGROUND Jun 02 07:03:27 centos-linux-1.shared systemd[1]: Starting The Apache HTTP Server... Jun 02 07:03:27 centos-linux-1.shared systemd[1]: Started The Apache HTTP Server. Jun 02 07:13:47 centos-linux-1.shared systemd[1]: httpd.service: Got notification m.... Jun 02 07:13:57 centos-linux-1.shared systemd[1]: httpd.service: Got notification m.... Jun 02 07:14:07 centos-linux-1.shared systemd[1]: httpd.service: Got notification m.... Jun 02 07:14:17 centos-linux-1.shared systemd[1]: httpd.service: Got notification m.... Hint: Some lines were ellipsized, use -l to show in full.
如果我们尝试启动MaskedServices，它将显示错误
# systemctl start httpd Failed to start httpd.service: Unit httpd.service is masked.
要将服务屏蔽为启动，我们需要运行以下命令
# systemctl unmask httpd Removed symlink /etc/systemd/system/httpd.service.
取消屏蔽服务后，我们可以重新启动服务
# systemctl start httpd # systemctl status httpd httpd.service - The Apache HTTP Server Loaded: loaded (/usr/lib/systemd/system/httpd.service; disabled; vendor preset: disabled) Active: active (running) since Thu 2016-06-02 07:03:27 EDT; 18min ago Docs: man:httpd(8) man:apachectl(8) Main PID: 10128 (httpd) Status: "Total requests: 0; Current requests/sec: 0; Current traffic: 0 B/sec" CGroup: /system.slice/httpd.service ├─10128 /usr/sbin/httpd -DFOREGROUND ├─10129 /usr/sbin/httpd -DFOREGROUND ├─10130 /usr/sbin/httpd -DFOREGROUND ├─10131 /usr/sbin/httpd -DFOREGROUND ├─10132 /usr/sbin/httpd -DFOREGROUND └─10133 /usr/sbin/httpd -DFOREGROUND
我们可以在Linux机器上创建服务的快照
快照是指系统管理器的保存状态。快照仅用于保存正在运行或已停止的单元的还原。
要拍摄服务快照，我们可以使用
# systemctl snapshot httpd ht.tpdsnapshot
查看服务快照的状态
# systemctl status httpd.snapshot httpd.snapshot Loaded: loaded Active: inactive (dead) Jun 02 07:26:31 centos-linux-1.shared systemd[1]: Created snapshot httpd.snapshot.
删除快照并检查服务快照的状态
# systemctl delete httpd.snapshot # systemctl status httpd.snapshot httpd.snapshot Loaded: not-found (Reason: No such file or directory) Active: inactive (dead) Jun 02 07:26:31 centos-linux-1.shared systemd[1]: Created snapshot httpd.snapshot. Jun 02 07:29:05 centos-linux-1.shared systemd[1]: Removing snapshot httpd.snapshot.
在本文之后，我们现在可以控制新版本或最新版本的Linux中的服务，其中“systemctl”是旧版本Linux中的service命令的替换。希望这对您的工作有所帮助。