系统控制是一个系统负责控制的实用程序系统系统和服务经理。系统是系统管理守护进程、实用程序和库的集合，可替代系统V初始化守护进程。 Systemd 充当类 UNIX 系统的中央管理和配置平台。
在 Linux 生态系统中系统除了少数例外，大多数标准 Linux 发行版都已实现。 Systemd 通常但并非总是所有其他守护进程的父进程。
本文旨在阐明“如何控制系统和服务在运行 systemd 的系统上。
从 Systemtd 和 Systemctl 基础知识开始
1.首先，检查是否系统您的系统上是否安装了，当前安装的 Systemd 版本是什么？
# systemctl --version systemd 215 +PAM +AUDIT +SELINUX +IMA +SYSVINIT +LIBCRYPTSETUP +GCRYPT +ACL +XZ -SECCOMP -APPARMOR
从上面的例子可以清楚地看出，我们有systemd215版本已安装。
2.检查二进制文件和库的位置系统和系统控制已安装。
# whereis systemd systemd: /usr/lib/systemd /etc/systemd /usr/share/systemd /usr/share/man/man1/systemd.1.gz # whereis systemctl systemctl: /usr/bin/systemctl /usr/share/man/man1/systemctl.1.gz
3.检查是否系统是否正在运行。
# 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 正在作为父守护进程运行（PID=1）。在上面的命令中附注和 （-e) 选择所有进程，(-一个) 选择除会话领导者之外的所有进程并且 (-f）用于完整格式列表（即-eaf）。
另请注意上例中的方括号以及后续示例中的其余部分。方括号表达式是 grep 字符类模式匹配的一部分。
4.分析systemd启动过程。
# systemd-analyze Startup finished in 487ms (kernel) + 2.776s (initrd) + 20.229s (userspace) = 23.493s
5.分析启动时每个进程所花费的时间。
# systemd-analyze blame 8.565s mariadb.service 7.991s webmin.service 6.095s postfix.service 4.311s httpd.service 3.926s firewalld.service 3.780s kdump.service 3.238s tuned.service 1.712s network.service 1.394s lvm2-monitor.service 1.126s systemd-logind.service ....
6.分析启动时的关键链。
# systemd-analyze critical-chain
The time after the unit is active or started is printed after the "@" character.
The time the unit takes to start is printed after the "+" character.
multi-user.target @20.222s
└─mariadb.service @11.657s +8.565s
└─network.target @11.168s
└─network.service @9.456s +1.712s
└─NetworkManager.service @8.858s +596ms
└─firewalld.service @4.931s +3.926s
└─basic.target @4.916s
└─sockets.target @4.916s
└─dbus.socket @4.916s
└─sysinit.target @4.905s
└─systemd-update-utmp.service @4.864s +39ms
└─auditd.service @4.563s +301ms
└─systemd-tmpfiles-setup.service @4.485s +69ms
└─rhel-import-state.service @4.342s +142ms
└─local-fs.target @4.324s
└─boot.mount @4.286s +31ms
└─systemd-fsck@dev-disk-by\x2duuid-79f594ad\x2da332\x2d4730\x2dbb5f\x2d85d19608096
└─dev-disk-by\x2duuid-79f594ad\x2da332\x2d4730\x2dbb5f\x2d85d196080964.device @4
重要的: Systemctl 接受服务 (。服务), 挂载点 (。山), 插座 (。插座）和设备（。设备) 为单位。
7.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 .....
8.列出所有正在运行的单元。
# systemctl list-units UNIT LOAD ACTIVE SUB DESCRIPTION proc-sys-fs-binfmt_misc.automount loaded active waiting Arbitrary Executable File Formats File Syste sys-devices-pc...0-1:0:0:0-block-sr0.device loaded active plugged VBOX_CD-ROM sys-devices-pc...:00:03.0-net-enp0s3.device loaded active plugged PRO/1000 MT Desktop Adapter sys-devices-pc...00:05.0-sound-card0.device loaded active plugged 82801AA AC'97 Audio Controller sys-devices-pc...:0:0-block-sda-sda1.device loaded active plugged VBOX_HARDDISK sys-devices-pc...:0:0-block-sda-sda2.device loaded active plugged LVM PV Qzyo3l-qYaL-uRUa-Cjuk-pljo-qKtX-VgBQ8 sys-devices-pc...0-2:0:0:0-block-sda.device loaded active plugged VBOX_HARDDISK sys-devices-pl...erial8250-tty-ttyS0.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS0 sys-devices-pl...erial8250-tty-ttyS1.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS1 sys-devices-pl...erial8250-tty-ttyS2.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS2 sys-devices-pl...erial8250-tty-ttyS3.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS3 sys-devices-virtual-block-dm\x2d0.device loaded active plugged /sys/devices/virtual/block/dm-0 sys-devices-virtual-block-dm\x2d1.device loaded active plugged /sys/devices/virtual/block/dm-1 sys-module-configfs.device loaded active plugged /sys/module/configfs ...
9.列出所有失败的单位。
# systemctl --failed UNIT LOAD ACTIVE SUB DESCRIPTION kdump.service loaded failed failed Crash recovery kernel arming 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. 1 loaded units listed. Pass --all to see loaded but inactive units, too. To show all installed unit files use 'systemctl list-unit-files'.
10.检查是否有一个单位（cron.service) 是否启用？
# systemctl is-enabled crond.service enabled
11.检查某个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 2015-04-28 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.
使用 Systemctl 控制和管理服务
12.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
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
....
13.如何启动、重新启动、停止、重新加载和检查服务的状态（httpd.服务）在Linux中。
# 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 2015-04-28 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.
笔记：当我们使用像这样的命令时开始,重新启动,停止和重新加载使用 systemctl，我们不会在终端上得到任何输出，唯一的输出地位命令将打印输出。
14.如何激活服务并在启动时启用或禁用服务（系统启动时自动启动服务）。
# systemctl is-active httpd.service # systemctl enable httpd.service # systemctl disable httpd.service
15.如何屏蔽（使其无法启动）或取消屏蔽服务（httpd.服务）。
# systemctl mask httpd.service ln -s '/dev/null' '/etc/systemd/system/httpd.service' # systemctl unmask httpd.service rm '/etc/systemd/system/httpd.service'
16.如何使用 systemctl 命令终止服务。
# systemctl kill httpd # systemctl status httpd httpd.service - The Apache HTTP Server Loaded: loaded (/usr/lib/systemd/system/httpd.service; enabled) Active: failed (Result: exit-code) since Tue 2015-04-28 18:01:42 IST; 28min ago Main PID: 2881 (code=exited, status=0/SUCCESS) Status: "Total requests: 0; Current requests/sec: 0; Current traffic: 0 B/sec" Apr 28 17:37:29 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled. Apr 28 17:37:29 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled. Apr 28 17:37:39 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled. Apr 28 17:37:39 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled. Apr 28 17:37:49 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled. Apr 28 17:37:49 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled. Apr 28 17:37:59 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled. Apr 28 17:37:59 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled. Apr 28 18:01:42 tecmint systemd[1]: httpd.service: control process exited, code=exited status=226 Apr 28 18:01:42 tecmint systemd[1]: Unit httpd.service entered failed state. Hint: Some lines were ellipsized, use -l to show in full.
使用 Systemctl 控制和管理挂载点
17.列出所有系统安装点。
# systemctl list-unit-files --type=mount UNIT FILE STATE 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
18。如何安装、卸载、重新安装、重新加载系统安装点以及检查系统上安装点的状态？
# systemctl start tmp.mount
# systemctl stop tmp.mount
# systemctl restart tmp.mount
# systemctl reload tmp.mount
# systemctl status tmp.mount
tmp.mount - Temporary Directory
Loaded: loaded (/usr/lib/systemd/system/tmp.mount; disabled)
Active: active (mounted) since Tue 2015-04-28 17:46:06 IST; 2min 48s ago
Where: /tmp
What: tmpfs
Docs: man:hier(7)
https://www.freedesktop.org/wiki/Software/systemd/APIFileSystems
Process: 3908 ExecMount=/bin/mount tmpfs /tmp -t tmpfs -o mode=1777,strictatime (code=exited, status=0/SUCCESS)
Apr 28 17:46:06 tecmint systemd[1]: Mounting Temporary Directory...
Apr 28 17:46:06 tecmint systemd[1]: tmp.mount: Directory /tmp to mount over is not empty, mounting anyway.
Apr 28 17:46:06 tecmint systemd[1]: Mounted Temporary Directory.
19.如何在启动时激活、启用或禁用挂载点（系统启动时自动挂载）。
# systemctl is-active tmp.mount # systemctl enable tmp.mount # systemctl disable tmp.mount
20.如何在 Linux 中屏蔽（使其无法启动）或取消屏蔽挂载点。
# systemctl mask tmp.mount ln -s '/dev/null' '/etc/systemd/system/tmp.mount' # systemctl unmask tmp.mount rm '/etc/systemd/system/tmp.mount'
使用 Systemctl 控制和管理套接字
21.列出所有可用的系统套接字。
# systemctl list-unit-files --type=socket UNIT FILE STATE dbus.socket static dm-event.socket enabled lvm2-lvmetad.socket enabled rsyncd.socket disabled sshd.socket disabled syslog.socket static systemd-initctl.socket static systemd-journald.socket static systemd-shutdownd.socket static systemd-udevd-control.socket static systemd-udevd-kernel.socket static 11 unit files listed.
22.如何启动、重新启动、停止、重新加载和检查套接字的状态（示例：杯子.插座）在Linux中。
# systemctl start cups.socket # systemctl restart cups.socket # systemctl stop cups.socket # systemctl reload cups.socket # systemctl status cups.socket cups.socket - CUPS Printing Service Sockets Loaded: loaded (/usr/lib/systemd/system/cups.socket; enabled) Active: active (listening) since Tue 2015-04-28 18:10:59 IST; 8s ago Listen: /var/run/cups/cups.sock (Stream) Apr 28 18:10:59 tecmint systemd[1]: Starting CUPS Printing Service Sockets. Apr 28 18:10:59 tecmint systemd[1]: Listening on CUPS Printing Service Sockets.
23.如何激活套接字并在启动时启用或禁用（系统启动时自动启动套接字）。
# systemctl is-active cups.socket # systemctl enable cups.socket # systemctl disable cups.socket
24.如何屏蔽（使其无法启动）或取消屏蔽套接字 (cups.socket)。
# systemctl mask cups.socket ln -s '/dev/null' '/etc/systemd/system/cups.socket' # systemctl unmask cups.socket rm '/etc/systemd/system/cups.socket'
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