Linux控制服务和守护进程

控制服务和守护进程

1.systemd

1.1.systemd简介

systemd是用户空间的第一个应用程序,即 /sbin/init

init程序的类型

SysV风格:init(centos5),实现系统初始化时,随后的初始化操作都是借助于脚本来实现

特点:

脚本中含有大量的命令,每个命令都要启动一个进程,命令执行完以后就要终止这个进程。如此一来,系统初始化时将大量的创建进程,销毁进程,工作效率会非常低。

服务间可能会存在依赖关系,必须严格按照一定的顺序来启动服务,前一个服务没启动完后面的服务就无法执行启动过程。不能并行进行。

配置文件:/etc/inittab

Upstart风格:init(centos6),由ubuntu研发的,通过总线形式接近于并行的方式工作,效率比Sysv高。

特点:

基于总线方式能够让进程间互相通信的一个应用程序

不用等服务启动完成,只要一初始化就可以把自己的状态返回给其他进程

配置文件:/etc/inittab,/etc/init/*.conf

Systemd风格:systemd(centos7)

特点:启动速度比SysV和Upstar都快

不需要通过任何脚本来启动服务,systemd自身就可以启动服务,其本身就是一个强大的解释器,启动服务时不需要sh/bash的参与

systemd不真正在系统初始化时去启动任何一个服务

只要服务没有用到,它告诉你启动了,实际上并没有启动。仅当第一次去访问时才会真正启动服务

配置文件:/usr/lib/systemd/system,/etc/systemd/system

系统启动和服务器进程由systemd系统和服务管理器进行管理。此程序提供了一种方式,可以在启动时和运行中的系统上激活系统资源、服务器守护进程和其他进程。

守护进程是在执行各种任务的后台等待或运行的进程。为了倾听连接,守护进程使用套接字。套接字可以由守护进程创建,或者与守护进程分离,并且可能由另一个进程创建(如systemd),随后在客户端建立连接时将套接字传递到守护进程。

服务通常指的是一个或多个守护进程,但启动或停止一项服务可能会对系统的状态进行一次性更改(如配置网络接口),不会留下守护进程之后继续运行。

1.2.systemd的新特性

系统引导时实现服务并进行启动

按需激活进程

系统状态快照

基于依赖关系定义服务控制逻辑

1.3.systemd的核心概念Unit

systemd使用unit的概念来管理服务,这些unit表现为一个个配置文件。

systemd通过对这些配置文件进行标识和配置达到管理服务的目的:

//这些unit文件中主要包含了系统服务、监听socket、保存的系统快照
//及其它与init相关的信息保存至以下目录:
/usr/lib/systemd/system
/run/systemd/system
/etc/systemd/system

Unit的类型

Service unit    //文件扩展名为.service,用于定义系统服务
Target unit //文件扩展名为.target,用于模拟实现“运行级别”
runlevel0.target和poweroff.target //关机
runlevel1.target和rescue.target //单用户模式
runlevel2.target和multi-user.target //对于systemd来说,2/3/4级别没有区别
runlevel3.target和multi-user.target //对于systemd来说,2/3/4级别没有区别
runlevel4.target和multi-user.target //对于systemd来说,2/3/4级别没有区别
runlevel5.target和graphical.target //图形级别
runlevel6.target和reboot.target //重启
Device unit //文件扩展名为.device,用于定义内核识别的设备
Mount unit //文件扩展名为.mount,用于定义文件系统挂载点
Socket unit //文件扩展名为.socket,用于标识进程间通信用的socket文件
Snapshot unit //文件扩展名为.snapshot,用于管理系统快照
Swap unit //文件扩展名为.swap,用于标识swap设备
Automount unit //文件扩展名为.automount,用于实现文件系统的自动挂载点
Path unit //文件扩展名为.path,用于定义文件系统中的一个文件或目录

Unit关键特性

//基于socket的激活机制:
socket与服务程序分离,当有人去访问时才会真正启动服务,以此来实现按需激活进程与服务的并行启动
//基于bus的激活机制:
所有使用dbus实现进程间通信的服务,可以在第一次被访问时按需激活
//基于device的激活机制:
支持基于device激活的系统服务,可以在特定类型的硬件接入到系统中时,按需激活其所需要用到的服务
//基于path的激活机制:
某个文件路径变得可用,或里面出现新文件时就激活某服务
//系统快照:
保存各unit的当前状态信息于持久存储设备中,必要时能自动载入
//向后兼容sysv init脚本

不兼容特性

//systemctl命令固定不变
//非由systemd启动的服务,systemctl无法与之通信
//只有已经启动的服务在级别切换时才会执行stop,在centos6以前是所有S开头的服务全部start,所有K开头的服务全部stop
//系统服务不会读取任何来自标准输入的数据流
//每个服务的unit操作均受5分钟超时时间限制

2.使用systemctl管理服务

//语法:systemctl COMMAND name[.service|.target]
//常用COMMAND:
start name.service //启动服务
stop name.service //停止服务
restart name.service //重启服务
status name.service //查看服务状态
[root@localhost ~]# systemctl stop postfix.service
[root@localhost ~]# systemctl status postfix.service
● postfix.service - Postfix Mail Transport Agent
Loaded: loaded (/usr/lib/systemd/system/postfix.service; enabled; vendor preset: disabled)
Active: inactive (dead) since 三 2019-09-25 15:11:46 CST; 23s ago
Process: 2146 ExecStop=/usr/sbin/postfix stop (code=exited, status=0/SUCCESS)
Process: 1177 ExecStart=/usr/sbin/postfix start (code=exited, status=0/SUCCESS)
Process: 1165 ExecStartPre=/usr/libexec/postfix/chroot-update (code=exited, status=0/SUCCESS)
Process: 1097 ExecStartPre=/usr/libexec/postfix/aliasesdb (code=exited, status=0/SUCCESS)
Main PID: 1321 (code=killed, signal=TERM) 9月 25 10:06:41 localhost.localdomain systemd[1]: Starting Postfix Mail Transport Agent...
9月 25 10:06:43 localhost.localdomain postfix/postfix-script[1319]: starting the Postfix mail system
9月 25 10:06:43 localhost.localdomain postfix/master[1321]: daemon started -- version 2.10.1, configuration ...fix
9月 25 10:06:43 localhost.localdomain systemd[1]: Started Postfix Mail Transport Agent.
9月 25 15:11:46 localhost.localdomain systemd[1]: Stopping Postfix Mail Transport Agent...
9月 25 15:11:46 localhost.localdomain systemd[1]: Stopped Postfix Mail Transport Agent.
Hint: Some lines were ellipsized, use -l to show in full.
[root@localhost ~]# systemctl start postfix.service
[root@localhost ~]# systemctl status postfix.service
● postfix.service - Postfix Mail Transport Agent
Loaded: loaded (/usr/lib/systemd/system/postfix.service; enabled; vendor preset: disabled)
Active: active (running) since 三 2019-09-25 15:12:51 CST; 9s ago
Process: 2146 ExecStop=/usr/sbin/postfix stop (code=exited, status=0/SUCCESS)
Process: 2168 ExecStart=/usr/sbin/postfix start (code=exited, status=0/SUCCESS)
Process: 2165 ExecStartPre=/usr/libexec/postfix/chroot-update (code=exited, status=0/SUCCESS)
Process: 2163 ExecStartPre=/usr/libexec/postfix/aliasesdb (code=exited, status=0/SUCCESS)
Main PID: 2240 (master)
CGroup: /system.slice/postfix.service
├─2240 /usr/libexec/postfix/master -w
├─2241 pickup -l -t unix -u
└─2242 qmgr -l -t unix -u 9月 25 15:12:51 localhost.localdomain systemd[1]: Starting Postfix Mail Transport Agent...
9月 25 15:12:51 localhost.localdomain postfix/master[2240]: daemon started -- version 2.10.1, configuration ...fix
9月 25 15:12:51 localhost.localdomain systemd[1]: Started Postfix Mail Transport Agent.
Hint: Some lines were ellipsized, use -l to show in full.
[root@localhost ~]# systemctl restart postfix.service
[root@localhost ~]# systemctl status postfix.service
● postfix.service - Postfix Mail Transport Agent
Loaded: loaded (/usr/lib/systemd/system/postfix.service; enabled; vendor preset: disabled)
Active: active (running) since 三 2019-09-25 15:14:20 CST; 16s ago
Process: 2250 ExecStop=/usr/sbin/postfix stop (code=exited, status=0/SUCCESS)
Process: 2264 ExecStart=/usr/sbin/postfix start (code=exited, status=0/SUCCESS)
Process: 2262 ExecStartPre=/usr/libexec/postfix/chroot-update (code=exited, status=0/SUCCESS)
Process: 2259 ExecStartPre=/usr/libexec/postfix/aliasesdb (code=exited, status=0/SUCCESS)
Main PID: 2336 (master)
CGroup: /system.slice/postfix.service
├─2336 /usr/libexec/postfix/master -w
├─2337 pickup -l -t unix -u
└─2338 qmgr -l -t unix -u 9月 25 15:14:20 localhost.localdomain systemd[1]: Starting Postfix Mail Transport Agent...
9月 25 15:14:20 localhost.localdomain postfix/master[2336]: daemon started -- version 2.10.1, configuration ...fix
9月 25 15:14:20 localhost.localdomain systemd[1]: Started Postfix Mail Transport Agent.
Hint: Some lines were ellipsized, use -l to show in full.
 try-restart name.service            //条件式重启服务,若服务已经启动则重启,若服务未启动则不做任何操作
[root@localhost ~]# systemctl stop postfix.service
[root@localhost ~]# systemctl try-restart postfix.service
[root@localhost ~]# systemctl status postfix.service
● postfix.service - Postfix Mail Transport Agent
Loaded: loaded (/usr/lib/systemd/system/postfix.service; enabled; vendor preset: disabled)
Active: inactive (dead) since 三 2019-09-25 15:17:46 CST; 42s ago
Process: 2346 ExecStop=/usr/sbin/postfix stop (code=exited, status=0/SUCCESS)
Process: 2264 ExecStart=/usr/sbin/postfix start (code=exited, status=0/SUCCESS)
Process: 2262 ExecStartPre=/usr/libexec/postfix/chroot-update (code=exited, status=0/SUCCESS)
Process: 2259 ExecStartPre=/usr/libexec/postfix/aliasesdb (code=exited, status=0/SUCCESS)
Main PID: 2336 (code=killed, signal=TERM) 9月 25 15:14:20 localhost.localdomain systemd[1]: Starting Postfix Mail Transport Agent...
9月 25 15:14:20 localhost.localdomain postfix/master[2336]: daemon started -- version 2.10.1, configuration ...fix
9月 25 15:14:20 localhost.localdomain systemd[1]: Started Postfix Mail Transport Agent.
9月 25 15:17:46 localhost.localdomain systemd[1]: Stopping Postfix Mail Transport Agent...
9月 25 15:17:46 localhost.localdomain systemd[1]: Stopped Postfix Mail Transport Agent.
Hint: Some lines were ellipsized, use -l to show in full.
reload-or-restart name.service      //重载或重启服务,能reload则reload,否则restart
reload-or-try-restart name.service //重载或条件式重启服务,能reload则reload,否则try-restart
mask name.service //禁止设定为开机自启
unmask name.service //取消禁止设定为开机自启
[root@localhost ~]# systemctl mask postfix.service
Created symlink from /etc/systemd/system/postfix.service to /dev/null.
[root@localhost ~]# systemctl status postfix.service
● postfix.service
Loaded: masked (/dev/null; bad)
Active: inactive (dead) since 三 2019-09-25 15:17:46 CST; 3min 11s ago
Main PID: 2336 (code=killed, signal=TERM) 9月 25 15:14:20 localhost.localdomain systemd[1]: Starting Postfix Mail Transport Agent...
9月 25 15:14:20 localhost.localdomain postfix/master[2336]: daemon started -- version 2.10.1, configuration ...fix
9月 25 15:14:20 localhost.localdomain systemd[1]: Started Postfix Mail Transport Agent.
9月 25 15:17:46 localhost.localdomain systemd[1]: Stopping Postfix Mail Transport Agent...
9月 25 15:17:46 localhost.localdomain systemd[1]: Stopped Postfix Mail Transport Agent.
Hint: Some lines were ellipsized, use -l to show in full.
[root@localhost ~]# systemctl unmask postfix.service
Removed symlink /etc/systemd/system/postfix.service.
[root@localhost ~]# systemctl status postfix.service
● postfix.service - Postfix Mail Transport Agent
Loaded: loaded (/usr/lib/systemd/system/postfix.service; enabled; vendor preset: disabled)
Active: inactive (dead) since 三 2019-09-25 15:17:46 CST; 3min 27s ago
Main PID: 2336 (code=killed, signal=TERM) 9月 25 15:14:20 localhost.localdomain systemd[1]: Starting Postfix Mail Transport Agent...
9月 25 15:14:20 localhost.localdomain postfix/master[2336]: daemon started -- version 2.10.1, configuration ...fix
9月 25 15:14:20 localhost.localdomain systemd[1]: Started Postfix Mail Transport Agent.
9月 25 15:17:46 localhost.localdomain systemd[1]: Stopping Postfix Mail Transport Agent...
9月 25 15:17:46 localhost.localdomain systemd[1]: Stopped Postfix Mail Transport Agent.
Hint: Some lines were ellipsized, use -l to show in full.
list-dependencies name.service      //查看服务的依赖关系
is-active name.service //查看某服务当前激活与否的状态
is-enable name.service //查看服务是否开机自动启动
[root@localhost ~]# systemctl list-dependencies postfix.service
postfix.service
● ├─system.slice
● └─basic.target
● ├─microcode.service
● ├─rhel-autorelabel-mark.service
● ├─rhel-autorelabel.service
● ├─rhel-configure.service
● ├─rhel-dmesg.service
● ├─rhel-loadmodules.service
● ├─selinux-policy-migrate-local-changes@targeted.service
● ├─paths.target
● ├─slices.target
● │ ├─-.slice
● │ └─system.slice
● ├─sockets.target
● │ ├─dbus.socket
● │ ├─dm-event.socket
● │ ├─systemd-initctl.socket
● │ ├─systemd-journald.socket
● │ ├─systemd-shutdownd.socket
● │ ├─systemd-udevd-control.socket
● │ └─systemd-udevd-kernel.socket
● ├─sysinit.target
● │ ├─dev-hugepages.mount
● │ ├─dev-mqueue.mount
● │ ├─kmod-static-nodes.service
● │ ├─lvm2-lvmetad.socket
● │ ├─lvm2-lvmpolld.socket
● │ ├─lvm2-monitor.service
● │ ├─plymouth-read-write.service
lines 2-30
[root@localhost ~]# systemctl is-active postfix.service
active
[root@localhost ~]# systemctl status postfix.service
● postfix.service - Postfix Mail Transport Agent
Loaded: loaded (/usr/lib/systemd/system/postfix.service; enabled; vendor preset: disabled)
Active: active (running) since 三 2019-09-25 15:22:42 CST; 4min 22s ago
Process: 2413 ExecStart=/usr/sbin/postfix start (code=exited, status=0/SUCCESS)
Process: 2411 ExecStartPre=/usr/libexec/postfix/chroot-update (code=exited, status=0/SUCCESS)
Process: 2408 ExecStartPre=/usr/libexec/postfix/aliasesdb (code=exited, status=0/SUCCESS)
Main PID: 2485 (master)
CGroup: /system.slice/postfix.service
├─2485 /usr/libexec/postfix/master -w
├─2486 pickup -l -t unix -u
└─2487 qmgr -l -t unix -u 9月 25 15:22:41 localhost.localdomain systemd[1]: Starting Postfix Mail Transport Agent...
9月 25 15:22:42 localhost.localdomain postfix/master[2485]: daemon started -- version 2.10.1, configuration ...fix
9月 25 15:22:42 localhost.localdomain systemd[1]: Started Postfix Mail Transport Agent.
Hint: Some lines were ellipsized, use -l to show in full.
enable name.service     //设定某服务开机自动启动
disable name.service //禁止服务开机自动启动
[root@localhost ~]# systemctl enable postfix.service
[root@localhost ~]# systemctl status postfix.service
● postfix.service - Postfix Mail Transport Agent
Loaded: loaded (/usr/lib/systemd/system/postfix.service; enabled; vendor preset: disabled)
Active: active (running) since 三 2019-09-25 15:22:42 CST; 8min ago
Main PID: 2485 (master)
CGroup: /system.slice/postfix.service
├─2485 /usr/libexec/postfix/master -w
├─2486 pickup -l -t unix -u
└─2487 qmgr -l -t unix -u 9月 25 15:22:41 localhost.localdomain systemd[1]: Starting Postfix Mail Transport Agent...
9月 25 15:22:42 localhost.localdomain postfix/master[2485]: daemon started -- version 2.10.1, configuration ...fix
9月 25 15:22:42 localhost.localdomain systemd[1]: Started Postfix Mail Transport Agent.
Hint: Some lines were ellipsized, use -l to show in full.
[root@localhost ~]# systemctl disable postfix.service
Removed symlink /etc/systemd/system/multi-user.target.wants/postfix.service.
[root@localhost ~]# systemctl status postfix.service
● postfix.service - Postfix Mail Transport Agent
Loaded: loaded (/usr/lib/systemd/system/postfix.service; disabled; vendor preset: disabled)
Active: active (running) since 三 2019-09-25 15:22:42 CST; 10min ago
Main PID: 2485 (master)
CGroup: /system.slice/postfix.service
├─2485 /usr/libexec/postfix/master -w
├─2486 pickup -l -t unix -u
└─2487 qmgr -l -t unix -u 9月 25 15:22:41 localhost.localdomain systemd[1]: Starting Postfix Mail Transport Agent...
9月 25 15:22:42 localhost.localdomain postfix/master[2485]: daemon started -- version 2.10.1, configuration ...fix
9月 25 15:22:42 localhost.localdomain systemd[1]: Started Postfix Mail Transport Agent.
Hint: Some lines were ellipsized, use -l to show in full.
 isolate name.target     //切换至某级别,如systemctl isolate graphical.target就是切换至图形界面
list-unit-files --type service //查看所有服务的开机自动启动状态(是否开机自启)
list-units --type service //查看所有已经激活的服务状态信息
list-units --type target //查看所有已装载的级别
list-units --type service --all //查看所有服务(已启动/已停止)的状态信息
list -units --type target --all //查看所有的级别
[root@localhost ~]# systemctl list-unit-files --type service
UNIT FILE STATE
arp-ethers.service disabled
auditd.service enabled
autovt@.service enabled
blk-availability.service disabled
brandbot.service static
chrony-dnssrv@.service static
chrony-wait.service disabled
chronyd.service enabled
console-getty.service disabled
console-shell.service disabled
container-getty@.service static
cpupower.service disabled
crond.service enabled
dbus-org.fedoraproject.FirewallD1.service enabled
dbus-org.freedesktop.hostname1.service static
dbus-org.freedesktop.import1.service static
dbus-org.freedesktop.locale1.service static
dbus-org.freedesktop.login1.service static
dbus-org.freedesktop.machine1.service static
dbus-org.freedesktop.NetworkManager.service enabled
dbus-org.freedesktop.nm-dispatcher.service enabled
dbus-org.freedesktop.timedate1.service static
dbus.service static
debug-shell.service disabled
dm-event.service disabled
dracut-cmdline.service static
dracut-initqueue.service static
dracut-mount.service static
get-default     //查看默认运行级别
set-default name.target //设置默认运行级别
[root@localhost ~]# systemctl get-default
multi-user.target
[root@localhost ~]# 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.
    rescue      //切换至紧急救援模式(大多数服务不启动,但是会加载驱动)
emergency //切换至emergency模式(驱动不会加载,系统不会初始化,服务不会启动)
halt //关机
poweroff //关机
reboot //重启
suspend //挂起系统,此时不能关机,否则无用
hibernate //创建并保存系统快照,下次系统重启时会自动载入快照
hybrid-sleep //混合睡眠,快照并挂起
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