[Linux] system services and daemon

Linux system services run on daemon. They are mainly divided into two categories:

1) standalone: You can start services independently, such as httpd and vsftpd. It features fast response, but high resource usage.

2) super daemon: A special unified management of daemon. When the client does not have a request, the services are not started until a request is sent from the client.

Daemon STARTUP script and startup Method

1)/etc/init. d/*: place the Startup Script

2)/etc/sysconfig/*: Service initialization environment configuration file

3)/etc/xinetd. conf and/etc/xinetd. d/*: configuration file of super daemon

4)/etc/*: service configuration file

5)/var/lib/*: database generated by the Service

6)/var/run/*: Service PID

Standalone startup and shutdown Methods

First, put the standalone STARTUP script in the/etc/init. d/directory, and then use the script to start and close the service:

# /etc/init.d/syslogUsage: /etc/init.d/syslog {start|stop|status|restart|condrestart}

You can also use the service command (the effect is the same as that of/etc/init. d ):

service [service name] (start|stop|restart|status|...)service --status-all

How to enable or disable super daemon
Super daemon itself is a standalone service, as shown below:

# /etc/init.d/xinetd statusxinetd (pid  3543) is running...

The service managed by it is super daemon, and their configuration files are stored in/etc/xinetd. d /*

The following is an example:

First, edit the/etc/xinetd. d/rsync file and set disable = no to start the super daemon

Restart the xinetd service:

# /etc/init.d/xinetd restartStopping xinetd: [  OK  ]Starting xinetd: [  OK  ]

Then, you can see that the service has been started:

# cat /etc/services |grep rsyncrsync           873/tcp                         # rsyncrsync           873/udp                         # rsync

Chkconfig-set startup daemon

Chkconfig -- list [service name] -- View chkconfig [-- level [0123456] [service name] [on | off] # view httpd configuration # chkconfig -- list httpdhttpd 0: off 1: off 2: on 3: on 4: on 5: on 6: off # Check which services are automatically started in level 3 # chkconfig -- list | grep '3: on 'crond 0: off 1: off 2: on 3: on 4: on 5: on 6: offhttpd 0: off 1: off 2: on 3: on 4: on 5: on 6: offirqbalance 0: off 1: off 2: on 3: on 4: on 5: on 6: offmicrocode_ctl 0: off 1: off 2: on 3: on 4: on 5: on 6: offmysqld 0: off 1: off 2: on 3: on 4: on 5: on 6: offnetwork 0: off 1: off 2: on 3: on 4: on 5: on 6: offsshd 0: off 1: off 2: on 3: on 4: on 5: on 6: offsyslog 0: off 1: off 2: on 3: on 4: on 5: on 6: offxinetd 0: off 1: off 2: off 3: on 4: on 5: on 6: off # configure httpd to automatically start when the level is 345 # chkconfig -- level 345 httpd on

In addition to setting system services, chkconfig can also add its own services, such:

#vi /etc/init.d/myservice#!/bin/bash# chkconfig: 35 80 70......chkconfig --add myservicechkconfig --del myservice

Netstat-view network services enabled by the System

Netstat-tulp -- find out which network services are currently enabled by the system netstat-lnp -- find all the services with monitoring (including socket status)

References: http://www.cnblogs.com/ggjucheng/archive/2012/01/08/2316661.html