Cognitive system services

1. What is a system service
service ：service Provide some functions , Such as power management, Internet service, scheduled tasks, etc .
Realization service Your program becomes daemon.
In general daemon Is equal to service.
daemon Main categories of ：
stand_alone Self initiated Services Fast response
super_daemon Through unified xinetd management .
View the corresponding relationship between the service and the port number ：cat /etc/service
daemon The startup method and startup script
Starting mode ： Using scripts directly
/etc/init.d/* Place the startup script
/etc/sysconfig/* The configuration file
/etc/xinetd.config, /etc/xinetd.d/* super daemon The configuration file
Check the startup status, such as ： /etc/init.d/syslog satus
Start as :/etc/init.d/syslog restart
Firewall Management ： File joining ip etc/hosts.allow etc/hosts.deny