1. Services (daemons) can be mainly divided into stand alone (services can be started separately) and super daemons (services managed by xinetd)
2. Since super daemon is managed by a unified xinetd, it can have similar firewall management functions. In addition, the management link mechanism can be divided into multi-threaded and single-threaded (multi-threaded, single-threaded)
3. The process that starts the daemon usually adds a d at the end, such as sshd, vsftpd, httpd, etc.
4. The script started by the stand alone daemon is placed in the directory /etc/init.d, the configuration file of the super daemon is placed in /etc/xinetd.d/*, and the startup method is /etc/init.d/ xientd restart
5. The method of starting the stand alone daemon immediately can also use the service command,
6. The configuration file of the super daemon is /etc/xinetd.conf, and the individual daemon configuration files are in /etc/xinetd.d/*. In the configuration file, you can also set whether the connection to the client is connected or not, which has a similar function as a firewall.
7. If you want to manage the firewall function in a unified way, you can use /etc/hosts.{allow, deny}. If you install TCP Wrappers, you can also use additional spawn functions, etc.
8. If you want to set a service to start at boot time, you can use chkconfig, ntsysv and other commands
9. Some unnecessary services can be turned off