Linux xinetd (Extended Internet Services) Super Server daemon

The Linux xinetd (Extended Internet Services) daemon, also known as the super server, controls many network services.

The xinetd service listens on all ports used by the daemons it controls. When a connection is requested, xinetd determines if the client is allowed access. If the client is allowed access, xinetd starts up the desired service and allows the client to connect.

The xinetd service listens for connection requests for all of the active servers with scripts in the /etc/xinetd.d directory. There's a generic configuration file for xinetd services, /etc/xinetd.conf. The scripts in the /etc/xinetd.d directory function as service-specific configuration files.

The xinetd rpm package should be installed to to use the xinetd super server.
The following command will install the xinetd super server.

[root@RHEL03 Server]# rpm -ivh xinetd-2.3.14-10.el5.i386.rpm
warning: xinetd-2.3.14-10.el5.i386.rpm: Header V3 DSA signature: NOKEY, key ID 37017186
Preparing... ########################################### [100%]
1:xinetd ########################################### [100%]

To install telnet server, you should install the telnet-server rpm package after the installation of xinetd rpm package. The telnet-server rpm package can be installed by running the following command.

[root@RHEL03 Server]# rpm -ivh telnet-server-0.17-38.el5.i386.rpm
warning: telnet-server-0.17-38.el5.i386.rpm: Header V3 DSA signature: NOKEY, key ID 37017186
Preparing... ########################################### [100%]
1:telnet-server ########################################### [100%]

xinetd Configuration files in /etc/xinetd.d folder

The files in the /etc/xinetd.d directory specify a particular service you want to allow xinetd to manage.

The following configuration (/etc/xinetd.d/telnet) file is related to the telnet server we have just installed.

# default: on
# description: The telnet server serves telnet sessions; it uses \
# unencrypted username/password pairs for authentication.
service telnet
{
flags = REUSE
socket_type = stream
wait = no
user = root
server = /usr/sbin/in.telnetd
log_on_failure += USERID
disable = yes
}

The following table is the description of different parameters used in xinetd file. Note that the "disable" parameter is set to yes, which disables the telnet server. If you want to enable the telnet server, this value should be "no".

Parameter	Description
flags	Supports different parameters for the service; REUSE is a default that supports continuous use of the service.
Options	include IPv6 to set this as a service for those types of networks.
socket_type	Specifies the communication stream.
wait	Set to yes for single-threaded applications or no for multithreaded applications.
User	Account under which the server should run.
Group	Group under which the server should run.
server	The server program.
only_from	Host name or IP address allowed to use the server.
no_access	Host name or IP address not allowed to use the server.
log_on_failure	Whether a failure should be logged
disable	By default, set to yes, which disables the service.