Inetd (Internet daemon) is a legacy service that listen for network connections for some other daemon. For example, inetd may listen for DNS connections on port 53 for the DNS daemon.
Inetd is no longer found is most modern distributions, and has mostly been replaced with xinetd (extended Internet daemon).
The inetd configuration file is located at /etc/inetd.conf. Files in the /etc/inted.d/ directory also control the behavior of inetd. Let's consider this example line in the /etc/inted.conf file.
dns stream tcp nowait root /usr/sbin/tcpd /usr/sbin/in.bind -l
- Field 1 = The name of the service as it appears in the /etc/services file (dns in this example)
- Field 2 = Socket type (stream, dgram, raw). Stream is typically used when protocol is TCP, and dgram is typically used when protocol is UDP.
- Field 3 = Protocol (TCP or UDP)
- Field 4 = Nowait will be used if field 2 is stream or raw. Wait or nowait cam be used if field 2 is dgram.
- Field 5 = User account use, such as root, nobody, or user1.
- Field 6 = If /usr/sbin/tcpd is listed, the service is using TCP wrapper for security (more below). Otherwise, the path to the service daemon will probably be listed, such as /usr/bin/bind.
- Field 7 = Parameters (optional)
When field 6 of the /etc/inetd.conf file is /usr/sbin/tcpd, the TCP deamon is being used. If tcpd is being used, when a remote client submits a request to the server for a service, the /etc/hosts.allow and /etc/hosts.deny files will be checked to determine if the client is allowed or denied access to the deamon. If allowed, the TCP deamon calls the server program into action.