Inetd

inetd, short for Internet daemon, is a super-server daemon used on many Unix-like systems to manage Internet services. It listens on multiple network ports and starts the appropriate service on demand when a connection arrives, allowing each service to run as a separate process only when needed. By centralizing port management, inetd reduces the number of idle daemons and simplifies configuration.

Operation and configuration: inetd reads entries from a configuration file (commonly /etc/inetd.conf). Each entry specifies the service name, socket type (stream or datagram), protocol (tcp or udp), wait/nowait behavior, user and group to run the server as, and the server program along with its arguments. Example: telnet stream tcp nowait root /usr/sbin/in.telnetd in.telnetd. When a connection or datagram arrives, inetd starts the designated server and connects the client socket to the server’s standard input/output. The wait/nowait flag controls whether inetd handles multiple simultaneous connections for that service.

Security and modules: inetd is commonly used with TCP wrappers via tcpd to provide access control; logs typically go to syslog. The model minimizes resource usage but shifts responsibility for security to the individual services and wrappers.

History and status: Inetd originated in BSD Unix and became standard on many systems; various Linux distributions provided inetd or xinetd. In modern systems, inetd is often superseded by xinetd or by systemd’s socket activation, though some systems retain inetd for compatibility. Xinetd adds finer-grained access control and logging; systemd can provide similar on-demand activation via socket units.