Unix жүйесіндегі inetd қызметі

Unix daemon

inetd (internet service daemon) is a super server daemon on many Unix systems that provides Internet services. For each configured service, it listens for requests from connecting clients. Requests are served by spawning a process which runs the appropriate executable, but simple services such as echo are served by inetd itself. External executables, which are run on request, can be single or multi threaded. First appearing in 4.3BSD, it is generally located at /usr/sbin/inetd. inetd is based on the (service) activator pattern

Often called a super server, inetd listens on designated ports used by Internet services such as FTP, POP3, and telnet. When a TCP packet or UDP packet arrives with a particular destination port number, inetd launches the appropriate server program to handle the connection. For services that are not expected to run with high loads, this method uses memory more efficiently, since the specific servers run only when needed. Furthermore, in inetd's "nowait" mode of service management, no network code is required in the service specific programs, as inetd hooks the network stream directly to stdin and stdout of the spawned process. For protocols that have frequent traffic, such as HTTP and POP3, either inetd's "wait" mode of operation, or a dedicated server that intercepts the traffic directly may be preferable.

In recent years, because of the security limitations in the original design of inetd, it has been replaced by xinetd, rlinetd, ucspi tcp, and others in many systems. Distributions of Linux especially have many options and Mac OS X (beginning with Mac OS X v10.2) uses xinetd. As of version Mac OS X v10.4, Apple has merged the functionality of inetd into launchd. The services provided by inetd can be omitted entirely. This is becoming more common where machines are dedicated to a single function. For example, an HTTP server could be configured to just run httpd and have no other ports open. A dedicated firewall could have no services started. systemd supports inetd services, and expands socket activation beyond IP messaging (AF INET+6) to include AF UNIX, AF NETLINK and more.

While the inetd concept as a service dispatcher is not inherently insecure, the long list of services that inetd traditionally provided gave computer security experts pause. The possibility of a service having an exploitable flaw, or the service just being abused, had to be considered. Unnecessary services being disabled and "off by default" became the mantra. It is not uncommon to find an /etc/inetd. conf with almost all the services commented out in a modern Unix distribution.