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BSD Today: inetd and inetd.conf - Managing Your System's Internet Switchboard Operator

May 09, 2000, 07:27 (0 Talkback[s])
(Other stories by Brett Glass)

[ Thanks to Jeremy Reed for this link. ]

"The file /etc/inetd.conf is vitally important to your system's security and well-being -- especially if your system has a 24x7 connection to the Internet. Many common security holes in UNIX systems (and UNIX-like systems such as Linux) are the result of entries in inetd.conf that should have been "commented out" or removed. On the other hand, an omitted entry can cause your system to consume extra memory or swap space, or make it more susceptible to denial of service attacks."

"As the name implies, /etc/inetd.conf is the configuration file for inetd, the "Internet daemon." In the early days of UNIX, when a 10 MB hard drive was considered to be huge and system memory was measured in kilobytes instead of megabytes, inetd was devised as a way to save valuable RAM and disk swap space."

"Prior to inetd, each "daemon" -- that is, a program which provided an Internet service -- had to be in memory, waiting for requests, at all times. But there was a problem: keeping that code loaded and ready to run consumed valuable system resources. As the repertoire of services provided by systems on the Internet (then the ARPANet) grew, systems were in peril of being overrun by daemons, leaving no space for programs that did other work."

"Enter inetd. Acting as a sort of switchboard operator, inetd fields incoming requests for other daemons. When a "call" comes in, inetd starts up a copy of the appropriate daemon and "transfers the call" to it. Thus, no Internet daemon -- other than inetd itself, of course -- must remain in memory when it's not providing a service."

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