Xinetd

Last updated
xinetd
Developer(s) Rob Braun
Final release
2.3.15 / 9 May 2012;11 years ago (2012-05-09)
Repository github.com/xinetd-org/xinetd
Written in C, Shell [1]
Operating system Unix-like
Type Daemon
License Open-source [2]
Website web.archive.org/web/20051227095035/http://www.xinetd.org:80/ [ dead link ]

In computer networking, xinetd (Extended Internet Service Daemon) is an open-source super-server daemon which runs on many Unix-like systems, and manages Internet-based connectivity. [3]

Contents

It offers a more secure alternative to the older inetd ("the Internet daemon"), which most modern Linux distributions have deprecated. [4]

Description

xinetd listens for incoming requests over a network and launches the appropriate service for that request. [5] Requests are made using port numbers as identifiers and xinetd usually launches another daemon to handle the request. [6] It can be used to start services with both privileged and non-privileged port numbers.

xinetd features access control mechanisms such as TCP Wrapper ACLs, extensive logging capabilities, and the ability to make services available based on time. It can place limits on the number of servers that the system can start, and has deployable defense mechanisms to protect against port scanners, among other things.

On some implementations of Mac OS X, this daemon starts and maintains various Internet-related services, including FTP and telnet. As an extended form of inetd, it offers enhanced security. It replaced inetd in Mac OS X v10.3, and subsequently launchd replaced it in Mac OS X v10.4. However, Apple has retained inetd for compatibility purposes.

Configuration

Configuration of xinetd resides in the default configuration file /etc/xinetd.conf, and configuration of the services it supports resides in configuration files stored in the /etc/xinetd.d directory. The configuration for each service usually includes a switch to control whether xinetd should enable or disable the service.

An example configuration file for the RFC 868 time server:

  # default: off # description: An RFC 868 time server. This protocol provides a # site-independent, machine readable date and time. The Time service sends back # to the originating source the time in seconds since midnight on January first # 1900. # This is the tcp version. service time {         disable         = yes         type            = INTERNAL         id              = time-stream         socket_type     = stream         protocol        = tcp         user            = root         wait            = no }  # This is the udp version. service time {         disable         = yes         type            = INTERNAL         id              = time-dgram         socket_type     = dgram         protocol        = udp         user            = root         wait            = yes }

The lines with the "#" character at the beginning are comments without any effect on the service. There are two service versions: the first one is based on the Transmission Control Protocol (TCP), the second one is based on the User Datagram Protocol (UDP). The type and planned usage of a service determines the necessary core protocol. In a simple way, the UDP cannot handle huge data transmissions, because it lacks the abilities to rearrange packages in a specified order or guarantee their integrity, but it is faster than TCP. TCP has these functions, but it is slower. There are two columns in each version inside the braces. The first is the type of option, the second is the applied variable.

The disable option is a switch to run a service or not. In most cases, the default state is yes. To activate the service, change it to no.

There are three types of services. The type is INTERNAL if the service is provided by xinetd, RPC when it based on Remote procedure call (commonly listed in the /etc/rpc file), or it can be UNLISTED when the service is neither in the /etc/services nor in the /etc/rpc files.

The id is the unique identifier of the service.

The socket_type determines the way of data transmission through the service. There are three types: stream, dgram and raw. This last one is useful when we want to establish a service based on a non-standard protocol.

With the user option, it is possible to choose a user to be the owner of the running service. It is highly recommended to choose a non-root user for security reasons.

When the wait is on yes, the xinetd will not receive a request for the service if it has a connection. So, the number of connections is limited to one. It provides very good protection when we want to establish only one connection per time.

There are many more options available for xinetd. In most Linux distributions, the full list of possible options and their description is accessible with a "man xinetd.conf" command.

To apply the new configuration, a SIGHUP signal must be sent to the xinetd process to make it re-read the configuration files. This can be achieved with the following command: kill -SIGHUP "PID". PID is the actual process identifier number of the xinetd, which can be obtained with the command pgrep xinetd. [7] [8]

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References

  1. ↑ "xinetd-org/xinetd". GitHub . Retrieved 2014-07-10.
  2. ↑ "COPYRIGHT". GitHub . 2003-02-19. Retrieved 2014-07-10.
  3. ↑ Wells, Nicholas (2000). "4: Using Simple Network Services". Guide to Linux Installation and Administration. Vol. 1. Boston, Massachusetts: Cengage Learning EMEA. p. 167. ISBN   9780619000974 . Retrieved 2017-07-03. [...] the superserver (also called a metaserver) [...] listens on multiple network ports and starts the appropriate service when a client connection arrives for that port. The most widely used superserver program is called inetd, for Internet daemon. Another superserver that is gaining in popularity is xinetd, for extended Internet daemon [...].
  4. ↑ Smith, Roderick W. (2001). "Networking". Linux Study Guide. Sybex Press. p.  365. ISBN   0-7821-2939-0.
  5. ↑ Negus, C. (2002). "Running Network Services". Red hat Linux 8 Bible. Wiley Publishing Inc. p. 1007. ISBN   0-7645-4968-5.
  6. ↑ "Ubuntu Manpage: xinetd - the extended Internet services daemon". Ubuntu . 14 June 2001. Archived from the original on 23 September 2019. Retrieved 21 April 2020. Because of the way it operates, xinetd (as well as inetd) is also referred to as a super-server. (...) So far, the only reason for the existence of a super-server was to conserve system resources by avoiding to fork a lot of processes which might be dormant for most of their lifetime.
  7. ↑ Linux man page: xinetd.conf(5) http://linux.die.net/man/5/xinetd.conf
  8. ↑ Pere, László (2005). "Hálozati szolgáltatások". GNU/Linux rendszerek üzemeltetése II. Kiskapu Kft. (Hungary). pp. 107–136. ISBN   963-9301-98-1.
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