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RedHat 9 (Linux i386) - man page for services (redhat section 5)

SERVICES(5)			    Linux Programmer's Manual			      SERVICES(5)

       services - Internet network services list

       services  is  a	plain  ASCII  file providing a mapping between friendly textual names for
       internet services, and their underlying assigned port numbers and  protocol  types.  Every
       networking  program  should  look into this file to get the port number (and protocol) for
       its service.  The C library routines  getservent(3),  getservbyname(3),	getservbyport(3),
       setservent(3), and endservent(3) support querying this file from programs.

       Port  numbers  are  assigned  by the IANA (Internet Assigned Numbers Authority), and their
       current policy is to assign both TCP and UDP  protocols	when  assigning  a  port  number.
       Therefore, most entries will have two entries, even for TCP only services.

       Port numbers below 1024 (so-called 'low numbered' ports) can only be bound to by root (see
       bind(2), tcp(7), and udp(7)).  This is so clients connecting to	low  numbered  ports  can
       trust that the service running on the port is the standard implementation, and not a rogue
       service run by a user of the machine.  Well-known port numbers specified by the	IANA  are
       normally located in this root-only space.

       The presence of an entry for a service in the services file does not necessarily mean that
       the service is currently running on the machine. See inetd.conf(5) for  the  configuration
       of  Internet  services  offered.  Note  that  not  all  networking services are started by
       inetd(8), and so won't appear in inetd.conf(5).	 In  particular,  news	(NNTP)	and  mail
       (SMTP) servers are often initialized from the system boot scripts.

       The  location  of  the services file is defined by _PATH_SERVICES in /usr/include/netdb.h.
       This is usually set to /etc/services.

       Each line describes one service, and is of the form:

	      service-name   port/protocol   [aliases ...]


		 is the friendly name the service is known by and looked up  under.  It  is  case
		 sensitive. Often, the client program is named after the service-name.

       port	 is the port number (in decimal) to use for this service.

       protocol  is the type of protocol to be used. This field should match an entry in the pro-
		 tocols(5) file. Typical values include tcp and udp.

       aliases	 is an optional space or tab separated list of other names for this service  (but
		 see the BUGS section below). Again, the names are case sensitive.

       Either spaces or tabs may be used to separate the fields.

       Comments  are  started  by the hash sign (#) and continue until the end of the line. Blank
       lines are skipped.

       The service-name should begin in the first column of the file, since  leading  spaces  are
       not stripped.  service-names can be any printable characters excluding space and tab. How-
       ever, a conservative choice of characters should be  used  to  minimize	inter-operability
       problems. E.g., a-z, 0-9, and hyphen (-) would seem a sensible choice.

       Lines  not  matching  this  format should not be present in the file. (Currently, they are
       silently skipped by getservent(3), getservbyname(3), and getservbyport(3).  However,  this
       behaviour should not be relied on.)

       As  a  backwards compatibility feature, the slash (/) between the port number and protocol
       name can in fact be either a slash or a comma (,). Use of the comma  in	modern	installa-
       tions is depreciated.

       This  file  might  be  distributed over a network using a network-wide naming service like
       Yellow Pages/NIS or BIND/Hesiod.

       A sample services file might look like this:

	      netstat	      15/tcp
	      qotd	      17/tcp	      quote
	      msp	      18/tcp	      # message send protocol
	      msp	      18/udp	      # message send protocol
	      chargen	      19/tcp	      ttytst source
	      chargen	      19/udp	      ttytst source
	      ftp	      21/tcp
	      # 22 - unassigned
	      telnet	      23/tcp

       There is a maximum of 35 aliases, due to the way the getservent(3) code is written.

       Lines longer than BUFSIZ (currently 1024) characters will  be  ignored  by  getservent(3),
       getservbyname(3), and getservbyport(3).	However, this will also cause the next line to be

	      The Internet network services list

	      Definition of _PATH_SERVICES

       getservent(3), getservbyname(3), getservbyport(3),  setservent(3),  endservent(3),  proto-
       cols(5), listen(2), inetd.conf(5), inetd(8)

       Assigned Numbers RFC, most recently RFC 1700, (AKA STD0002)

       Guide to Yellow Pages Service

       Guide to BIND/Hesiod Service

Linux					    1996-01-11				      SERVICES(5)

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