services - Internet network services list


   services  is  a  plain  ASCII  file  providing a mapping between human-
   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  be  bound
   to  only 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
   <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 protocols(5) file.   Typical  values  include
             tcp and udp.

   aliases   is an optional space or tab separated list of other names for
             this service.  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.  However, a conservative choice of
   characters should be used  to  minimize  compatibility  problems.   For
   example, 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 behavior should
   not be relied on.)

   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


          The Internet network services list

          Definition of _PATH_SERVICES


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

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


   This page is part of release 4.09 of the Linux  man-pages  project.   A
   description  of  the project, information about reporting bugs, and the
   latest    version    of    this    page,    can     be     found     at

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