services

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

NAME
       services - Internet network services list

DESCRIPTION
       services  is  a  plain  ASCII  file  providing a mapping between human-
       friendly textual names for internet services, and their underlying  as-
       signed  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 Au-
       thority), and their current policy is to assign both TCP and UDP proto-
       cols  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 ...]

       where:

       service-name
                 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  ex-
       ample, 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),  getservby-
       name(3),  and  getservbyport(3).   However, this behavior should not be
       relied on.)

       This file might be distributed over a network using a network-wide nam-
       ing 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

FILES
       /etc/services
              The Internet network services list

       <netdb.h>
              Definition of _PATH_SERVICES

SEE ALSO
       listen(2),  endservent(3),  getservbyname(3), getservbyport(3), getser-
       vent(3), setservent(3), inetd.conf(5), protocols(5), inetd(8)

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

COLOPHON
       This page is part of release 5.05 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
       https://www.kernel.org/doc/man-pages/.

Linux                             2010-05-22                       SERVICES(5)