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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 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  <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.  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
       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

FILES

       /etc/services
              The Internet network services list

       <netdb.h>
              Definition of _PATH_SERVICES

SEE ALSO

       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)

COLOPHON

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       project,  and information about reporting bugs, can be found at http://man7.org/linux/man-
       pages/.