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 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), setser-
       vent(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 imple-
       mentation, and not a rogue service run by a user of the machine.  Well-known port numbers specified by the IANA are  nor-
       mally 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 run-
       ning 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  sensi-
                 tive.

       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 min-
       imize 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 getser-
       vent(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
       This  page  is  part of release 3.25 of the Linux man-pages project.  A description of the project, and information about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                                                      2010-05-22                                                SERVICES(5)