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       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  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 ...]


                 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 (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.  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


              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)


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