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 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.  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

       This  page  is  part  of  release 3.54 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/.