services(5) — Linux manual page

NAME | DESCRIPTION | FILES | SEE ALSO | COLOPHON

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

NAME         top

       services - Internet network services list

DESCRIPTION         top

       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.  For example, 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         top

       /etc/services
              The Internet network services list

       <netdb.h>
              Definition of _PATH_SERVICES

SEE ALSO         top

       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         top

       This page is part of release 5.11 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                          2020-04-11                    SERVICES(5)

Pages that refer to this page: getaddrinfo(3)getnameinfo(3)getservent(3)getservent_r(3)nscd(8)rpc.rquotad(8)rsyslogd(8)