services(5)

1SERVICES(5)                Linux Programmer's Manual               SERVICES(5)
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NAME

6       services - Internet network services list
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DESCRIPTION

9       services  is  a  plain  ASCII  file  providing a mapping between human-
10       friendly textual names for  internet  services,  and  their  underlying
11       assigned  port  numbers  and  protocol types.  Every networking program
12       should look into this file to get the port number  (and  protocol)  for
13       its  service.   The C library routines getservent(3), getservbyname(3),
14       getservbyport(3), setservent(3),  and  endservent(3)  support  querying
15       this file from programs.
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17       Port  numbers  are  assigned  by  the  IANA  (Internet Assigned Numbers
18       Authority), and their current policy is to assign both TCP and UDP pro‐
19       tocols when assigning a port number.  Therefore, most entries will have
20       two entries, even for TCP-only services.
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22       Port numbers below 1024 (so-called "low numbered" ports)  can  only  be
23       bound to by root (see bind(2), tcp(7), and udp(7)).  This is so clients
24       connecting to low numbered ports can trust that the service running  on
25       the port is the standard implementation, and not a rogue service run by
26       a user of the machine.  Well-known port numbers specified by  the  IANA
27       are normally located in this root-only space.
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29       The  presence  of  an entry for a service in the services file does not
30       necessarily mean that the service is currently running on the  machine.
31       See  inetd.conf(5)  for the configuration of Internet services offered.
32       Note that not all networking services are started by inetd(8),  and  so
33       won't  appear  in  inetd.conf(5).   In particular, news (NNTP) and mail
34       (SMTP) servers are often initialized from the system boot scripts.
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36       The location of the services  file  is  defined  by  _PATH_SERVICES  in
37       <netdb.h>.  This is usually set to /etc/services.
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39       Each line describes one service, and is of the form:
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41              service-name   port/protocol   [aliases ...]
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43       where:
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45       service-name
46                 is  the  friendly  name the service is known by and looked up
47                 under.  It is case sensitive.  Often, the client  program  is
48                 named after the service-name.
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50       port      is the port number (in decimal) to use for this service.
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52       protocol  is  the type of protocol to be used.  This field should match
53                 an entry in the protocols(5) file.   Typical  values  include
54                 tcp and udp.
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56       aliases   is an optional space or tab separated list of other names for
57                 this service (but see the BUGS section  below).   Again,  the
58                 names are case sensitive.
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60       Either spaces or tabs may be used to separate the fields.
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62       Comments are started by the hash sign (#) and continue until the end of
63       the line.  Blank lines are skipped.
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65       The service-name should begin in the first column of  the  file,  since
66       leading  spaces  are  not stripped.  service-names can be any printable
67       characters excluding space and tab.  However, a conservative choice  of
68       characters  should  be  used to minimize compatibility problems.  E.g.,
69       a-z, 0-9, and hyphen (-) would seem a sensible choice.
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71       Lines not matching this format should  not  be  present  in  the  file.
72       (Currently,  they  are  silently  skipped  by getservent(3), getservby‐
73       name(3), and getservbyport(3).  However, this behavior  should  not  be
74       relied on.)
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76       This file might be distributed over a network using a network-wide nam‐
77       ing service like Yellow Pages/NIS or BIND/Hesiod.
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79       A sample services file might look like this:
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81              netstat         15/tcp
82              qotd            17/tcp          quote
83              msp             18/tcp          # message send protocol
84              msp             18/udp          # message send protocol
85              chargen         19/tcp          ttytst source
86              chargen         19/udp          ttytst source
87              ftp             21/tcp
88              # 22 - unassigned
89              telnet          23/tcp
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FILES

92       /etc/services
93              The Internet network services list
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95       <netdb.h>
96              Definition of _PATH_SERVICES
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COLOPHON

105       This  page  is  part of release 3.22 of the Linux man-pages project.  A
106       description of the project, and information about reporting  bugs,  can
107       be found at http://www.kernel.org/doc/man-pages/.
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111Linux                             2008-09-23                       SERVICES(5)

NAME

DESCRIPTION

FILES

SEE ALSO

COLOPHON