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  be  bound
23       to  only 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.  Again, the names are case sensitive.
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59       Either spaces or tabs may be used to separate the fields.
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61       Comments are started by the hash sign (#) and continue until the end of
62       the line.  Blank lines are skipped.
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64       The  service-name  should  begin in the first column of the file, since
65       leading spaces are not stripped.  service-names can  be  any  printable
66       characters  excluding space and tab.  However, a conservative choice of
67       characters should be used  to  minimize  compatibility  problems.   For
68       example, a-z, 0-9, and hyphen (-) would seem a sensible choice.
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70       Lines  not  matching  this  format  should  not be present in the file.
71       (Currently, they are  silently  skipped  by  getservent(3),  getservby‐
72       name(3),  and  getservbyport(3).   However, this behavior should not be
73       relied on.)
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75       This file might be distributed over a network using a network-wide nam‐
76       ing service like Yellow Pages/NIS or BIND/Hesiod.
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78       A sample services file might look like this:
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80           netstat         15/tcp
81           qotd            17/tcp          quote
82           msp             18/tcp          # message send protocol
83           msp             18/udp          # message send protocol
84           chargen         19/tcp          ttytst source
85           chargen         19/udp          ttytst source
86           ftp             21/tcp
87           # 22 - unassigned
88           telnet          23/tcp
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FILES

91       /etc/services
92              The Internet network services list
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94       <netdb.h>
95              Definition of _PATH_SERVICES
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104       This page is part of release 5.04 of the Linux  man-pages  project.   A
105       description  of  the project, information about reporting bugs, and the
106       latest    version    of    this    page,    can     be     found     at
107       https://www.kernel.org/doc/man-pages/.
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111Linux                             2010-05-22                       SERVICES(5)

NAME

DESCRIPTION

FILES

SEE ALSO

COLOPHON