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1 perry 1 SERVICES
2 !!!SERVICES
3 NAME
4 DESCRIPTION
5 BUGS
6 FILES
7 SEE ALSO
8 ----
9 !!NAME
10
11
12 services - Internet network services list
13 !!DESCRIPTION
14
15
16 __services__ is a plain ASCII file providing a mapping
17 between friendly textual names for internet services, and
18 their underlying assigned port numbers and protocol types.
19 Every networking program should look into this file to get
20 the port number (and protocol) for its service. The C
21 library routines getservent(3),
22 getservbyname(3), getservbyport(3),
23 setservent(3), and endservent(3) support
24 querying this file from programs.
25
26
27 Port numbers are assigned by the IANA (Internet Assigned
28 Numbers Authority), and their current policy is to assign
29 both TCP and UDP protocols when assigning a port number.
30 Therefore, most entries will have two entries, even for TCP
31 only services.
32
33
34 Port numbers below 1024 (so-called 'low numbered' ports) can
35 only be bound to by root (see bind(2), tcp(7),
36 and udp(7).) This is so that clients connecting to
37 low numbered ports can trust that the service running on the
38 port is the standard implementation, and not a rogue service
39 run by a user of the machine. Well-known port numbers
40 specified by the IANA are normally located in this root only
41 space.
42
43
44 The presence of an entry for a service in the
45 __services__ file does not necessarily mean that the
46 service is currently running on the machine. See
47 inetd.conf(5) for the configuration of Internet
48 services offered. Note that not all networking services are
49 started by inetd(8), and so won't appear in
50 inetd.conf(5). In particular, news (NNTP) and mail
51 (SMTP) servers are often initialised from the system boot
52 scripts.
53
54
55 The location of the __services__ file is defined by
56 ___PATH_SERVICES__ in ''/usr/include/netdb.h''. This
57 is usually set to ''/etc/services''.
58
59
60 Each line describes one service, and is of the
61 form:
62
63
64 ''service-name port''__/__''protocol'' [[''aliases
65 ...'']
66
67
68 where:
69
70
71 ''service-name''
72
73
74 is the friendly name the service is known by and looked up
75 under. It is case sensitive. Often, the client program is
76 named after the ''service-name''.
77
78
79 ''port''
80
81
82 is the port number (in decimal) to use for this
83 service.
84
85
86 ''protocol''
87
88
89 is the type of protocol to be used. This field should match
90 an entry in the protocols(5) file. Typical values
91 include __tcp__ and __udp__.
92
93
94 ''aliases''
95
96
97 is an optional space or tab separated list of other names
98 for this service (but see the BUGS section below). Again,
99 the names are case sensitive.
100
101
102 Either spaces or tabs may be used to separate the
103 fields.
104
105
106 Comments are started by the hash sign (#) and continue until
107 the end of the line. Blank lines are skipped.
108
109
110 The ''service-name'' should begin in the first column of
111 the file, since leading spaces are not stripped.
112 ''service-names'' can be any printable characters
113 excluding space and tab, however, a conservative choice of
114 characters should be used to minimise inter-operability
115 problems. Eg: a-z, 0-9, and hyphen (-) would seem a sensible
116 choice.
117
118
119 Lines not matching this format should not be present in the
120 file. (Currently, they are silently skipped by
121 getservent(3), getservbyname(3), and
122 getservbyport(3). However, this behaviour should not
123 be relied on.)
124
125
126 As a backwards compatibility feature, the slash (/) between
127 the ''port'' number and ''protocol'' name can in fact
128 be either a slash or a comma (,). Use of the comma in modern
129 installations is depreciated.
130
131
132 This file might be distributed over a network using a
133 network-wide naming service like Yellow Pages/NIS or
134 BIND/Hesiod.
135
136
137 A sample __services__ file might look like
138 this:
139
140
141 netstat 15/tcp
142 qotd 17/tcp quote
143 msp 18/tcp # message send protocol
144 msp 18/udp # message send protocol
145 chargen 19/tcp ttytst source
146 chargen 19/udp ttytst source
147 ftp 21/tcp
148 # 22 - unassigned
149 telnet 23/tcp
150 !!BUGS
151
152
153 There is a maximum of 35 aliases, due to the way the
154 getservent(3) code is written.
155
156
157 Lines longer than __BUFSIZ__ (currently 1024) characters
158 will be ignored by getservent(3),
159 getservbyname(3), and getservbyport(3).
160 However, this will also cause the next line to be
161 mis-parsed.
162 !!FILES
163
164
165 ''/etc/services''
166
167
168 The Internet network services list
169
170
171 ''/usr/include/netdb.h''
172
173
174 Definition of ___PATH_SERVICES__
175 !!SEE ALSO
176
177
178 getservent(3), getservbyname(3),
179 getservbyport(3), setservent(3),
180 endservent(3), protocols(5), listen(2),
181 inetd.conf(5), inetd(8)
182
183
184 Assigned Numbers RFC, most recently RFC 1700, (AKA
185 STD0002)
186
187
188 Guide to Yellow Pages Service
189
190
191 Guide to BIND/Hesiod Service
192 ----
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