Section (5) services
services — Internet network services list
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
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_zsingle_quotesz_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
This is usually set to
Each line describes one service, and is of the form:
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
is the port number (in decimal) to use for this service.
is the type of protocol to be used. This field should match an entry in the protocols(5) file. Typical values include
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.
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.
services file might look like
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
Assigned Numbers RFC, most recently RFC 1700, (AKA STD0002).
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This manpage is Copyright (C) 1996 Austin Donnelly <and1000cam.ac.uk>,
with additional material Copyright (c) 1995 Martin Schulze
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This manpage was made by merging two independently written manpages,
one written by Martin Schulze (18 Oct 95), the other written by
Austin Donnelly, (9 Jan 96).
Thu Jan 11 12:14:41 1996 Austin Donnelly <and1000cam.ac.uk>
* Merged two services(5) manpages