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SERVICES
!!!SERVICES
NAME
DESCRIPTION
BUGS
FILES
SEE ALSO
----
!!NAME


services - Internet network services list
!!DESCRIPTION


__services__ is a plain ASCII file providing a mapping
between 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
only be bound to by root (see bind(2), tcp(7),
and udp(7).) This is so that 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 initialised from the system boot
scripts.


The location of the __services__ file is defined by
___PATH_SERVICES__ in ''/usr/include/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 (but see the BUGS section below). 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 minimise inter-operability
problems. Eg: 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 behaviour should not
be relied on.)


As a backwards compatibility feature, the slash (/) between
the ''port'' number and ''protocol'' name can in fact
be either a slash or a comma (,). Use of the comma in modern
installations is depreciated.


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
!!BUGS


There is a maximum of 35 aliases, due to the way the
getservent(3) code is written.


Lines longer than __BUFSIZ__ (currently 1024) characters
will be ignored by getservent(3),
getservbyname(3), and getservbyport(3).
However, this will also cause the next line to be
mis-parsed.
!!FILES


''/etc/services''


The Internet network services list


''/usr/include/netdb.h''


Definition of ___PATH_SERVICES__
!!SEE ALSO


getservent(3), getservbyname(3),
getservbyport(3), setservent(3),
endservent(3), protocols(5), listen(2),
inetd.conf(5), inetd(8)


Assigned Numbers RFC, most recently RFC 1700, (AKA
STD0002)


Guide to Yellow Pages Service


Guide to BIND/Hesiod Service
----
17 pages link to services(5):
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Last edited on Tuesday, June 4, 2002 12:30:41 am by "perry"
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