-.\" Hey Emacs! This file is -*- nroff -*- source.
-.\"
.\" This manpage is Copyright (C) 1996 Austin Donnelly <and1000@cam.ac.uk>,
-.\" with additional material (c) 1995 Martin Schulze <joey@infodrom.north.de>
-.\"
-.\" Permission is granted to make and distribute verbatim copies of this
-.\" manual provided the copyright notice and this permission notice are
-.\" preserved on all copies.
+.\" with additional material Copyright (c) 1995 Martin Schulze
+.\" <joey@infodrom.north.de>
.\"
-.\" Permission is granted to copy and distribute modified versions of this
-.\" manual under the conditions for verbatim copying, provided that the
-.\" entire resulting derived work is distributed under the terms of a
-.\" permission notice identical to this one.
-.\"
-.\" Since the Linux kernel and libraries are constantly changing, this
-.\" manual page may be incorrect or out-of-date. The author(s) assume no
-.\" responsibility for errors or omissions, or for damages resulting from
-.\" the use of the information contained herein. The author(s) may not
-.\" have taken the same level of care in the production of this manual,
-.\" which is licensed free of charge, as they might when working
-.\" professionally.
-.\"
-.\" Formatted or processed versions of this manual, if unaccompanied by
-.\" the source, must acknowledge the copyright and authors of this work.
+.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.\" This manpage was made by merging two independently written manpages,
.\" one written by Martin Schulze (18 Oct 95), the other written by
.\" Thu Jan 11 12:14:41 1996 Austin Donnelly <and1000@cam.ac.uk>
.\" * Merged two services(5) manpages
.\"
-.TH SERVICES 5 1996-01-11 "Linux" "Linux Programmer's Manual"
+.TH SERVICES 5 2020-04-11 "Linux man-pages (unreleased)"
.SH NAME
services \- Internet network services list
.SH DESCRIPTION
.B services
-is a plain ASCII file providing a mapping between friendly textual
+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
+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
.BR getservent (3),
.BR getservbyname (3),
.BR getservbyport (3),
.BR setservent (3),
-and
+and
.BR endservent (3)
support querying this file from programs.
-
+.PP
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
+protocols when assigning a port number.
+Therefore, most entries will
+have two entries, even for TCP-only services.
+.PP
+Port numbers below 1024 (so-called "low numbered" ports) can be
+bound to only by root (see
.BR bind (2),
.BR tcp (7),
-and
+and
.BR 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
+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.
+.PP
+The presence of an entry for a service in the
.B services
file does not necessarily mean that the service is currently running
-on the machine. See
+on the machine.
+See
.BR inetd.conf (5)
-for the configuration of Internet services offered. Note that not all
+for the configuration of Internet services offered.
+Note that not all
networking services are started by
.BR inetd (8),
and so won't appear in
.BR inetd.conf (5).
In particular, news (NNTP) and mail (SMTP) servers are often
initialized from the system boot scripts.
-
+.PP
The location of the
.B services
file is defined by
.B _PATH_SERVICES
in
-.IR /usr/include/netdb.h "."
+.IR <netdb.h> "."
This is usually set to
.IR /etc/services "."
-
+.PP
Each line describes one service, and is of the form:
.IP
\f2service-name\ \ \ port\f3/\f2protocol\ \ \ \f1[\f2aliases ...\f1]
.TP
where:
-.TP 10
+.TP
.I 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
+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
.IR service-name "."
.TP
.I port
is the port number (in decimal) to use for this service.
.TP
.I protocol
-is the type of protocol to be used. This field should match an entry
+is the type of protocol to be used.
+This field should match an entry
in the
.BR protocols (5)
-file. Typical values include
+file.
+Typical values include
.B tcp
and
.BR udp .
.TP
.I 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
+service.
+Again, the names are case
sensitive.
.PP
-
Either spaces or tabs may be used to separate the fields.
-
+.PP
Comments are started by the hash sign (#) and continue until the end
-of the line. Blank lines are skipped.
-
+of the line.
+Blank lines are skipped.
+.PP
The
.I service-name
should begin in the first column of the file, since leading spaces are
not stripped.
.I service-names
-can be any printable characters excluding space and tab. However,
-a conservative choice of characters should be used to minimize
-inter-operability problems. E.g., a\-z, 0\-9, and hyphen (\-) would seem a
+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.
-
+.PP
Lines not matching this format should not be present in the
-file. (Currently, they are silently skipped by
+file.
+(Currently, they are silently skipped by
.BR getservent (3),
.BR getservbyname (3),
and
.BR getservbyport (3).
-However, this behaviour should not be relied on.)
-
-As a backwards compatibility feature, the slash (/) between the
-.I port
-number and
-.I protocol
-name can in fact be either a slash or a comma (,). Use of the comma in
-modern installations is depreciated.
-
+However, this behavior should not be relied on.)
+.PP
+.\" The following is not true as at glibc 2.8 (a line with a comma is
+.\" ignored by getservent()); it's not clear if/when it was ever true.
+.\" As a backward compatibility feature, the slash (/) between the
+.\" .I port
+.\" number and
+.\" .I protocol
+.\" name can in fact be either a slash or a comma (,).
+.\" Use of the comma in
+.\" modern installations is deprecated.
+.\"
This file might be distributed over a network using a network-wide
naming service like Yellow Pages/NIS or BIND/Hesiod.
-
+.PP
A sample
.B services
file might look like this:
-.RS
-.nf
-.sp
-.ta 3i
+.PP
+.in +4n
+.EX
netstat 15/tcp
qotd 17/tcp quote
msp 18/tcp # message send protocol
ftp 21/tcp
# 22 \- unassigned
telnet 23/tcp
-.sp
-.fi
-.RE
-.SH BUGS
-There is a maximum of 35 aliases, due to the way the
-.BR getservent (3)
-code is written.
-
-Lines longer than
-.B BUFSIZ
-(currently 1024) characters will be ignored by
-.BR getservent (3),
-.BR getservbyname (3),
-and
-.BR getservbyport (3).
-However, this will also cause the next line to be mis-parsed.
+.EE
+.in
.SH FILES
.TP
.I /etc/services
The Internet network services list
.TP
-.I /usr/include/netdb.h
+.I <netdb.h>
Definition of
.B _PATH_SERVICES
-.SH "SEE ALSO"
+.\" .SH BUGS
+.\" It's not clear when/if the following was ever true;
+.\" it isn't true for glibc 2.8:
+.\" There is a maximum of 35 aliases, due to the way the
+.\" .BR getservent (3)
+.\" code is written.
+.\"
+.\" It's not clear when/if the following was ever true;
+.\" it isn't true for glibc 2.8:
+.\" Lines longer than
+.\" .B BUFSIZ
+.\" (currently 1024) characters will be ignored by
+.\" .BR getservent (3),
+.\" .BR getservbyname (3),
+.\" and
+.\" .BR getservbyport (3).
+.\" However, this will also cause the next line to be mis-parsed.
+.SH SEE ALSO
.BR listen (2),
.BR endservent (3),
.BR getservbyname (3),
.BR inetd.conf (5),
.BR protocols (5),
.BR inetd (8)
-
-Assigned Numbers RFC, most recently RFC 1700, (AKA STD0002)
-
-Guide to Yellow Pages Service
-
-Guide to BIND/Hesiod Service
+.PP
+Assigned Numbers RFC, most recently RFC\ 1700, (AKA STD0002).
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