services(4) Kernel Interfaces Manual services(4)NAME
services - Defines the sockets and protocols used for Internet services
SYNOPSIS
/etc/services
DESCRIPTION
The /etc/services file associates Internet service names and aliases with the port number and protocol used by the service. Each service
is listed in this file on a single line of the form: ServiceName PortNumber/ProtocolName Aliases
The fields contain the following information: The official Internet service name. The socket port number used for the service and the
transport protocol used for the service. A list of unofficial service names.
Items on a line are separated by spaces or tabs. Comments begin with a # (number sign) and continue to the end of the line.
EXAMPLES
Entries in the /etc/services file for the inetd internal services might look like this: echo 7/tcp echo 7/udp discard
9/tcp sink null discard 9/udp sink null daytime 13/tcp daytime 13/udp chargen 19/tcp ttytst source
chargen 19/tcp ttytst source ftp 21/tcp time 37/tcp timeserver time 37/udp timeserver
RELATED INFORMATION
Functions: endservent(3), getservbyname(3), getservbyport(3), getservent(3), setservent(3)
The RFC923 specification. delim off
services(4)
Check Out this Related Man Page
SERVICES(5) Linux Programmer's Manual SERVICES(5)NAME
services - Internet network services list
DESCRIPTION
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 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 proto-
cols 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'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 _PATH_SERVICES in <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. 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 minimize compatibility problems. E.g.,
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), getservby-
name(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.
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
FILES
/etc/services
The Internet network services list
<netdb.h>
Definition of _PATH_SERVICES
SEE ALSO listen(2), endservent(3), getservbyname(3), getservbyport(3), getservent(3), setservent(3), inetd.conf(5), protocols(5), inetd(8)
Assigned Numbers RFC, most recently RFC 1700, (AKA STD0002).
COLOPHON
This page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
Linux 2010-05-22 SERVICES(5)