TranslateProject/sources/tech/20190109 Understanding -etc-services file in Linux.md

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[#]: collector: (lujun9972)
[#]: translator: ( )
[#]: reviewer: ( )
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[#]: subject: (Understanding /etc/services file in Linux)
[#]: via: (https://kerneltalks.com/linux/understanding-etc-services-file-in-linux/)
[#]: author: (kerneltalks https://kerneltalks.com)
Understanding /etc/services file in Linux
======
Article which helps you to understand /etc/services file in Linux. Learn about content, format & importance of this file.
![/etc/services file in Linux][1]
/etc/services file in Linux
Internet daemon is important service in Linux world. It takes care of all network services with the help of `/etc/services` file. In this article we will walk you through content, format of this file and what it means to a Linux system.
`/etc/services` file contains list of network services and ports mapped to them. `inetd` or `xinetd` looks at these details so that it can call particular program when packet hits respective port and demand for service.
As a normal user you can view this file since file is world readable. To edit this file you need to have root privileges.
```
$ ll /etc/services
-rw-r--r--. 1 root root 670293 Jun 7 2013 /etc/services
```
### `/etc/services` file format
```
service-name port/protocol [aliases..] [#comment]
```
Last two fields are optional hence denoted in `[` `]`
where
* service-name is name of the network service. e.g. [telnet][2], [ftp][3] etc.
* port/protocol is port being used by that network service (numerical value) and protocol (TCP/UDP) used for communication by service.
* alias is alternate name for service.
* comment is note or description you can add to service. Starts with `#` mark
### Sample` /etc/services` file
```
# Each line describes one service, and is of the form:
#
# service-name port/protocol [aliases ...] [# comment]
tcpmux 1/tcp # TCP port service multiplexer
rje 5/tcp # Remote Job Entry
echo 7/udp
discard 9/udp sink null
```
Here, you can see use of optional last two fields as well. `discard` service has alternate name as `sink` or `null`.
--------------------------------------------------------------------------------
via: https://kerneltalks.com/linux/understanding-etc-services-file-in-linux/
作者:[kerneltalks][a]
选题:[lujun9972][b]
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[a]: https://kerneltalks.com
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[1]: https://i2.wp.com/kerneltalks.com/wp-content/uploads/2019/01/undestanding-etc-service-file-in-linux.png?ssl=1
[2]: https://kerneltalks.com/config/configure-telnet-server-linux/
[3]: https://kerneltalks.com/config/ftp-server-configuration-steps-rhel-6/