服务器相关实用Linux主题深度解析

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"《实用Linux主题》(Practical Linux Topics)是由Chris Binnie编著的一本深入探讨Linux领域的专业书籍。该书定位为实用指南，适合那些希望学习并长期参考服务器相关技术的读者。作者以其在Linux领域的专家身份，提供了全面而详实的内容，涵盖了广泛的Linux主题，确保读者能够掌握实践中的关键技能。书中不仅包含了基础概念的阐述，还深入到诸如云计算、服务器管理、网络配置、安全实践、性能优化等高级主题。通过阅读本书，读者可以了解到如何在实际环境中有效地运用Linux，无论是企业级应用还是个人开发项目，都能从中受益。每一章节都经过精心设计，以便读者能够在理论与实践之间建立牢固的联系。版权方面，所有内容受到保护，未经Springer出版社许可，不得擅自复制或传播，包括但不限于翻译、再版、复用插图、朗读、广播、微缩胶片复制、电子适应性转换或任何形式的信息存储和检索。只有在符合版权法和出版商所在地当前版本的规定下，且专为购买者计算机系统上的个人使用而准备的学术评论或学术分析材料才可例外。《实用Linux主题》是一本不可多得的参考资料，对于想要提升Linux技能的读者来说，无论是初学者还是经验丰富的专业人士，都将从中获得宝贵的知识和实战经验。通过这本书，读者不仅可以掌握Linux的基础操作，还能了解如何将其应用于现代IT环境中的云服务，从而提高工作效率和业务效能。"

Chapter 1

Real Time Network Statistics

with Iftop

Monitoring network connections certainly can be frustrating, mainly because they can be established and

then disappear within a matter of seconds. In this chapter, I show you how to achieve a Zen like approach

to monitoring network connections on your servers using a command line–based tool called iftop. I then

finish by walking through the creation of a configuration file that you can use again on different servers once

you have your monitoring set up as you prefer.

Monitoring Network Connections with netstat

The netstat command-line tool has been a staple among system admins. Although rich in features,

including an auto-refresh parameter (continuous mode), netstat is certainly not designed to do much

more than output raw numbers and names (from hosts and ports). To run netstat in continuous mode, for

example, you can use:

# netstat c

I usually end up running it alongside watch to give me the kind of clean screen refreshes I need for

different scenarios; for example:

# watch n2 "netstat tu"

In this example, watch lets me configure a two-second gap prior to running the command again and

updating its output (see Figure1-1).

Chapter 1 ■ real time Network StatiStiCS with iftop

On the right side, you can see three columns. The excellent iftop refers to this as its display order and

the columns deal with different time-delay averages. By default, this appears (at least) to be two-second,

ten-second, and forty-second averages. These values can be configured separately, so don’t let that confuse

you too much initially. In addition, it’s easy to change the overall display using those columns by pressing

the 1, 2, or 3 keys to respectively filter by the aforementioned 2s, 10s, or 40s averages.

As an aside, a two-second average is really short; I love it having come from a background filled with

what felt like lengthy five-minute SNMP averages. I can see very quickly what’s just changed on the network

and although two seconds isn’t real-time, it’s very close to it and certainly has its place on today’s busy

Internet. I find that it’s just long enough for you to be able to spot something without worrying about freezing

the screen in case you missed it.

When you’re running the default config without specifying any options, iftop outputs the busiest hosts

in the last ten seconds (in other words, by using a ten-second average). It also groups hosts in pairs to choose

the busiest pair of combined inbound and outbound traffic.

Finally, at the end of the output, you are presented with a number of totals. These include useful

statistics, such as the amount of data transferred in megabytes (MB) as well as forty-second averages of

traffic, usually in megabits (Mb), but also sometimes in kb for kilobytes.

Controlling iftop from the Keyboard

In addition to providing a slick graphical display, even through an SSH terminal, iftop lets you modify

your configuration at the press of a key. For example, in the course of a sysadmin’s work day, you could be

checking all sorts of bad networking habits: from monitoring the misconfiguration of a network interface to

mitigating a hideously hazardous ARP storm. With iftop, you can cycle through a number of options and

confidently choose a config parameter to suit your current scenario instantly.

Here are some examples of how iftop can make your sysadmin life easier at the press of key:

• To change the source and destination displays, press the s key or the d key while

iftop is running. This helps isolate who is sending what, especially if iftop is being

run on a Linux router (which I’ll touch in “Using iftop on Busy Routers” later in this

chapter) and forwarding traffic.

• To quickly see which ports are in use, press the p key. You can also use the Shift+S

and Shift+D keys to expose source and destination ports, respectively. Figure1-4

demonstrates how friendly iftop is with its options and how it dutifully reports, in

the top-left of the screen, the result of the keypress that it has just received.

• To cycle through several different displays (similar to horizontal bar graphs), press

the t key.

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