Linux系统管理员指南1998版

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"Linux系统管理1998版" 这篇文档是"The Linux System Administrators' Guide"的1998年版本，由Lars Wirzenius和Joanna Oja撰写，是一份面向Linux系统管理初学者的指南。尽管版本较旧，但这份指南提供了一个对Linux系统管理的基础介绍。LDP（Linux Documentation Project）是该文档的来源，但现在可能已经有许多更新和更完善的替代资源可以在tldp.org找到。文档内容涵盖了如何管理和维护Linux系统的基础知识，包括但不限于： 1. **系统安装与配置**：指导读者如何安装Linux操作系统，设置网络连接，以及配置系统的基本服务，如DNS解析、文件共享等。 2. **用户与权限管理**：解释了Linux的用户和组概念，如何创建、管理用户账户，以及理解并应用文件权限和访问控制列表（ACL）。 3. **软件包管理**：介绍了早期的软件包管理系统，如RPM（Red Hat Package Manager）或DEB（Debian Package），以及如何安装、升级和卸载软件。 4. **系统日志和监控**：讲解了如何使用syslog收集和分析系统日志，以及如何通过监控工具检查系统性能和稳定性。 5. **磁盘管理**：涵盖了分区、格式化、挂载文件系统，以及如何备份和恢复数据。 6. **进程管理**：讨论了如何启动、停止、查看和控制运行在系统中的进程，以及调度任务和理解进程优先级。 7. **网络服务**：介绍了一些常见的服务器配置，如HTTP服务器（Apache）、FTP服务器、邮件服务器等，以及如何防火墙规则来保护系统。 8. **Shell脚本编程**：简要介绍了Bash shell，以及如何编写简单的脚本来自动化系统任务。 9. **故障排除**：提供了针对常见问题的诊断方法，如系统崩溃、硬件故障、软件冲突等。 10. **安全**：讨论了Linux系统的安全实践，包括设置强密码、使用SSH进行安全远程访问、以及防火墙策略。虽然这份文档是1998年的，但其中的一些核心概念和技术仍然是现代Linux系统管理的基础。然而，随着时间的推移，许多工具和技术（例如软件包管理器、系统日志工具、安全实践）已经发生了变化，因此，对于新手来说，查阅最新版本的文档将更加有益。

Chapter 2. Overview of a Linux System

graphical user interface can be implemented. The three most popular user interface styles implemented

over X are Athena, Motif, and Open Look.

Networking

Networking is the act of connecting two or more computers so that they can communicate with each

other. The actual methods of connecting and communicating are slightly complicated, but the end result

is very useful.

UNIX operating systems have many networking features. Most basic services (ﬁlesystems, printing,

backups, etc) can be done over the network. This can make system administration easier, since it allows

centralized administration, while still reaping in the beneﬁts of microcomputing and distributed

computing, such as lower costs and better fault tolerance.

However, this book merely glances at networking; see the Linux Network Administrators’ Guide for

more information, including a basic description of how networks operate.

Network logins

Network logins work a little differently than normal logins. There is a separate physical serial line for

each terminal via which it is possible to log in. For each person logging in via the network, there is a

separate virtual network connection, and there can be any number of these.

It is therefore not possible

to run a separate getty for each possible virtual connection. There are also several different ways to log

in via a network, telnet and rlogin being the major ones in TCP/IP networks.

Network logins have, instead of a herd of gettys, a single daemon per way of logging in (telnet and

rlogin have separate daemons) that listens for all incoming login attempts. When it notices one, it starts a

new instance of itself to handle that single attempt; the original instance continues to listen for other

attempts. The new instance works similarly to getty.

Network ﬁle systems

One of the more useful things that can be done with networking services is sharing ﬁles via a network ﬁle

system. The one usually used is called the Network File System, or NFS, developed by Sun.

With a network ﬁle system any ﬁle operations done by a program on one machine are sent over the

network to another computer. This fools the program to think that all the ﬁles on the other computer are

actually on the computer the program is running on. This makes information sharing extremely simple,

since it requires no modiﬁcations to programs.

Chapter 2. Overview of a Linux System

Mail

Electronic mail is usually the most important method for communicating via computer. An electronic

letter is stored in a ﬁle using a special format, and special mail programs are used to send and read the

letters.

Each user has an incoming mailbox (a ﬁle in the special format), where all new mail is stored. When

someone sends mail, the mail program locates the receiver’s mailbox and appends the letter to the

mailbox ﬁle. If the receiver’s mailbox is in another machine, the letter is sent to the other machine, which

delivers it to the mailbox as it best sees ﬁt.

The mail system consists of many programs. The delivery of mail to local or remote mailboxes is done

by one program (the mail transfer agent or MTA, e.g., sendmail or smail), while the programs users use

are many and varied (mail user agent or MUA, e.g., pine or elm). The mailboxes are usually stored in

/var/spool/mail.

Printing

Only one person can use a printer at one time, but it is uneconomical not to share printers between users.

The printer is therefore managed by software that implements a print queue: all print jobs are put into a

queue and whenever the printer is done with one job, the next one is sent to it automatically. This relieves

the users from organizing the print queue and ﬁghting over control of the printer.

The print queue software also spools the printouts on disk, i.e., the text is kept in a ﬁle while the job is in

the queue. This allows an application program to spit out the print jobs quickly to the print queue

software; the application does not have to wait until the job is actually printed to continue. This is really

convenient, since it allows one to print out one version, and not have to wait for it to be printed before

one can make a completely revised new version.

The ﬁlesystem layout

The ﬁlesystem is divided into many parts; usually along the lines of a root ﬁlesystem with /bin, /lib,

/etc, /dev, and a few others; a /usr ﬁlesystem with programs and unchanging data; a /var ﬁlesystem

with changing data (such as log ﬁles); and a /home ﬁlesystem for everyone’s personal ﬁles. Depending

on the hardware conﬁguration and the decisions of the system administrator, the division can be

different; it can even be all in one ﬁlesystem.

Chapter 3 describes the ﬁlesystem layout in some detail; the Linux Filesystem Standard covers it in

somewhat more detail.

Chapter 3. Overview of the Directory Tree

“ Two days later, there was Pooh, sitting on his branch, dangling his legs, and there, beside him, were four pots

of honey...” (A.A. Milne)

This chapter describes the important parts of a standard Linux directory tree, based on the FSSTND

ﬁlesystem standard. It outlines the normal way of breaking the directory tree into separate ﬁlesystems

with different purposes and gives the motivation behind this particular split. Some alternative ways of

splitting are also described.

Background

This chapter is loosely based on the Linux ﬁlesystem standard, FSSTND, version 1.2 (see the

bibliography), which attempts to set a standard for how the directory tree in a Linux system is organized.

Such a standard has the advantage that it will be easier to write or port software for Linux, and to

administer Linux machines, since everything will be in their usual places. There is no authority behind

the standard that forces anyone to comply with it, but it has got the support of most, if not all, Linux

distributions. It is not a good idea to break with the FSSTND without very compelling reasons. The

FSSTND attempts to follow Unix tradition and current trends, making Linux systems familiar to those

with experience with other Unix systems, and vice versa.

This chapter is not as detailed as the FSSTND. A system administrator should also read the FSSTND for

a complete understanding.

This chapter does not explain all ﬁles in detail. The intention is not to describe every ﬁle, but to give an

overview of the system from a ﬁlesystem point of view. Further information on each ﬁle is available

elsewhere in this manual or the manual pages.

The full directory tree is intended to be breakable into smaller parts, each on its own disk or partition, to

accomodate to disk size limits and to ease backup and other system administration. The major parts are

the root, /usr, /var, and /home ﬁlesystems (see Figure 3-1). Each part has a different purpose. The

directory tree has been designed so that it works well in a network of Linux machines which may share

some parts of the ﬁlesystems over a read-only device (e.g., a CD-ROM), or over the network with NFS.

Chapter 3. Overview of the Directory Tree

Figure 3-1. Parts of a Unix directory tree. Dashed lines indicate partition limits.

home devbin proc lib etc varusr boot

ftp liw linus log tmprunlib spoolbin lib man tmp

The roles of the different parts of the directory tree are described below.

• The root ﬁlesystem is speciﬁc for each machine (it is generally stored on a local disk, although it could

be a ramdisk or network drive as well) and contains the ﬁles that are necessary for booting the system

up, and to bring it up to such a state that the other ﬁlesystems may be mounted. The contents of the

root ﬁlesystem will therefore be sufﬁcient for the single user state. It will also contain tools for ﬁxing a

broken system, and for recovering lost ﬁles from backups.

• The /usr ﬁlesystem contains all commands, libraries, manual pages, and other unchanging ﬁles

needed during normal operation. No ﬁles in /usr should be speciﬁc for any given machine, nor

should they be modiﬁed during normal use. This allows the ﬁles to be shared over the network, which

can be cost-effective since it saves disk space (there can easily be hundreds of megabytes in /usr),

and can make administration easier (only the master /usr needs to be changed when updating an

application, not each machine separately). Even if the ﬁlesystem is on a local disk, it could be

mounted read-only, to lessen the chance of ﬁlesystem corruption during a crash.

• The /var ﬁlesystem contains ﬁles that change, such as spool directories (for mail, news, printers, etc),

log ﬁles, formatted manual pages, and temporary ﬁles. Traditionally everything in /var has been

somewhere below /usr, but that made it impossible to mount /usr read-only.

• The /home ﬁlesystem contains the users’ home directories, i.e., all the real data on the system.

Separating home directories to their own directory tree or ﬁlesystem makes backups easier; the other

parts often do not have to be backed up, or at least not as often (they seldom change). A big /home

might have to be broken on several ﬁlesystems, which requires adding an extra naming level below

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