The document provides an overview of the Linux operating system, including: - An introduction to Linux and its history as an open-source clone of UNIX. - Descriptions of Linux's core functionality like multi-user support and virtual memory. - Discussions of key Linux components like kernels, distributions, packages, and updates. - Explanations of enterprise-level Linux features around performance, scalability, and reliability.

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Linux操作系统
简介
周炯
上海艾基信息技术有限公司

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内容提要
• Linux简介
• Linux的安装
• SHELL及常用程序
• 文件编辑器vi
• 目录和文件管理
• 文件系统管理
• 用户管理
• 网络管理
• 网络文件系统
• 模块安装和配置
• 系统管理
• 系统优化
• 开发工具
• Internet管理

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Linux——简介
• Linux操作系统是可以运行在许多不同类型的计
算机上的一种操作系统的“内核”。它是提供命
令行或者程序与计算机硬件之间接口的软件的核
心部分。Linux操作系统内核管理以下事情：比
如内存、采用什么方法以及在什么时候打开或者
关闭文件、哪一个进程或者程序可以获得计算机
的中央处理单元(CPU)等等。
• Linux操作系统可以说是UNIX操作系统的一个克
隆体，它最初是在1991年10月5日由它的作者
Linus Torvalds于赫尔辛基大学发布的。

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Linux功能
• 所有主要的网络协议
• 硬盘配额支持
• 全部的源代码
• 国际化的字体和键盘
• 作业控制
• 数学协处理器仿真
• 内存保护
• 多平台
• 多处理器
• 多用户
• 多任务
• 共享的库文件
• 支持多种文件系统
• 虚拟控制台
• 虚拟内存
• 其他更多功能

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GPL和Free
• Linux操作系统遵从GNU公共许可证
（ GNU Public License，简称GPL）的规
定。
• Linux对外的一个重要的特点就是”Free”，
自由和免费。

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What is Linux?
• Linux is an operating system with the
following attributes:
– Multi-user
– Multi-tasking
– Virtual memory system
– X-Windows
– Compatible with the IEEE POSIX.1
standard
– Non-proprietary source code
– Source code is available

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Is Linux the same as UNIX?
• The command set is similar
• They work the same
• They look the same
• Linux cannot use the UNIX
trademark
• Linux is essentially UNIX

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Is Linux a real OS?
• Yes, absolutely
• Linux is used
– In mission critical applications
– Around the world
• There are many flavors of Linux
available
– We call them: Distributions

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Linux发行版本的概念
• 大多数的Linux操作系统的发行版本都使用标准
的Linux内核，但有时候也会稍微加以修改，这
个操作系统现在的规模已经变得相当庞大了，因
此许多人更愿意购买一张它的CD-ROM光盘。每
一种发行版本彼此之间都稍微有一些差异，这些
差异主要表现在它们各自的安装程序包上，还表
现在安全性与可用性等方面侧重点的不同。把系
统内核、附带的工具程序及应用软件包等等打包
在一起，这样组成的一个Linux操作系统的集合
体就是我们说的某一种发行版本。

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谁使用Linux操作系统
• Linux正在逐渐赢得普通用户的青睐。但是它仍
然不是一个适用于普通大众的操作系统。对那些
习惯了当今鼠标界面操作系统的人们来说， 学习
仍是很困难的。需要学习一大套从未接触过的命
令，还需要学习与长期形成的概念不相同的那些
对待与处理事情的方法。对那些具有UNIX操作系
统使用经验的人们来说，Linux可是容易多了。
• 专业用户、系统管理员和计算机开发人员通常都
会比一般的用户更容易掌握Linux操作系统。但
就是对这些人来说，这方面的学习与实践也需要
有足够的耐心与专心。

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Enterprise vs. Retail
• Retail distributions
– Faster release cycles (4-6 months)
– Geared for home/productivity users
– Shorter support lifetimes
– Examples: RHL9, SuSE Linux 9
• Enterprise level distributions
– Slower release cycles (12-18 months)
– Longer support lifetimes (3-5 years)
– Examples: RHEL3/4, SLES9
– Adds performance and scalability
enhancements

12. Linux Distribution Overview
• The core parts of a Linux system are:
– Linux kernel
– User space utilities and applications
• The kernel and user space programs
together make up the complete
operating system

13. Linux Kernel
• Core component of the operating
system
– Configurable and tunable
– Provides main OS functions
• I/O, disk, network, etc.
• CPU Scheduling
• Memory management
• uname -r shows the kernel version
number:# uname -r
2.4.9-e.25

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Kernel concepts
• Linux is based on a modular non-
microkernel architecture
– All device drivers share the same
memory with the kernel
– Device drivers are modular and can be
loaded/unloaded dynamically
• Linux is multi-tasking
• Linux is a virtual-memory OS
• Most kernel parameters can be
modified on the fly

15. • All components of the operating
system are delivered via RPM
packages
– Kernel
– System utilities
– Applications
• Both Red Hat and SLES8
distributions use the RPM Package
Manager (RPM)
– Originally named “Red Hat Package
Manager”
Software Packages

16. Linux Updates
• Apply the recommended updates by
the distribution vendor:
– Most vendors provide automatic updates
• Red Hat Network supplies updates
automatically
– up2date
• SuSE uses
– YaST2 (Yet Another Setup Tool 2)
– you (YaST Online Update)

17. Linux Enterprise Features
• Linux enterprise features support :
– Performance
– Scalability
– Reliability

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Symmetric Multiprocessing
• Fully multiprocessor capable (SMP)
– RHEL3: 16 processors
– SLES8: 32 processors
– Uniprocessor configuration supported on
both
• Intel Hyperthreading (HT) enabled
on IA-32
– Physical-to-logical CPU affinity
scheduling

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Improved Memory Utilization
• Use more than 4GB of RAM on IA-32
– RHEL 2.1: max 16GB supported
– RHEL3: max 64GB supported
– SLES8: up to 64GB supported
– Some older drivers not capable of accessing
more than 4GB of RAM
• May perform “bounce buffering” to compensate
• Usually not a concern for enterprise-class drivers
• Kernel memory used more efficiently than
before
• Run more processes without swapping

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Virtual Memory
• Each process has a private address space
– Keeps private data in memory secure
– Prevents inter-process data corruption
– Contiguous view of memory
• Demand-based paging
– Pages are “swapped” out when low on RAM
– Pages are “swapped” in when accessed again
• Allows the system to use more memory
than any single space can address

21. Virtual Filesystem (VFS)
• Linux supports multiple file systems
– OS is file system independent
– Multiple file systems can be used
simultaneously
• Cross-platform compatibility
• Performance
• VFS provides a single filesystem
interface

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Filesystems
• Important ones to know:
– ext2/3 - Red Hat default (ext3)
– reiserfs - SLES8 default
– NFS - Network Filesystem
– Procfs - kernel virtual filesystem
– ISO 9660 (CD-ROM)
– OCFS - Oracle Cluster Filesystem
• ext2/3 and reiserfs are the most common
• Use OCFS instead of raw devices in RAC

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Filesystem Cache
• Buffers all filesystem I/O
– All filesystem I/O is copied to/from cache
buffers
– By default, writes are not immediately flushed
• Hardware I/O is deferred
– Reads benefit from previous accesses as well
as automatic read-ahead
• May not need to perform a real hardware I/O
• Made up of page cache and buffer cache
– Page cache tends to be more heavily used
• Reduced automatically when low on RAM

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Process Disk file
Write
Read
Raw Devices
• Have traditionally been considered the
high performance solution
– Bypasses the filesystem buffer cache
– Moves larger buffers than file system I/Os
• Requires more experienced administration

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Modular Drivers
• Loadable kernel modules (LKM)
• Can be unloaded/reloaded without
rebooting
• Modules provide:
– Device drivers
– File system drivers
– System calls
– Network drivers
– Executable interpreters
– Terminal device (TTY) drivers

26. I/O Modes
• Disk I/O can be performed in several
different modes
– Asynchronous vs. synchronous
– Direct vs. buffered
Process Buffer cache Disk file
Write Flush

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Storage Infrastructure
• Direct-attached storage (DAS)
– IDE, SCSI
– e.g., LSI Megaraid
• Network-Attached Storage (NAS)
– NFS
– e.g., Network Appliance Filer
• Storage Area Networks (SAN)
– FibreChannel
– e.g., EMC Clariion

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Linux Clusters
• Scalable Shared Storage
– SCSI, SAN (FibreChannel), Firewire
(devel.)
• Must use raw devices or OCFS
– Network Attached Storage (NFS)
– LVM and software RAID (“md”) not
cluster-aware
• Linux includes cluster management
software

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Linux Kernel Enhancements
• Performance
– Asynchronous I/O
– Eliminate kernel locks
– Large SGA: > 4 GB
– Support more Oracle users
• Stability
– Graceful degradation under load
• Manageability
– (Remote) Crash Dump Facility
– Configuration scripts

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Summary
• Linux is
– An open-source fully featured operating
system
– Being adopted in the enterprise arena
today

31. Q U E S T I O N S
A N S W E R S