Linux 操作系统简介

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Linux 操作系统简介周炯周炯

上海艾基信息技术有限公司上海艾基信息技术有限公司


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


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。


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


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。


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


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


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


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。


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。


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

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

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 -r2.4.9-e.25


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

• 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

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)

Linux Enterprise Features• Linux enterprise features support :

– Performance– Scalability– Reliability


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


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


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

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


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


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


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


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

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


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


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


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


Summary• Linux is

– An open-source fully featured operating system

– Being adopted in the enterprise arena today

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Linux 操作系统 简介

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Linux 操作系统简介