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.
5. Acegene IT Co. Ltd. 5
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。
6. Acegene IT Co. Ltd. 6
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
7. Acegene IT Co. Ltd. 7
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
8. Acegene IT Co. Ltd. 8
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
11. Acegene IT Co. Ltd. 11
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
14. Acegene IT Co. Ltd. 14
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)
18. Acegene IT Co. Ltd. 18
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
19. Acegene IT Co. Ltd. 19
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
20. Acegene IT Co. Ltd. 20
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
22. Acegene IT Co. Ltd. 22
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
23. Acegene IT Co. Ltd. 23
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
24. Acegene IT Co. Ltd. 24
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
25. Acegene IT Co. Ltd. 25
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
28. Acegene IT Co. Ltd. 28
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
29. Acegene IT Co. Ltd. 29
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
30. Acegene IT Co. Ltd. 32
Summary
• Linux is
– An open-source fully featured operating
system
– Being adopted in the enterprise arena
today