1. Guide to Linux Installation and Administration, 2e 1 Chapter 9 Preparing for Emergencies

2. Guide to Linux Installation and Administration, 2e 2 Objectives In this chapter, you will: Understand your system’s vulnerabilities and plan to protect data and ensure minimum downtime Manage the power supply to your Linux computer Check the integrity of your Linux file systems Understand how redundant disk systems can protect data

3. Guide to Linux Installation and Administration, 2e 3 Understanding a System’s Vulnerabilities Computers continue to break down System administrators handle crises System administrators outline policies and procedures for emergencies

4. Guide to Linux Installation and Administration, 2e 4 Creating a Disaster Plan A disaster plan describes how an organization will respond to various threats to its information systems A disaster plan is based on an evaluation of different risk levels and the value of having systems up and their data available A disaster plan includes: –Information about your computer systems –Immediate steps that you will take to reduce their vulnerability –Steps required to get them running again when various problems occur

5. Guide to Linux Installation and Administration, 2e 5 Preventing Downtime Downtime — Occasions when an organization’s computer systems cannot respond to requests for information To prevent downtime: –Remove single points of failure –Make vulnerable components redundant

6. Guide to Linux Installation and Administration, 2e 6 Understanding High Availability Fault-tolerant computer systems that run continuously provide high availability High availability systems use special hardware and software to improve statistical uptime (up to 99.999%) A high availability cluster uses a resource group to handle computing tasks

7. Guide to Linux Installation and Administration, 2e 7 Creating Rescue Disks A rescue disk is a floppy disk that you can use to boot a Linux-based computer A boot disk lets you start your Linux system when the hard disk or boot manager has been damaged

8. Guide to Linux Installation and Administration, 2e 8 Maintaining Software Masters Software masters are original copies of an application supplied by software vendors Software masters and manuals should be carefully stored and maintained to allow recovery after a disaster

9. Guide to Linux Installation and Administration, 2e 9 Managing the Computer’s Power Supply The power supply converts the AC power from a wall socket to the low-voltage DC power used by computer chips, disk drives, and other peripherals For occasions when the power supply does fail –Keep a second power supply –Purchase a server with a built-in backup power supply

10. Guide to Linux Installation and Administration, 2e 10 A Computer’s Power Supply

11. Guide to Linux Installation and Administration, 2e 11 Providing Consistent Power to a Linux System Surge suppressors protect the computer’s power supply by removing the voltage spikes and minor power irregularities When the power actually fails, an uninterruptible power supply (UPS) is needed

12. Guide to Linux Installation and Administration, 2e 12 A Surge Suppressor Removes Voltage Spikes

13. Guide to Linux Installation and Administration, 2e 13 A Computer Connected to a UPS

14. Guide to Linux Installation and Administration, 2e 14 Automating Linux Shutdown A UPS allows time for a system administrator to shut down a Linux system gracefully UPS devices have a serial communications port that signals the Linux system in the event of a power outage In response, the Linux system executes simple scripts to determine what actions to take

15. Guide to Linux Installation and Administration, 2e 15 Events Tracked by a UPS Device via a Serial Port

16. Guide to Linux Installation and Administration, 2e 16 A Serial Connection between a UPS and a Linux System

17. Guide to Linux Installation and Administration, 2e 17 A Gnome-Based Graphical Interface to the Network UPS Tools Package

18. Guide to Linux Installation and Administration, 2e 18 Responding to a Power Outage Utilities that manage a UPS typically interact with the init program to send signals Init checks the /etc/inittab configuration file to determine what action to take All three signals cause to use the shutdown command: –shutdown –f –h +2 –shutdown -c –shutdown –h now

19. Guide to Linux Installation and Administration, 2e 19 Checking File System Integrity The fsck utility checks the integrity of a Linux file system Each Linux ext2 or ext3 file system includes a superblock where parameters about the file system are stored An inode contains parameters that describe each file in a file system. File records hold a file’s name and point to an inode Directory records are files that contain a list of filenames and corresponding inode numbers

20. Guide to Linux Installation and Administration, 2e 20 Checking File System Integrity A link allows two or more file records to refer to the same physical data stored in a file system A symbolic link is a file record that includes a path and filename, but not an inode number A hard link is a file record that includes a filename and inode, just like a regular file record

21. Guide to Linux Installation and Administration, 2e 21 Using the fsck Utility The fsck utility is run automatically at boot time to check all mounted file systems To force a complete check of a file system, use the fsck command with the –f option from a command line The fsck utility attempts to repair file system errors

22. Guide to Linux Installation and Administration, 2e 22 Hard and Symbolic Links in a Linux File System

23. Guide to Linux Installation and Administration, 2e 23 Defragmenting a File System All file systems are divided into units of storage called blocks Defragmenting is called disk optimization Defragmenting optimizes access time to files and reduces wear on the hard disk

24. Guide to Linux Installation and Administration, 2e 24 Tuning a Linux File System The dumpe2fs command provides information about the superblock and data blocks of a Linux ext2 or ext3 file system You can use the tune2fs utility both to read and to change file system parameters

25. Guide to Linux Installation and Administration, 2e 25 Understanding Redundant Disk Systems RAID (redundant arrays of inexpensive disks) — a storage technique using multiple inexpensive hard disks arranged in a predefined pattern (an array) to improve performance, increase fault tolerance, or both You can add RAID to your system using a separate hardware device

26. Guide to Linux Installation and Administration, 2e 26 Defining RAID Levels RAID levels differ in the amount of fault tolerance, the speed of reading or writing data, and the cost of implementation RAID levels include features: –Mirroring –Duplexing –Striping –Parity

27. Guide to Linux Installation and Administration, 2e 27 RAID-Linear RAID-Linear — A storage technique in which multiple physical devices are combined into a single logical device It does not provide any redundancy or fault tolerance, nor does it improve system performance

28. Guide to Linux Installation and Administration, 2e 28 RAID-Linear

29. Guide to Linux Installation and Administration, 2e 29 RAID-0 (Striping) RAID-0 — A RAID level that uses striping to improve disk performance without adding any fault tolerance A data storage technique, in which a single block of data is divided into pieces and stored on more than one hard disk, is called striping

30. Guide to Linux Installation and Administration, 2e 30 RAID-0, or Data Striping

31. Guide to Linux Installation and Administration, 2e 31 RAID-1 (Disk Mirroring and Duplexing) RAID-1 — A RAID level that uses disk mirroring to significantly improve fault tolerance and disk read performance Mirroring — a redundancy technique in which the contents of two file systems contain identical information Duplexing — a redundancy technique in which hard disks are accessed via different hard disk controllers

32. Guide to Linux Installation and Administration, 2e 32 RAID-3 (Striping with Parity) RAID-3 — A RAID level that uses striping with parity information to improve performance and increase fault tolerance Parity is a technique that allows corrupted data to be reconstructed using an extra piece of information that is created as the data is stored

33. Guide to Linux Installation and Administration, 2e 33 RAID-3, Striping with Parity

34. Guide to Linux Installation and Administration, 2e 34 RAID-5 (Striping and Parity) RAID-5 — A RAID level in which striping with parity is spread across all disks in the RAID array compared to RAID-3, in which the parity information is stored on a single hard disk Write caching — a feature of some storage systems in which information to be written to a RAID file system is stored in memory temporarily in order to improve the overall read/write performance of the file system

35. Guide to Linux Installation and Administration, 2e 35 RAID-5, Parity and Striping over Multiple Disks

36. Guide to Linux Installation and Administration, 2e 36 Using Hardware-Based RAID Hardware-based RAID — A RAID array that is contained in a separate hardware device (a RAID subsystem) and is controlled by a CPU and other components separate from the CPU of the Linux system Hot-swapping — Removing and replacing a failed hard drive or other component without turning off the power to the device

37. Guide to Linux Installation and Administration, 2e 37 Summary A disaster plan describes how an organization will respond to various threats to its information systems Fault tolerance is achieved by removing single points of failure and making vulnerable components redundant High availability systems use special hardware and software to improve statistical uptime Surge suppressors and UPS devices provide clean power to a computer system A UPS can inform a Linux system of power outages via a serial cable, while supplying power from its batteries until the system can be gracefully shut down

38. Guide to Linux Installation and Administration, 2e 38 Summary The fsck utility checks the integrity of a Linux file system at boot time or whenever the fsck utility is run from a command line Each Linux ext2 or ext3 file system includes a superblock where parameters about the file system are stored An inode contains parameters that describe each file in a file system, while file records hold a file’s name and point to an inode RAID systems let you improve speed, fault tolerance, or both, depending on the configuration you choose RAID levels include features such as mirroring, duplexing, striping, and parity