Chapter 6

1. Troubleshooting the Operating System Part 2 Chapter 6

2. LILO Boot Errors

3. Error Codes • The LILO boot loader is the first piece of code that takes control of the boot process form the BIOS. It loads the Linux kernel, and then passes control entirely to the Linux kernel. • When there is a problem with LILO an error code will be displayed: • None, L, LI, LI101010… LIL , LIL?, LIL-, LILO • Each error code indicates a problem. • If there is no error code then this means that LILO has not loaded. • L means the second stage of LILO did not load.

4. Booting a Linux System without LILO • There are few options which can be used to boot the computer: • LOADLIN: a DOS utility that can be used to boot Linux. • LILO on a Floppy • Using the LILO on a Floppy method is the least useful but it can help in some instances. • From this screen during installation, a LILO boot floppy disk can be created which can be used to boot Linux from LILO using the floppy disk.

5. Emergency Boot System • Linux provides an emergency system’s copy of LILO, which can be used to boot Linux in the event that the original LILO boot loader has errors or is not working. • This is known as the Emergency Boot System. • To use this copy of LILO configuration changes must be made in lilo.conf.

6. Using an Emergency Boot Disk in Linux • The emergency boot disk should have the necessary disk utilities such as fdisk, mkfs, and fsck, which can be used to format a hard drive so that Linux can be installed on it. • The simplest and most recommended method for creating a custom emergency boot disk to suit the needs of an individual computer system is to modify one of the existing boot disks.

7. Using an Emergency Boot Disk in Linux • It is always important to include some sort of backup software utility. • If a change or repair to some configuration files needs to be made, first back them up. • Most distributions come with some sort of backup utility like tar, restore, cpio, and possibly others. • Using the tar –t command will lists the contents of an archive.

8. Recognizing Common Errors

9. Various Reasons for Package Dependency Problems • When a package is installed in a Linux system there might be other packages that need to be installed for that particular package to work properly. • The dependency package may have certain files which need to be in place or it may run certain services which need to be started before the package that is to be installed can work. • Linux will often notify the user if they are installing a package that has dependencies so that they can be installed as well.

10. Solutions to Package Dependency Problems • One solution to solving package dependency problems is to simply ignore the error message and forcibly install the package anyway. • The correct and recommended solution is to modify the system so that it has the necessary dependencies that are needed to run properly. • It may be necessary to rebuild the package from source code if there are dependency error messages showing up. • The easiest way is to locate a different version of the package that is causing the problems. • Another option is to look for a newer version of the package.

11. Backup and Restore Errors • Backup and Restore errors can occur at different points. • Some errors will occur when the system is actually performing the backup. • Other errors will occur during the restore process when the system is attempting to recover data. • Some of the most common types of problems: • Driver problems -Tape drive access errors • File access errors - Media errors • Files not found errors • To access the backup devices use these files: /dev/ht0 and /dev/nst0.

12. Application Failure on Linux Servers • There are several things that can provide some indication of an application failure or software problem on a Linux server: • Failure to Start • Failure to Respond • Slow Responses • Unexpected Reponses • Crashing Application or Server • A good general rule is to check the system’s logs. • The system’s log files are usually the place to find most error messages that are generated because they are not always displayed on the screen.

13. Troubleshooting Network Problems

14. Operator Error • Be sure that users are using the correct username and password and that their accounts are not restricted in a way that prevents them from being able to connect to the network. • Software settings might have been changed by the installation routine of a recently installed program, or the user might have been experimenting with settings. • Users accidentally, or purposely, delete files, and power surges or shutting down the computer abruptly can damage file data. • Viruses can also damage system files or user data.

15. Using TCP/IP Utilities • The first step in checking for a suspected connectivity problem is to ping the host. • If a reply is received, the physical connection between the two computers is intact and working. • The successful reply also signifies that the calling system can reach the Internet. • The term ping time refers to the amount of time that elapses between the sending of the Echo Request and receipt of the Echo Reply. • A low ping time indicates a fast connection.

16. Using TCP/IP Utilities • The loop back address 127.0.0.1 can be ping to verify that TCP/IP is installed correctly. • Tracing utilities are used to discover the route taken by a packet to reach its destination. • The way to determine packet routing in UNIX systems is the traceroute command. • Tracerouteshows all the routers through which the packet passes as it travels through the network from sending computer to destination computer. • This is useful for determining at what point connectivity is lost or slowed. • The netstat command is used to show information about the active connections, routing tables and interfaces.