1. Troubleshooting and Performance
Chapter Fourteen
Troubleshooting and Performance

2. Objectives Describe and outline common troubleshooting procedures
Identify good troubleshooting practices
Effectively troubleshoot common hardware-related problems
Effectively troubleshoot common software-related problems
Monitor system performance using command-line and graphical utilities
Understand the purpose and usage of kernel modules

3. Troubleshooting Methodology
Figure 14-1: The maintenance cycle

4. Troubleshooting Methodology
Monitoring
Process by which system areas are observed for problems or irregularities
Proactive maintenance
Measure taken to reduce future system problems
Reactive maintenance
Measure taken when system problems arise

5. Troubleshooting Methodology
Documentation
System information that is stored in a log book for future references
Troubleshooting procedures
The tasks performed when solving system problems

6. Troubleshooting Methodology
Figure 14-2: Common troubleshooting procedures

7. Troubleshooting Methodology
Two golden rules to guide you during any troubleshooting process:
Prioritize problems
Prioritize the problems according to severity and spend a reasonable amount of time on each problem given its priority
Try to solve the root of the problem
To avoid missing the underlying cause of any problem, try to justify why a certain solution is successful

8. Hardware-Related Problems
Figure 14-3: The KDE Control Center

9. Hardware-Related Problems
The absence of a device driver will also prevent the operating system from using the associated hardware devices
Kudzu program
Program used to detect and install support for new hardware

10. Hardware-Related Problems
Figure 14-4: The kudzu welcome screen

11. Hardware-Related Problems
Figure 14-5: Configuring new hardware using kudzu

12. Hardware-Related Problems
If the hard disk that contains the / filesystem fails, then perform the following steps:
Power down the computer and replace the failed hard disk
Reinstall Linux on the new hard disk
Restore the original configuration and data files using a back-up utility

13. Software-Related Problems: Application-Related Problems
Dependencies
The prerequisites required for program execution such as shared libraries or other packages
ldd command
Command used to display the shared libraries used by a certain program

14. Software-Related Problems: Application-Related Problems
ldconfig command
Command that updates the /etc/ld.so.conf and /etc/ld.so.cache files
/etc/ld.so.conf files
File that contains a list of directories that contain shared libraries
/etc/ld.so.cache file
File that contains the location of shared library files

15. Software-Related Problems: Application-Related Problems
Filehandles
Connection that a program makes to files on a filesystem
unlimit command
Command used to modify process limit parameters in the current shell
/var/log directory
Directory that contains most system log files

16. Software-Related Problems: OS-Related Problems
Most software-related problems are related to the operating system itself
These typically involve problems with boot loaders, filesystems, and serial devices
mkbootdisk command
Command used to create a boot floppy diskette

17. Software-Related Problems: OS-Related Problems
Figure 14-6: The Red Hat Linux installation welcome screen

18. Software-Related Problems: OS-Related Problems
Figure 14-7: Obtaining a shell in rescue mode

19. Software-Related Problems: OS-Related Problems
Figure 14-8: The command-line shell used in rescue mode

20. Software-Related Problems: OS-Related Problems
Table 14-1: Common keywords used with the setserial utility

21. Performance Monitoring
Jabbering
Process by which failing hardware components send large amounts of information to the CPU
Bus mastering
Process by which peripheral components perform tasks normally executed by the CPU

22. Performance Monitoring
To ease identification of performance problems, you should run performance utilities on a healthy Linux system on a regular basis during normal business hours and record results in a system log book
Baseline
A measure of normal system activity

23. Monitoring Performance with sysstat Utilities
System Statistics (sysstat) package
Software package that contains common performance monitoring utilities such as mpstat, iostat, sar, and isag
Multiple Processor Statistics (mpstat) utility
Command that displays CPU statistics

24. Monitoring Performance with sysstat Utilities
Input/Output Statistics (iostat) command
Command that displays Input/Output statistics for block devices
System Activity Reporter (sar) command
Command that displays various system statistics

25. Monitoring Performance with sysstat Utilities
Table 14-2: Common options to the sar command

26. Monitoring Performance with sysstat Utilities
Table 14-2 (continued): Common options to the sar command

27. Monitoring Performance with sysstat Utilities
If there are a large number of pages being sent to and taken from the swap partition, then the system will suffer from slower performance
To remedy this, you could add more physical memory (RAM) to the system
Interactive System Activity Grapher (isag) command
Command used to graph system performance information stored in the /var/log/sa directory

28. Monitoring Performance with sysstat Utilities
Figure 14-9: Choosing a file to view using the System Activity Grapher

29. Monitoring Performance with sysstat Utilities
Figure 14-10: Choosing statistics using the System Activity Grapher

30. Monitoring Performance with sysstat Utilities
Figure 14-11: Viewing user statistics using the System Activity Grapher

31. Other Performance Monitoring Utilities
free command
Command used to display memory and swap statistics
vmstat command
Command used to display memory, CPU, and swap statistics

32. Kernel Modules
Many device drivers and kernel features are compiled into the kernel
However, these may also be inserted into the kernel as modules to reduce the size of the kernel
It is good form to compile standard device support into the kernel and leave support for other devices and features as modules

33. Kernel Modules insmod command modprobe command lsmod command
Command used to insert a module into the Linux kernel
modprobe command
Command used to insert a module and all necessary prerequisites modules into the Linux kernel
lsmod command
Command that lists modules currently used by the Linux kernel

34. Kernel Modules rmmod command /etc/modules.conf file
Command that removes a module from the Linux kernel
/etc/modules.conf file
File used to load and alias modules at system initialization
/etc/rc.d/rc.local file
File used to load modules at system initialization

35. Compiling a New Linux Kernel
To gain certain hardware or kernel support, it may be necessary to recompile the current kernel with different features or download the source code for a newer kernel and compile it
/usr/src/linux
The directory that contains source code for the Linux kernel during compilation

36. Compiling a New Linux Kernel
Figure 14-12: The make menuconfig interface

37. Compiling a New Linux Kernel
Figure 14-13: The make xconfig interface

38. Compiling a New Linux Kernel
Figure 14-14: Configuring code maturity level options

39. Compiling a New Linux Kernel
Figure 14-15: Configuring USB support

40. Patching the Linux Kernel
To install a more current Linux kernel version, you normally download the source code for that kernel and place it in a directory that will be referenced by /usr/src/linux
Patch command
Command used to supply a patch to the Linux kernel source code

41. Chapter Summary
After installation, Linux administrators monitor the system, perform proactive and reactive maintenance, and document important system information
Common troubleshooting procedures involve collecting data to isolate and determine the cause of system problems, as well as implementing and testing solutions that can be documented for future use
System problems may be categorized as hardware- or software-related

42. Chapter Summary
IRQ conflicts, invalid hardware settings, absence of kernel support, and hard disk failure are common hardware-related problems on Linux systems
Software-related system problems may be further categorized as application-related or operating system-related
System performance is affected by a variety of hardware and software factors

43. Chapter Summary
Using performance monitoring utilities to create a baseline is helpful when diagnosing performance problems in the future
System features and hardware support may be compiled into the Linux kernel or provided by a kernel module
You may compile a Linux kernel with only the necessary features and support in order to increase system performance