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Chapter Fourteen

Chapter Fourteen. Troubleshooting and Performance. Objectives. Describe and outline common troubleshooting procedures Identify good troubleshooting practices Effectively troubleshoot common hardware-related problems Effectively troubleshoot common software-related problems

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Chapter Fourteen

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  1. 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 • 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 • 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

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