Table of Contents for
Learning Linux Shell Scripting

Version ebook / Retour

Cover image for bash Cookbook, 2nd Edition Learning Linux Shell Scripting by Ganesh Sanjiv Naik Published by Packt Publishing, 2015
  1. Cover
  2. Table of Contents
  3. Learning Linux Shell Scripting
  4. Learning Linux Shell Scripting
  5. Credits
  6. About the Author
  7. Acknowledgments
  8. About the Reviewers
  9. www.PacktPub.com
  10. Preface
  11. What you need for this book
  12. Who this book is for
  13. Conventions
  14. Reader feedback
  15. Customer support
  16. 1. Getting Started and Working with Shell Scripting
  17. Tasks done by shell
  18. Working in shell
  19. Learning basic Linux commands
  20. Our first script – Hello World
  21. Compiler and interpreter – difference in process
  22. When not to use scripts
  23. Various directories
  24. Working more effectively with shell – basic commands
  25. Working with permissions
  26. Summary
  27. 2. Drilling Deep into Process Management, Job Control, and Automation
  28. Monitoring processes using ps
  29. Process management
  30. Process monitoring tools – top, iostat, and vmstat
  31. Understanding "at"
  32. Understanding "crontab"
  33. Summary
  34. 3. Using Text Processing and Filters in Your Scripts
  35. IO redirection
  36. Pattern matching with the vi editor
  37. Pattern searching using grep
  38. Summary
  39. 4. Working with Commands
  40. Command substitution
  41. Command separators
  42. Logical operators
  43. Pipes
  44. Summary
  45. 5. Exploring Expressions and Variables
  46. Working with environment variables
  47. Working with read-only variables
  48. Working with command line arguments (special variables, set and shift, getopt)
  49. Understanding getopts
  50. Understanding default parameters
  51. Working with arrays
  52. Summary
  53. 6. Neat Tricks with Shell Scripting
  54. The here document and the << operator
  55. The here string and the <<< operator
  56. File handling
  57. Debugging
  58. Summary
  59. 7. Performing Arithmetic Operations in Shell Scripts
  60. Using the let command for arithmetic
  61. Using the expr command for arithmetic
  62. Binary, octal, and hex arithmetic operations
  63. A floating-point arithmetic
  64. Summary
  65. 8. Automating Decision Making in Scripts
  66. Understanding the test command
  67. Conditional constructs – if else
  68. Switching case
  69. Implementing simple menus with select
  70. Looping with the for command
  71. Exiting from the current loop iteration with the continue command
  72. Exiting from a loop with a break
  73. Working with the do while loop
  74. Using until
  75. Piping the output of a loop to a Linux command
  76. Running loops in the background
  77. The IFS and loops
  78. Summary
  79. 9. Working with Functions
  80. Passing arguments or parameters to functions
  81. Sharing the data by many functions
  82. Declaring local variables in functions
  83. Returning information from functions
  84. Running functions in the background
  85. Creating a library of functions
  86. Summary
  87. 10. Using Advanced Functionality in Scripts
  88. Using the trap command
  89. Ignoring signals
  90. Using traps in function
  91. Running scripts or processes even if the user logs out
  92. Creating dialog boxes with the dialog utility
  93. Summary
  94. 11. System Startup and Customizing a Linux System
  95. User initialization scripts
  96. Summary
  97. 12. Pattern Matching and Regular Expressions with sed and awk
  98. sed – noninteractive stream editor
  99. Using awk
  100. Summary
  101. Index

Process monitoring tools – top, iostat, and vmstat

We can view the native performance of various processes in OS using tools which will be discussed further. To view a dynamic real-time view of the top running processes in OS, use the following command:

$top
Process monitoring tools – top, iostat, and vmstat

An explanation of the top command generated output is as follows:

The $top command displays a lot of information about the running system.

The first line of the display is shown as follows:

Process monitoring tools – top, iostat, and vmstat

The description of fields in the first line is as follows:

  • Current time
  • System uptime
  • Number of users logged in
  • Load average of 5, 10, and 15 minutes, respectively

The second line is shown as follows:

Process monitoring tools – top, iostat, and vmstat

This line shows the summary of tasks or processes. It shows the total number of all the processes, which includes the total number of running, sleeping, stopped, and zombie processes.

The third line is shown as follows:

Process monitoring tools – top, iostat, and vmstat

This line shows information about CPU usage in % in different modes as follows:

  • * us (user): CPU usage in % for running (un-niced) the user processes
  • * sy (system): CPU usage in % for running the kernel processes
  • * ni (niced): CPU usage in % for running the niced user processes
  • * wa (IO wait): CPU usage in % for waiting for the IO completion
  • * hi (hardware interrupts): CPU usage in % for serving hardware interrupts
  • * si (software interrupts): CPU usage in % for serving software interrupts
  • * st (time stolen): CPU usage in % for time stolen for this vm by the hypervisor

The fourth line is shown as follows:

Process monitoring tools – top, iostat, and vmstat

This line provides information about memory usage. It shows the physical memory that is used, free, available, and used for buffers. The next line shows the swap memory that is available, used, free, and cached.

After this line, we see the table of values with the following columns:

  • PID: This is the ID of the process
  • USER: This is the user that is the owner of the process
  • PR: This is the priority of the process
  • NI: This is the "NICE" value of the process
  • VIRT: This is the virtual memory used by the process
  • RES: This is the physical memory used for the process
  • SHR: This is the shared memory of the process
  • S: This indicates the status of the process: S=sleep, R=running, and Z=zombie (S)
  • %CPU: This is the % of CPU used by this process
  • %MEM: This is the % of RAM used by the process
  • TIME+: This is the total time of activity of this process
  • COMMAND: This is the name of the process

Let's take a look at the performance monitoring tools—iostat, vmstat, and sar:

  • To view the statistics of the CPU and the input/output device's utilization, use the following command:
    $ iostat
    Process monitoring tools – top, iostat, and vmstat
    $ iostat –c

    Shows only CPU statistics

    $ iostat –d

    Shows only disk statistics

  • To view the virtual memory statistics, use the following command:
    $vmstat
    Process monitoring tools – top, iostat, and vmstat
    $ vmstat  -s

    This shows various event counters and memory statistics.

    $ vmstat –t 1 5

    Runs for every one second stops after executing for five intervals.

    $ sar –u 2 3

    This will show the CPU activity report every 2 seconds, 3 times:

    Process monitoring tools – top, iostat, and vmstat