Linux.com Article DB: Bootstrapping a Linux system - An Analysis

The start_kernel( ) function. What does it do?

The start_kernel( ) function completes the "initialization" of the Linux Kernel. All the essential Kernel components are initialized when this function executes. This is the last step of the entire "bootstrapping" process.

The following takes place when this function executes:

The paging_init( ) function is executed that initializes the Page Tables.
The mem_init( ) function is executed that initializes the Page Descriptors.
The trap_init( ) and init_IRQ( ) functions are executed that initializes the IDT for the final time.
The kmem_cache_init( ) and kmem_cache_sizes_init ( ) functions are executed that initializes the Slab Allocator.
The time_init( ) function is executed that initializes the System Date & Time.
The Kernel thread for process 1 is created by invoking the kernel_thread( ) function. This in turn creates the other kernel threads and executes /sbin/init program.

The "Linux version 2.4.2 ..." message is displayed right after the beginning of start_kernel( ). Many other messages are displayed also. At the very end, the very familiar login prompt appears on the console. This tells the user that the Linux Kernel is up and running, and just raring to go... and dominate the world!

Conclusion

This sums up our overview of the entire bootstrapping process of a Linux system. As the readers may rightly note I have not explained most of the other components and terms that I have used. A few include IDT, GDT, eip register, cs register and so on. The full explanation of all these terms would make it impossible to complete the article in just a few pages, and would make the entire topic rather boring to some people. In this article I provide everyone with just a glimpse of the processes and other various things that take place when a Linux system boots. In you want more in-depth coverage of all the associated functions like paging_init( ) and mem_init( ) go buy a book.

About the Author: My name is Subhasish Ghosh. I am 20, currently a computer-systems engineering student in India. I am a Microsoft Certified Professional (MCP), MCP certified on NT 4.0 and recently completed Red Hat Linux Certified Engineer (RHCE) Training. I have been working with Linux for a long time now, have programmed using C, C++, VC++, COM, MFC, DCOM, ATL 3.0, Perl, Python and Linux programming using GTK+. Currently I'm busy learning the Linux Kernel Architecture in detail, writing articles for Linux.com and most importantly practicing non-geek talk with my girlfriend, Hanna. E-mail: auspicious_blessingsindia@hotmail.com

PLEASE NOTE: I like hearing from and helping Linux users from all over the world. Anyone interested in e-mailing me should feel free to do so. However, I request computer-freaks, people who complain too much about everything and specifically egoistic Indians pretending to know everything trying to point out mistakes in my articles please do not e-mail me. I don't have much time for that. Thank you!

Originally Published: Thursday, 19 July 2001	Author: Subhasish Ghosh
Published to: learn_articles_firststep/General	Page: 6/6 - [Printable]
Bootstrapping a Linux system - An Analysis Ever wonder what happens between powering on your system and the logon prompt? You see all the screen messages, but what do they mean? Linux.com writer Subhasish Ghosh wondered the same thing, and went to find out in Bootstrapping a Linux System.

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The start_kernel( ) function. What does it do? The start_kernel( ) function completes the "initialization" of the Linux Kernel. All the essential Kernel components are initialized when this function executes. This is the last step of the entire "bootstrapping" process. The following takes place when this function executes: The paging_init( ) function is executed that initializes the Page Tables. The mem_init( ) function is executed that initializes the Page Descriptors. The trap_init( ) and init_IRQ( ) functions are executed that initializes the IDT for the final time. The kmem_cache_init( ) and kmem_cache_sizes_init ( ) functions are executed that initializes the Slab Allocator. The time_init( ) function is executed that initializes the System Date & Time. The Kernel thread for process 1 is created by invoking the kernel_thread( ) function. This in turn creates the other kernel threads and executes /sbin/init program. The "Linux version 2.4.2 ..." message is displayed right after the beginning of start_kernel( ). Many other messages are displayed also. At the very end, the very familiar login prompt appears on the console. This tells the user that the Linux Kernel is up and running, and just raring to go... and dominate the world! Conclusion This sums up our overview of the entire bootstrapping process of a Linux system. As the readers may rightly note I have not explained most of the other components and terms that I have used. A few include IDT, GDT, eip register, cs register and so on. The full explanation of all these terms would make it impossible to complete the article in just a few pages, and would make the entire topic rather boring to some people. In this article I provide everyone with just a glimpse of the processes and other various things that take place when a Linux system boots. In you want more in-depth coverage of all the associated functions like paging_init( ) and mem_init( ) go buy a book. About the Author: My name is Subhasish Ghosh. I am 20, currently a computer-systems engineering student in India. I am a Microsoft Certified Professional (MCP), MCP certified on NT 4.0 and recently completed Red Hat Linux Certified Engineer (RHCE) Training. I have been working with Linux for a long time now, have programmed using C, C++, VC++, COM, MFC, DCOM, ATL 3.0, Perl, Python and Linux programming using GTK+. Currently I'm busy learning the Linux Kernel Architecture in detail, writing articles for Linux.com and most importantly practicing non-geek talk with my girlfriend, Hanna. E-mail: auspicious_blessingsindia@hotmail.com PLEASE NOTE: I like hearing from and helping Linux users from all over the world. Anyone interested in e-mailing me should feel free to do so. However, I request computer-freaks, people who complain too much about everything and specifically egoistic Indians pretending to know everything trying to point out mistakes in my articles please do not e-mail me. I don't have much time for that. Thank you!
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