kdb.md

The Kernel Debugger (kdb)

KDB is a text-based debugger included in the linux kernel intended for debugging kernel problems and analyzing system states. Kdb is useful for quickly examining the state of a system. To use kdb, the Linux kernel must be compiled with kdb support enabled. This often involves setting specific configuration options in the kernel (CONFIG_KDB, CONFIG_DEBUG_KERNEL, and others related to debugging features.

Entering kdb

SysRq Trigger:

On systems where the Magic SysRq key is enabled, you can enter kdb by pressingg a skecific key combination. For example holding Alt + SysRq (often Print Screen on keyboards) + g can switch the system to kdb mode.

Breakpoint or Panic:

The system might also automatically enter kdb in response to a kernel breakpoint or panic.

Frequently used kdb commands

bt or backtrace

Display the call stack of the current or a specific CPU. This is useful for understanding the function call sequence leading up to a crash or breakpoint.

md

Display memory contents at a given address

rd

Display the contens of the current CPU registers.

ps

Show process status

lsmod

List loaded kernel modules

set

Set the value of a kernel variable.

clear

Clear a breakpoint

bl

List breakpoints

go

Continue

help

Print help information.