How to Completely Disable ‘Kernel Address Space Layout Randomization’ (KASLR) in Ubuntu

Modern Linux kernels, including those shipped with Ubuntu Server, utilize a crucial security feature known as Kernel Address Space Layout Randomization (KASLR). By default, every time your server boots up, the operating system places the core kernel code and its associated data structures into completely random, unpredictable locations in physical memory.

This randomization is an incredibly effective defense against advanced malware and buffer overflow exploits. Because an attacker cannot mathematically predict where the kernel is sitting in memory, it becomes extremely difficult for them to inject malicious code into a privileged execution space. However, this exact same randomization makes low-level kernel development, driver debugging, and performance profiling nearly impossible. If a custom kernel module crashes, the resulting memory dump is useless because the memory addresses shift on every reboot. If you are a kernel developer who requires deterministic, absolute memory addresses for debugging purposes using tools like perf or kgdb, you must completely disable KASLR.

Disabling KASLR via GRUB Bootloader

Because KASLR is enforced at the very beginning of the boot sequence before the operating system even fully loads, you cannot disable it via sysctl or a systemd service. You must pass a hardcoded parameter directly to the kernel via the bootloader.

1. Open a Terminal session (or connect to your server via SSH).
2. Open the primary GRUB configuration file in a text editor with root privileges:
   sudo nano /etc/default/grub
3. Look for the line that begins with GRUB_CMDLINE_LINUX_DEFAULT=. (It usually looks like GRUB_CMDLINE_LINUX_DEFAULT="quiet splash" on desktop versions, or it may be completely blank between the quotes on servers).
4. You must insert the specific kernel parameter nokaslr inside the quotation marks. The line should now look something like this:
   GRUB_CMDLINE_LINUX_DEFAULT="quiet splash nokaslr"
5. Save the file (Ctrl + O, then Enter) and exit the text editor (Ctrl + X).
6. Force the bootloader to compile the new configuration file:
   sudo update-grub
7. Reboot your server immediately for the changes to take effect:
   sudo reboot

Extreme Warning: Your Ubuntu server is now significantly more vulnerable to memory-based exploitation. The kernel will load into the exact same, predictable memory registers on every single boot. You should only use the nokaslr flag in isolated development, testing, or debugging environments, and never on a production server exposed to the public internet.