I am using Ubuntu 12.04 32-bits now for some experiment I need to disable ASLR how can I do this? and after that what should I do to enable ASLR again?

up vote 65 down vote accepted

According to an article How Effective is ASLR on Linux Systems?, you can configure ASLR in Linux using the /proc/sys/kernel/randomize_va_space interface.

The following values are supported:

  • 0 – No randomization. Everything is static.
  • 1 – Conservative randomization. Shared libraries, stack, mmap(), VDSO and heap are randomized.
  • 2 – Full randomization. In addition to elements listed in the previous point, memory managed through brk() is also randomized.

So, to disable it, run

echo 0 | sudo tee /proc/sys/kernel/randomize_va_space

and to enable it again, run

echo 2 | sudo tee /proc/sys/kernel/randomize_va_space

This won't survive a reboot, so you'll have to configure this in sysctl. Add a file /etc/sysctl.d/01-disable-aslr.conf containing:

kernel.randomize_va_space = 0

should permanently disable this.

The /proc/sys/kernel/randomize_va_space interface controls ASLR system-wide.

If you don't want a system-wide change, use ADDR_NO_RANDOMIZE personality to temporarily disable ASLR. Controlling this personality flag can be done with setarch and its -R option (manpage), prepending a command.

I find it really convenient to open a completely new shell using:

setarch `uname -m` -R /bin/bash

This will open a new Bash shell for you with ASLR disabled, including all child processes (programs run from this shell).

Just exit the shell once you're done.

By the way, on i386, ulimit -s unlimited can "disable" ASLR.

EDIT (Apr 2016): The ulimit -s unlimited was fixed and assigned CVE-2016-3672.

  • Minor detail in the spirit of util-linux: instead of uname -m one could also use arch, a binary that essentially does the same. – drumfire Jan 8 '16 at 15:16
  • 1
    @drumfire arch is not available as a busybox applet – zhangyoufu Oct 29 '16 at 3:25
  • +1 for coming back two years later and adding the information regarding CVE. – Multisync Apr 16 at 7:37

The more permanent ways of disabling ASLR should be kept in a VM for obvious reasons.

to test the ability to overwrite stack frame return addresses etcetera, you'll need to compile without stack canaries -fno-stack-protector, while to allow you to execute code on the stack you need to compile with -z execstack, making

$ gcc -fno-stack-protector -z execstack -o <my_program> my_code.c

You can just use sudo sysctl kernel.randomize_va_space=0 to temparaly disable ASLR.

Your Answer

By clicking "Post Your Answer", you acknowledge that you have read our updated terms of service, privacy policy and cookie policy, and that your continued use of the website is subject to these policies.

Not the answer you're looking for? Browse other questions tagged or ask your own question.