User-mode ASLR is usually what is meant by the term ASLR. It being enabled implies this protection to be available on the user space mapping of every process. Effectively, ASLR being enabled implies that the absolute memory map of user-mode processes will vary every time they're run.
ASLR has been supported on Linux for a very long time (since 2005 on 2.6.12). The kernel has a tunable pseudo-file within procfs, to query and set (as root) the ASLR status; here it is: /proc/sys/kernel/randomize_va_space.
It can have three possible values; the three values and their meaning are shown in the following table:
| Tunable value | Interpretation of this value in /proc/sys/kernel/randomize_va_space |
| 0 | (User mode) ASLR turned OFF; or can be turned off by passing the kernel parameter norandmaps at boot. |
| 1 | (User mode) ASLR is ON: mmap(2) based allocations, the stack, and the vDSO page is randomized. It also implies that shared library load locations and shared... |
