Two System Settings

Two System Settings

Checking them, fixing them, and finding the file that keeps putting them back.

Two settings, both worth points

sysctl kernel.randomize_va_space net.ipv4.ip_forward

Setting	Should be	What it does
`kernel.randomize_va_space`	`2`	loads programs at a different place in memory each time, which breaks most memory attacks
`net.ipv4.ip_forward`	`0`	stops this machine passing other people's network traffic along

Change them now

sudo sysctl -w kernel.randomize_va_space=2
sudo sysctl -w net.ipv4.ip_forward=0

That takes effect immediately. It does not survive a restart, which is the next problem.

Find what keeps putting them back

ls /etc/sysctl.d/

Everything in that folder is applied at every restart. Ubuntu ships a couple of files here, so look for one that does not belong and open it:

sudo nano /etc/sysctl.d/FILENAME

If it sets either of the two settings above to the wrong value, delete the file:

sudo rm /etc/sysctl.d/FILENAME

💡 If a setting keeps coming back wrong after a restart, something is putting it back. Stop re-running the command and go find the file. This is the same shape as the problem in the next lesson.

Try it yourself

sysctl kernel.randomize_va_space net.ipv4.ip_forward   # what they are now
ls /etc/sysctl.d/                                       # what runs at every restart
sudo nano /etc/sysctl.d/FILENAME                        # read anything unfamiliar

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Two settings, both worth points

Change them now

Find what keeps putting them back

Try it yourself

Do this lesson for real