Securing the Console

glock19 · 05-01-2003, 05:19 PM

When setting up a linux system, I routinely disable the trapping of "CTRL+ALT+DEL" , to prevent any user from walking up to my system and rebooting it.

But there are other keyboard commands I want to know how to disable. Especially, "CTRL+ALT+BACKSPACE". This kills the entire X session, and brings the system to a command prompt (fully logged in with my user account). The CTRL+ALT+BACKSPACE even works if I have Xscreensaver with a locked screen. Since I start in runlevel 3, a user could kill X, and get access to my home directory, even if I have the Xscreensaver locking the screen! So, how do I disable the CTRL+ALT+BACKSPACE functionality?

There are other keys I want to disable. For example, "CTRL+ALT+F1" brings the user to the command line where I have my X session running from. All a user would have to do is hit "CTRL+ALT+F1" and then press "CTRL+C" and kill the X session. They would then have access to a command line with my logged in user account. How do I disable this one also?

THANKS, I appreciate anyone who can solve this problem. Thanks again!

Tinkster · 05-01-2003, 05:57 PM

Quote:

But there are other keyboard commands I want to know how to disable. Especially, "CTRL+ALT+BACKSPACE".

in /etc/X11/XF86Config, find
# Option "DontZap"
and remove the #

Quote:

There are other keys I want to disable. For example, "CTRL+ALT+F1" brings the user to the command line where I have my X session running from. All a user would have to do is hit "CTRL+ALT+F1" and then press "CTRL+C" and kill the X session. They would then have access to a command line with my logged in user account. How do I disable this one also?

To work around this problem I'd recommend the
usage of xdm or something the like, run from
rc.local, rather than you starting X manually...

Cheers,
Tink

glock19 · 05-01-2003, 06:00 PM

Pattern not found: DontZap

Tinkster · 05-01-2003, 06:06 PM

Just add it, then ;)
It lives in the section ServerFlags

Code:

Section "ServerFlags"

# Uncomment this to disable the <Crtl><Alt><BS> server abort sequence
# This allows clients to receive this key event.

#    Option "DontZap"

Cheers,
Tink

glock19 · 05-01-2003, 06:10 PM

Pattern not found: ServerFlags

I guess I can just add the section, anywhere in the file?

Tinkster · 05-01-2003, 06:12 PM

Quote:

I guess I can just add the section, anywhere in the file?

Yep :)

Cheers,
Tink

P.S.: Are you actually looking at XF86Config-File
that is used by your XServer? It might be called
XF86Config-4... If it is, though, RedHat sucks
even more than I thought ;)

glock19 · 05-01-2003, 06:21 PM

Great, thanks. That worked.

Now, the only problem remaining is to disable the "CTRL+ALT+F1" ability. Any ideas on how to do that, without switching to xdm/gdm/kdm managers? I *like* booting into runlevel 3 and starting X with "startx" command. I want to keep it that way.

Tinkster · 05-01-2003, 06:25 PM

startx&

after a few seconds

CTRL-ALT-F1

exit

:)

Cheers,
Tink

green_dragon37 · 05-01-2003, 06:29 PM

you could use screen. after you login, type "screen" then "startx," switch back to Console and hit ctrl-x to lock screen

glock19 · 05-01-2003, 06:35 PM

Tinkster, thanks. startx& method works great.

Now my console is protected, yippie! (Unless there is anything I missed? Is there?) Besides the actual physical computer, that is.

Tinkster · 05-01-2003, 06:47 PM

Glad I could be of some help :)

I don't think that there's more problems
with access to your user (besides the
brute physique :})

Cheers,
Tink