Re: [gentoo-user] Re: How to poweroff the system from user?

[Philip Webb]

150322 Peter Humphrey wrote:
> On Sunday 22 March 2015 13:04:44 Nikos Chantziaras wrote:
>>> I can reboot the system when I am a user by Ctrl+Alt+Delete.
>>> The user can reboot the system, but can't shut down ?  Strange
>> The thinking is that you can unplug the machine
>> or press the hardware reset or power button or flip the PSU switch ...
>> Preventing a ctrl+alt+del reboot does not add anything to security.
>> Security doesn't apply to users with physical access to the machine.
>> However, this is just a default. You can easily disable reboot
>> on ctrl+alt+del by editing /etc/inittab and commenting-out this line:
>>   ca:12345:ctrlaltdel:/sbin/shutdown -r now

Testing my single-user box with the above line in  inittab ,
I find that if I enter 'A-^Del' , I exit X to the raw terminal ;
another 'A-^Del' then reboots the box.  If I enter 'shutdown -r now' as user,
I get "shutdown: you must be root to do that!".  'cd /sbin ; ls -l shutdown'
shows '-rwxr-xr-x 1 root root 23192 May 17 2014 shutdown',
so that behaviour arises from the shutdown script, not the permissions.

The 1st effect is explained in  ~/.fluxbox/keys  by
  # exit fluxbox
  Control Mod1 Delete :Exit

However, the 2nd effect is not explained so easily :
'A-^Del' reboots when entered at a raw terminal,
but 'shutdown -r now' does not, yet the former is defined as the latter
by the line above in my  /etc/inittab .

The cause seems to be that 'A-^Del' is intercepted by 'init' (Process 1),
which is owned by root, but 'shutdown -r now' is heard by Process 910
-- 'bash' running in the raw terminal, which was started by 'init' -- ,
which is owned by my user.

So the behaviour is explained, but following my earlier msg,
which advised to follow proper Unix principles,
I should comment the 'A-^Del' line in  inittab :
if the raw terminal can't react to 'su', it won't react to 'A-^Del' either,
so there's no justification in terms of escaping from an emergency.

>> pressing the reset button is far worse, since there's no clean shutdown,
>> unmounting filesystems after flushing caches, etc.

Yes : that's forced only when the keyboard ceases to respond.

>> Because of that, the default of allowing ctrl+alt+del for local users
>> makes more sense than disabling it.

That doesn't follow : if you have multiple users,
you don't want some rogue user rebooting randomly ;
it makes sense only as a convenience on a single-user system.
It seems to be the default behaviour of 'inittab'
-- there no comment saying I set it myself, which I would have added -- ,
which is not appropriate for Gentoo systems in general,
some of which are undoubtedly multi-user.

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