linux-kernel - Re: [PATCH 5/5] ptrace: it is fun to strace /sbin/init

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Message-ID: <20080320165756.GA11197@tv-sign.ru>
Date:	Thu, 20 Mar 2008 19:57:56 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Pavel Machek <pavel@....cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Davide Libenzi <davidel@...ilserver.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Ingo Molnar <mingo@...e.hu>,
	Laurent Riffard <laurent.riffard@...e.fr>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] ptrace: it is fun to strace /sbin/init

On 03/20, Pavel Machek wrote:
> 
> > Ptracing of /sbin/init is not allowed. Of course, this is very dangerous, but
> > may be useful. Introduce the kernel boot parameter to allow this.
> ...
> > @@ -803,6 +803,8 @@ and is between 256 and 4096 characters. 
> >  			Run specified binary instead of /sbin/init as init
> >  			process.
> >  
> > +	init_ptrace	[KNL] Allows to ptrace init. Very dangerous. Don't use.
> > +
> 
> I don't know what ptracing init is good for, and I believe people
> wanting to do this kind of special stuff can patch their own kernel...

Yes sure. But could you explain why this can be bad given that ptracing
init needs the explicit boot parameter? IOW, could you explain why you
don't like this small and trivial change which adds a minimal impact ?

Most of the lkml readers can easily implement most of debugging options,
do you mean there are useless? I personally like the possibility to trace
init without re-compiling the kernel, because I'd like to know why /usr/bin/top
sometimes shows init at the top.

Oleg.

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