Date: Mon, 25 Apr 2016 20:50:15 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Ingo Molnar <mingo@kernel.org>, Borislav Petkov <bp@alien8.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: printk: Add kernel parameter to disable writes to /dev/kmsg
Message-ID: <20160425185015.GJ3448@twins.programming.kicks-ass.net>
References: <20160425130629.188a901c@gandalf.local.home>
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On Mon, Apr 25, 2016 at 01:06:29PM -0400, Steven Rostedt wrote:
> Over the weekend my server was acting funny. The display wasn't working
> well, and I assumed that a driver was going bad. I went to look at the
> kernel dmesg, but the buffer only had the following over and over:
> 
> [226062.401405] systemd-logind[3511]: Removed session 4168.
> [226063.381051] systemd-logind[3511]: Removed session 4169.

> The kernel buffer was completely overridden by useless spewing from

Yes it does this. I usually fix this with: apt-get install sysvinit

> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index bfbf284e4218..b704b48415a0 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -85,6 +85,15 @@ static struct lockdep_map console_lock_dep_map = {
>  };
>  #endif
>  
> +static bool devkmsg_disabled;
> +static int __init disable_devkmsg(char *str)
> +{
> +	devkmsg_disabled = true;
> +	return 0;
> +}
> +__setup("disable_devkmsg_write", disable_devkmsg);
> +

Can't we default enable this? Or at the very least make this easier to
type? I'll never remember how exactly this thing will be called.