Re: UART question

[Alexander Schreiber <als%thangorodrim.ch@localhost>]

On Fri, Jul 11, 2025 at 06:24:28AM -0400, Mouse wrote:
> >> I suspect that this is behaviour that you have learned because Linux
> >> makes it hard to use dmesg.
> > What are you talking about?
> 
> > $ uname -a;id -u; dmesg |sed 1q
> > Linux flying-carpet 6.12.30-current-sunxi #1 SMP Thu May 22 12:29:54 UTC
> > 2025 armv7l GNU/Linux
> > 1000
> > [    0.000000] Booting Linux on physical CPU 0x0
> > $ 
> 
> Probably more or less this:
> 
> $ uname -a; id -u; dmesg | sed 1q
> Linux mouchine 5.15.0-86-generic #96-Ubuntu SMP Wed Sep 20 08:23:49 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux
> 1001
> dmesg: read kernel buffer failed: Operation not permitted
> $ 
> 
> I'm not Linux expert enough to more than guess at why the difference.

The kernel default for some time has been kernel.dmesg_restrict=1 which
disables reading the kernel log buffer for !root. Various distributions,
however set this differently. The default on e.g. Debian is that
/etc/sysctl.conf has some examples, but is purely comments. Other
distribution might explicitly set kernel.dmesg_restrict=0 to keep the
old behaviour of the kernel log buffer being world readable.

Kind regards,
          Alex.
-- 
"Opportunity is missed by most people because it is dressed in overalls and
 looks like work."                                      -- Thomas A. Edison