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Subject: Re: Dual Consoles: Is there any way to have the output of startup
 scripts to go to both?
Date: Tue, 16 Aug 2022 15:25:09 -0400
In-Reply-To: <CACNAnaEv7tEsffixjL4yGwWJiCCEok3q=q2hK5zCNvZtSvF1FQ@mail.gmail.com>
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To: Kyle Evans <kevans@freebsd.org>
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> On Aug 16, 2022, at 15:01, Kyle Evans <kevans@freebsd.org> wrote:
>=20
> On Tue, Aug 16, 2022 at 11:34 AM Dan Mahoney <freebsd@gushi.org =
<mailto:freebsd@gushi.org>> wrote:
>>=20
>> Hey there all,
>>=20
>> At the day job we have dell idrac machines that also do serial =
consoles (this is super convenient because you can get a serial console =
by ssh'ing to the idrac), instead of firing up a browser and a VPN (and, =
earlier, Java...eww).
>>=20
>> So naturally, in /boot/loader.conf we set =
console=3Dcomconsole,vidconsole.
>>=20
>> We get dmesg output out both consoles.  We ultimately wind up with a =
login prompt on both consoles, but the output of boot scripts only go to =
one, and if the system craps the bed and drops to single-user mode, one =
console just "hangs" and the other one gives you useful output.
>>=20
>> It feels pretty trivial to have /etc/rc detect this unique condition, =
and perhaps put *some* output out to the inactive console, even if it's =
not capable of letting you do something interactive like an fsck from =
both.  Just something that hints "hey, go check the other line, there's =
things happening over there".
>>=20
>> How hard would this be?
>>=20
>=20
> I have some WIP that will scattershot console output to all configured
> consoles, but right now there's not really a way to configure userland
> output to go to non-primary consoles.

Dmesg at least seems to already do this.

It looks like the thing that handles sending output to the console is =
actually "init" per the line at the top of /etc/rc.  Init sends to =
/dev/console, I'm guessing, and /dev/console can be only one device.

Making rc bit detect and bit-bang unused consoles feels like asking for =
problems.

That said, sysctl -a | grep console has these things:

kern.always_console_output: 0
kern.log_console_add_linefeed: 0
kern.log_console_output: 1
kern.console: ttyv0,/uart,ttyv0,gdb,
debug.witness.output_channel: console

Can someone tell me what manpage would tell me more about the =
kern.console variable?

-Dan=

--Apple-Mail=_611ED23B-0875-44AC-8BA6-BD032F8438D5
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<html><head><meta http-equiv=3D"Content-Type" content=3D"text/html; =
charset=3Dus-ascii"></head><body style=3D"word-wrap: break-word; =
-webkit-nbsp-mode: space; line-break: after-white-space;" class=3D""><br =
class=3D""><div><br class=3D""><blockquote type=3D"cite" class=3D""><div =
class=3D"">On Aug 16, 2022, at 15:01, Kyle Evans &lt;<a =
href=3D"mailto:kevans@freebsd.org" class=3D"">kevans@freebsd.org</a>&gt; =
wrote:</div><br class=3D"Apple-interchange-newline"><div class=3D""><meta =
charset=3D"UTF-8" class=3D""><span style=3D"caret-color: rgb(0, 0, 0); =
font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: 400; letter-spacing: normal; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
text-decoration: none; float: none; display: inline !important;" =
class=3D"">On Tue, Aug 16, 2022 at 11:34 AM Dan Mahoney &lt;</span><a =
href=3D"mailto:freebsd@gushi.org" style=3D"font-family: Helvetica; =
font-size: 12px; font-style: normal; font-variant-caps: normal; =
font-weight: 400; letter-spacing: normal; orphans: auto; text-align: =
start; text-indent: 0px; text-transform: none; white-space: normal; =
widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; =
-webkit-text-stroke-width: 0px;" class=3D"">freebsd@gushi.org</a><span =
style=3D"caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: =
12px; font-style: normal; font-variant-caps: normal; font-weight: 400; =
letter-spacing: normal; text-align: start; text-indent: 0px; =
text-transform: none; white-space: normal; word-spacing: 0px; =
-webkit-text-stroke-width: 0px; text-decoration: none; float: none; =
display: inline !important;" class=3D"">&gt; wrote:</span><br =
style=3D"caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: =
12px; font-style: normal; font-variant-caps: normal; font-weight: 400; =
letter-spacing: normal; text-align: start; text-indent: 0px; =
text-transform: none; white-space: normal; word-spacing: 0px; =
-webkit-text-stroke-width: 0px; text-decoration: none;" =
class=3D""><blockquote type=3D"cite" style=3D"font-family: Helvetica; =
font-size: 12px; font-style: normal; font-variant-caps: normal; =
font-weight: 400; letter-spacing: normal; orphans: auto; text-align: =
start; text-indent: 0px; text-transform: none; white-space: normal; =
widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; =
-webkit-text-stroke-width: 0px; text-decoration: none;" class=3D""><br =
class=3D"">Hey there all,<br class=3D""><br class=3D"">At the day job we =
have dell idrac machines that also do serial consoles (this is super =
convenient because you can get a serial console by ssh'ing to the =
idrac), instead of firing up a browser and a VPN (and, earlier, =
Java...eww).<br class=3D""><br class=3D"">So naturally, in =
/boot/loader.conf we set console=3Dcomconsole,vidconsole.<br =
class=3D""><br class=3D"">We get dmesg output out both consoles. =
&nbsp;We ultimately wind up with a login prompt on both consoles, but =
the output of boot scripts only go to one, and if the system craps the =
bed and drops to single-user mode, one console just "hangs" and the =
other one gives you useful output.<br class=3D""><br class=3D"">It feels =
pretty trivial to have /etc/rc detect this unique condition, and perhaps =
put *some* output out to the inactive console, even if it's not capable =
of letting you do something interactive like an fsck from both. =
&nbsp;Just something that hints "hey, go check the other line, there's =
things happening over there".<br class=3D""><br class=3D"">How hard =
would this be?<br class=3D""><br class=3D""></blockquote><br =
style=3D"caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: =
12px; font-style: normal; font-variant-caps: normal; font-weight: 400; =
letter-spacing: normal; text-align: start; text-indent: 0px; =
text-transform: none; white-space: normal; word-spacing: 0px; =
-webkit-text-stroke-width: 0px; text-decoration: none;" class=3D""><span =
style=3D"caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: =
12px; font-style: normal; font-variant-caps: normal; font-weight: 400; =
letter-spacing: normal; text-align: start; text-indent: 0px; =
text-transform: none; white-space: normal; word-spacing: 0px; =
-webkit-text-stroke-width: 0px; text-decoration: none; float: none; =
display: inline !important;" class=3D"">I have some WIP that will =
scattershot console output to all configured</span><br =
style=3D"caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: =
12px; font-style: normal; font-variant-caps: normal; font-weight: 400; =
letter-spacing: normal; text-align: start; text-indent: 0px; =
text-transform: none; white-space: normal; word-spacing: 0px; =
-webkit-text-stroke-width: 0px; text-decoration: none;" class=3D""><span =
style=3D"caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: =
12px; font-style: normal; font-variant-caps: normal; font-weight: 400; =
letter-spacing: normal; text-align: start; text-indent: 0px; =
text-transform: none; white-space: normal; word-spacing: 0px; =
-webkit-text-stroke-width: 0px; text-decoration: none; float: none; =
display: inline !important;" class=3D"">consoles, but right now there's =
not really a way to configure userland</span><br style=3D"caret-color: =
rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: =
normal; font-variant-caps: normal; font-weight: 400; letter-spacing: =
normal; text-align: start; text-indent: 0px; text-transform: none; =
white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
text-decoration: none;" class=3D""><span style=3D"caret-color: rgb(0, 0, =
0); font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: 400; letter-spacing: normal; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
text-decoration: none; float: none; display: inline !important;" =
class=3D"">output to go to non-primary =
consoles.</span></div></blockquote></div><br class=3D""><div =
class=3D"">Dmesg at least seems to already do this.</div><div =
class=3D""><br class=3D""></div><div class=3D"">It looks like the thing =
that handles sending output to the console is actually "init" per the =
line at the top of /etc/rc. &nbsp;Init sends to /dev/console, I'm =
guessing, and /dev/console can be only one device.</div><div =
class=3D""><br class=3D""></div><div class=3D"">Making rc bit detect and =
bit-bang unused consoles feels like asking for problems.</div><div =
class=3D""><br class=3D""></div><div class=3D"">That said, sysctl -a | =
grep console has these things:</div><div class=3D""><br =
class=3D""></div><div class=3D""><div =
class=3D"">kern.always_console_output: 0</div><div =
class=3D"">kern.log_console_add_linefeed: 0</div><div =
class=3D"">kern.log_console_output: 1</div><div class=3D"">kern.console: =
ttyv0,/uart,ttyv0,gdb,</div><div class=3D"">debug.witness.output_channel: =
console</div></div><div class=3D""><br class=3D""></div><div =
class=3D"">Can someone tell me what manpage would tell me more about the =
kern.console variable?</div><div class=3D""><br class=3D""></div><div =
class=3D"">-Dan</div></body></html>=

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