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Message |
Peter Wemm
*nix forums Guru Wannabe
Joined: 11 Apr 2002
Posts: 113
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 Posted: Mon Jun 12, 2006 10:07 pm Post subject:
Re: A sort of plan for consoles in FreeBSD
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On Sunday 28 May 2006 01:05, Poul-Henning Kamp wrote:
| Quote: | In message <20060528.011518.1306332021.imp@bsdimp.com>, "M. Warner
Losh" writes
In message: <16029.1148764704@critter.freebsd.dk
Poul-Henning Kamp <phk@phk.freebsd.dk> writes:
: 4. The /dev/console device in multi-user mode.
: Emergency output device for critical messages.
Who is generating these messages?
Typically programs in distress.
|
FWIW. The syslog(3) library call will open /dev/console if it cannot
connect to the syslog socket and LOG_CONS is set.
--
Peter Wemm - peter@wemm.org; peter@FreeBSD.org; peter@yahoo-inc.com
"All of this is for nothing if we don't go to the stars" - JMS/B5
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Julian Elischer
*nix forums Guru Wannabe
Joined: 20 Mar 2002
Posts: 279
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| Posted: Tue May 30, 2006 6:23 pm Post subject:
Re: A sort of plan for consoles in FreeBSD
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M. Warner Losh wrote:
| Quote: | In message: <86pshx85tu.fsf@xps.des.no
des@des.no (Dag-Erling Smørgrav) writes:
: "M. Warner Losh" <imp@bsdimp.com> writes:
: > There's no way to 'connect to syslogd and subscribe to messages' in
: > the current syslogd.
:
: tail -F /var/log/messages
|
in -currnet you can listen on any UDP port and have syslog send you stuff.
| Quote: | That doesn't give you what I described. What that does is give you
the messages that syslogd writes to /var/log/messages. This is a
subset of the messages sent to syslogd, and doesn't have the severity
levels, facilities, etc associated with them. There's no way for one
to connect to syslogd and dynamically filter the records that are
displayed. While adding such a facility wouldn't be that hard, it
does not exist today.
Warner
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Poul-Henning Kamp
*nix forums Guru
Joined: 21 Mar 2002
Posts: 436
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| Posted: Tue May 30, 2006 6:03 pm Post subject:
Re: A sort of plan for consoles in FreeBSD
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In message <20060530135814.A70588@grasshopper.cs.duke.edu>, Andrew Gallatin wri
tes:
| Quote: | Poul-Henning Kamp [phk@phk.freebsd.dk] wrote:
I would like to redefine the semantics of "/dev/console" as follows:
if any console-consumers like xconsole( are active
send output to all console-consumers.
else if a controlling terminal is available
send output to controlling terminal (that is /dev/tty)
else
send output to syslogd, as if generated by printf(9).
(but do not actually output to low-level console)
If there is nobody logged in, where do kernel messages from device
drivers, and panic messages (with helpful things like KDB_TRACE) wind
up?
|
These go to the #2 console just like the bootup messages etc.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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Andrew Gallatin
*nix forums addict
Joined: 18 Jul 2002
Posts: 52
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| Posted: Tue May 30, 2006 5:58 pm Post subject:
Re: A sort of plan for consoles in FreeBSD
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Poul-Henning Kamp [phk@phk.freebsd.dk] wrote:
| Quote: | I would like to redefine the semantics of "/dev/console" as follows:
if any console-consumers like xconsole( are active
send output to all console-consumers.
else if a controlling terminal is available
send output to controlling terminal (that is /dev/tty)
else
send output to syslogd, as if generated by printf(9).
(but do not actually output to low-level console)
|
If there is nobody logged in, where do kernel messages from device
drivers, and panic messages (with helpful things like KDB_TRACE) wind
up? I hope the answer is not "nowhere". I have debugged many
problems after they happened by looking at serial console logs,
and I would hate to loose this.
Drew
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M. Warner Losh
*nix forums Guru
Joined: 22 Mar 2002
Posts: 365
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| Posted: Mon May 29, 2006 5:29 pm Post subject:
Re: A sort of plan for consoles in FreeBSD
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In message: <86pshx85tu.fsf@xps.des.no>
des@des.no (Dag-Erling Smørgrav) writes:
: "M. Warner Losh" <imp@bsdimp.com> writes:
: > There's no way to 'connect to syslogd and subscribe to messages' in
: > the current syslogd.
:
: tail -F /var/log/messages
That doesn't give you what I described. What that does is give you
the messages that syslogd writes to /var/log/messages. This is a
subset of the messages sent to syslogd, and doesn't have the severity
levels, facilities, etc associated with them. There's no way for one
to connect to syslogd and dynamically filter the records that are
displayed. While adding such a facility wouldn't be that hard, it
does not exist today.
Warner
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Poul-Henning Kamp
*nix forums Guru
Joined: 21 Mar 2002
Posts: 436
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| Posted: Mon May 29, 2006 10:49 am Post subject:
Re: A sort of plan for consoles in FreeBSD
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In message <86pshx85tu.fsf@xps.des.no>, Dag-Erling =?iso-8859-1?Q?Sm=F8rgrav?=
writes:
| Quote: | "M. Warner Losh" <imp@bsdimp.com> writes:
There's no way to 'connect to syslogd and subscribe to messages' in
the current syslogd.
tail -F /var/log/messages
|
Yes, that is sort of a substitute, but not quite...
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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Dag-Erling Smørgrav
*nix forums Guru Wannabe
Joined: 16 Mar 2003
Posts: 186
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| Posted: Mon May 29, 2006 10:48 am Post subject:
Re: A sort of plan for consoles in FreeBSD
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"M. Warner Losh" <imp@bsdimp.com> writes:
| Quote: | There's no way to 'connect to syslogd and subscribe to messages' in
the current syslogd.
|
tail -F /var/log/messages
DES
--
Dag-Erling Smørgrav - des@des.no
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Doug Barton
*nix forums addict
Joined: 24 Apr 2002
Posts: 91
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| Posted: Sun May 28, 2006 6:08 pm Post subject:
Re: A sort of plan for consoles in FreeBSD
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Poul-Henning Kamp wrote:
| Quote: | In message <4478F767.5090403@FreeBSD.org>, Doug Barton writes:
At first glance I don't see anything wrong with that logic. My one request
is that you add a branch that says, "if legacy behavior is requested by
some configuration method>, add it to the mix."
Legacy behaviour is exactly what we need to avoid to get the
device locking sorted out, so this would be rather poisonous
to the entire effort.
|
Just to be clear, I'm not saying that the mechanism for making it happen has
to be the same, just that having the same end result would be very useful.
Doug
--
This .signature sanitized for your protection
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Poul-Henning Kamp
*nix forums Guru
Joined: 21 Mar 2002
Posts: 436
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| Posted: Sun May 28, 2006 5:51 pm Post subject:
Re: A sort of plan for consoles in FreeBSD
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In message <20060528.113724.1655407378.imp@bsdimp.com>, "M. Warner Losh" writes
:
| Quote: | Why we can't do as I suggested earlier and just make /dev/console a
pseudo-pipe that is fed from #2 and #4 and that has a well documented
'other end interface' for things like xconsole. that would simulate
the historical usage of /dev/console well.
|
We probably _can_ do that, but it would be easier to teach syslogd
about accept connections from processes interested in subscribing
to events.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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M. Warner Losh
*nix forums Guru
Joined: 22 Mar 2002
Posts: 365
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| Posted: Sun May 28, 2006 5:37 pm Post subject:
Re: A sort of plan for consoles in FreeBSD
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In message: <1471.1148836757@critter.freebsd.dk>
"Poul-Henning Kamp" <phk@phk.freebsd.dk> writes:
: In message <4479D804.1060106@elischer.org>, Julian Elischer writes:
: >M. Warner Losh wrote:
: >
: >>In message: <4479C171.4050403@elischer.org>
: >> Julian Elischer <julian@elischer.org> writes:
: >>: killing XConsole is not a small matter. people have that when they are
: >>: specifically looking for that information
: >>
: >>Recall that this is only for programs that open /dev/console directly
: >>and write to it, like syslogd.
: >
: >the description makes it sound like xconsole would not be able to show
: >kernel error messages.
:
: xconsole is a hack anyway.
:
: the correct way would be to have way to connect to syslogd and subscribe
: to messages.
There's no way to 'connect to syslogd and subscribe to messages' in
the current syslogd. In today's world order, the best that it can do
is to open a pty, and then hack syslogd.conf to send messages to that
pty and then log the results. This takes quiet a bit of code, and
there's a number of tricky edge cases to make it work. At least there
were back when I created a combination xconsole + syslog display
program. And I still didn't have the ability to filter on message
time except in real time (since syslogd doesn't print message type).
I also had to have two PTYs open (one for syslog messages and one for
console messages). If you are going to go down this route, lots of
work needs to happen to both xconsole and syslogd (and all other
xconsole-like programs).
Not saying that it can't be done, but there's a big hunk of work there
before people would be happy.
Why we can't do as I suggested earlier and just make /dev/console a
pseudo-pipe that is fed from #2 and #4 and that has a well documented
'other end interface' for things like xconsole. that would simulate
the historical usage of /dev/console well.
Warner
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Poul-Henning Kamp
*nix forums Guru
Joined: 21 Mar 2002
Posts: 436
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| Posted: Sun May 28, 2006 5:19 pm Post subject:
Re: A sort of plan for consoles in FreeBSD
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In message <4479D804.1060106@elischer.org>, Julian Elischer writes:
| Quote: | M. Warner Losh wrote:
In message: <4479C171.4050403@elischer.org
Julian Elischer <julian@elischer.org> writes:
: killing XConsole is not a small matter. people have that when they are
: specifically looking for that information
Recall that this is only for programs that open /dev/console directly
and write to it, like syslogd.
the description makes it sound like xconsole would not be able to show
kernel error messages.
|
xconsole is a hack anyway.
the correct way would be to have way to connect to syslogd and subscribe
to messages.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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Julian Elischer
*nix forums Guru Wannabe
Joined: 20 Mar 2002
Posts: 279
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| Posted: Sun May 28, 2006 5:04 pm Post subject:
Re: A sort of plan for consoles in FreeBSD
|
|
|
M. Warner Losh wrote:
| Quote: | In message: <4479C171.4050403@elischer.org
Julian Elischer <julian@elischer.org> writes:
: killing XConsole is not a small matter. people have that when they are
: specifically looking for that information
Recall that this is only for programs that open /dev/console directly
and write to it, like syslogd.
|
the description makes it sound like xconsole would not be able to show
kernel error messages.
| Quote: | Warner
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M. Warner Losh
*nix forums Guru
Joined: 22 Mar 2002
Posts: 365
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| Posted: Sun May 28, 2006 4:46 pm Post subject:
Re: A sort of plan for consoles in FreeBSD
|
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|
In message: <4479C171.4050403@elischer.org>
Julian Elischer <julian@elischer.org> writes:
: killing XConsole is not a small matter. people have that when they are
: specifically looking for that information
Recall that this is only for programs that open /dev/console directly
and write to it, like syslogd.
Warner
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Julian Elischer
*nix forums Guru Wannabe
Joined: 20 Mar 2002
Posts: 279
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| Posted: Sun May 28, 2006 3:27 pm Post subject:
Re: A sort of plan for consoles in FreeBSD
|
|
|
Poul-Henning Kamp wrote:
| Quote: | In message <20060528.011518.1306332021.imp@bsdimp.com>, "M. Warner Losh" writes
:
In message: <16029.1148764704@critter.freebsd.dk
Poul-Henning Kamp <phk@phk.freebsd.dk> writes:
: 4. The /dev/console device in multi-user mode.
: Emergency output device for critical messages.
Who is generating these messages?
Typically programs in distress.
If so, why not make /dev/console a pipe that syslogd listens to?
That is the option which I personally favour.
It kills xconsole(1) like applications, and I suspect that would
result in whinage, but if we are willing to do that, it is by
far the simplest and most sensible solution.
killing XConsole is not a small matter. people have that when they are |
specifically looking for that information
| Quote: |
: I would like to redefine the semantics of "/dev/console" as follows:
: if any console-consumers like xconsole( are active
: send output to all console-consumers.
: else if a controlling terminal is available
: send output to controlling terminal (that is /dev/tty)
: else
: send output to syslogd, as if generated by printf(9).
: (but do not actually output to low-level console)
Assuming that this is for #4 /dev/console, that's fine.
It is only #4.
The problem that I
have with it being just /dev/tty is that the program opened
/dev/console to tell the world about it, rather than just using
fprintf(stderr,). What does that gain you?
As I said in the other email, /dev/tty and stderr is not quite the
same thing. /dev/tty has more of the semantics that /dev/console
used to have (ie: flash it before their eyes).
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Poul-Henning Kamp
*nix forums Guru
Joined: 21 Mar 2002
Posts: 436
|
| Posted: Sun May 28, 2006 8:07 am Post subject:
Re: A sort of plan for consoles in FreeBSD
|
|
|
In message <4478F767.5090403@FreeBSD.org>, Doug Barton writes:
| Quote: | At first glance I don't see anything wrong with that logic. My one request
is that you add a branch that says, "if legacy behavior is requested by
some configuration method>, add it to the mix."
|
Legacy behaviour is exactly what we need to avoid to get the
device locking sorted out, so this would be rather poisonous
to the entire effort.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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