freebsd stable - Nov 2018 - sudo not available after configuring ipmi serial over lan

On Thu, 2018-11-08 at 12:47 -0500, Jordan Caraballo
wrote:
> Hi Ian,
> Changing the line following line from std.115200 to 3wire.115200
> worked.
> Can you explain the why? I am not entirely sure of the difference
> between
> 3wire and std there.
> 
> ttyu0???"/usr/libexec/getty 3wire.115200"
vt100???on??????????secure
> 
> Thanks,
> - Jordan
> 
The standard setting honors the modem control lines on the serial port,
so any attempt to open that serial device will block until the carrier-
detect line on the port is asserted.

The 3wire setting indicates that only RX, TX, and GND are connected,
and modem-control signals should be ignored. An open of such a device
will return immediately whether anything is actually connected to the
serial port or not.

A /dev/ttyN device is assumed to be a "call-in" device and has the
blocking behavior by default. A /dev/cuaN device is assumed to be a
"call-out" device that doesn't wait for modem carrier by blocking.
Using the std vs 3wire designations in /etc/ttys causes init(1) to set
termios(4) flags to implement blocking-open or immediate-open behavior
without needing to change the device name as well.

-- Ian
> El jue., 8 nov. 2018 a las 10:39, Ian Lepore (<ian at freebsd.org>)
> escribi?:
> 
> > 
> > On Thu, 2018-11-08 at 06:10 +0700, Eugene Grosbein wrote:
> > > 
> > > 08.11.2018 5:56, Jordan Caraballo wrote:
> > > 
> > > > 
> > > > 
> > > > Hi guys,
> > > > 
> > > > After configuring ipmi serial over lan console, I am not
being
> > > > able
> > > > to
> > > > execute any command related to sudo; not even "sudo su
-". I am
> > > > using ttyu0
> > > > and COM1 on a Dell R530. Everything regarding receiving
output
> > > > and
> > > > typing
> > > > at the serial console is fine; the only command not working
is
> > > > sudo.
> > > > 
> > > > Any ideas? Below are the configurations.
> > > > 
> > > > /etc/ttys
> > > > 
> > > > # Serial terminals
> > > > # The 'dialup' keyword identifies dialin lines to
login,
> > > > fingerd
> > > > etc.
> > > > #ttyu0??"/usr/libexec/getty
3wire"??????vt100???onifconsole
> > > > secure
> > > > ttyu0???"/usr/libexec/getty std.115200"
> > > > vt100???on??????????secure
> > > Use network access to perform the following:
> > > 
> > > 1) Change "on" to "off" for ttyu0 then run
"init q" to apply
> > > changes.
> > > 2) Replace "ttyu0" with "cuau0" within same
line then run "init
> > > q"
> > > again.
> > > 
> > > Then retry using console and sudo.
> > The easy way to accomplish the same thing is to change std.115200
> > to
> > 3wire.115200 (and then do 'init q').
> > 
> > -- Ian
> > 
>

What I find interesting is that with the 'wrong' setting, you can log
still
in just fine, and run most commands, but 'sudo' alone fails as described
above. (I've had the same experience on Serial-over-IPMI, but 'su'
worked
fine so I never dug into it.)

It's an easy fix, but I'm still (academically) interested in what it is
that sudo is doing that is unique.

 - Eric