docs/180493: Single-user mode console confusion

[Andrew Wright]

>Number:         180493
>Category:       docs
>Synopsis:       Single-user mode console confusion
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-doc
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          doc-bug
>Submitter-Id:   current-users
>Arrival-Date:   Fri Jul 12 14:30:00 UTC 2013
>Closed-Date:
>Last-Modified:
>Originator:     Andrew Wright
>Release:        9.1-RELEASE-p4
>Organization:
Mount Allison University
>Environment:
FreeBSD qemg.org 9.1-RELEASE-p4 FreeBSD 9.1-RELEASE-p4 #0: Mon Jun 17 11:42:37 UTC 2013     root at amd64-builder.daemonology.net:/usr/obj/usr/src/sys/GENERIC  amd64

>Description:
I have these lines in /boot/loader.conf in order to enable a sometimes-installed serial console device:

boot_multicons="YES"
boot_serial="YES"
comconsole_speed="19200"
console="comconsole,vidconsole"


A side effect of these lines is that entering single-user mode produces a prompt only on the external console.  This was extremely confusing when attempting to boot single-user, as all messages prior to the single-user prompt are produced on the vid terminal (and on the external console), however at the moment that single-user mode is entered, the mirroring ceases.  While it is now clear what happened, the effect is that single-user mode appears to be unavailable.

I have no /boot.config file that would indicate which console is meant to be used for messages.


>How-To-Repeat:
Add these lines to /boot/loader.conf, attempt to boot single user.
>Fix:

I would suggest adding some text to the handbook page "Setting up the Serial Console"
http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/serialconsole-setup.html#serialconsole-loader

Currently, these page makes no comment regarding single-user mode whatsoever.  Informing the user that configuring the console may well have repercussions on entry to single-user mode will lessen confusion in the future.


 I would therefore suggest adding the following text into section 26.6.6 "Setting up the Console from the Boot Loader", subsection 26.6.6.1 "Setting Up the Serial Console":


Note that entry to single-user mode will only honour input on one console, even if multiple consoles are indicated using the <tt>console</tt> boot option.  Care must be taken that the first named console is available to the system manager entering single-user mode.


I will note that the first sentence in this section "The boot loader and the kernel to use the serial console can be specified by writing one line in /boot/loader.conf" seems very poorly written -- I do not understand what this line is attempting to say.



Additionally, there is already a section "26.6.7 Caveats"; a note here indicating possible effects on single-user boot would probably not go amiss. 

>Release-Note:
>Audit-Trail:
>Unformatted: