Hitchhiker's Guide to Openbsd

Note: this will not work on all video cards. Unfortunately, not all video cards support the uploaded 
fonts that 
wscons(4)
requires to achieve the 80x50 text mode. In these cases, you might wish to consider 
running X. 
7.6 - How do I use a serial console?
There are many reasons you may wish to use a serial console for your OpenBSD system: 
●
Recording console output (for documentation). 
●
Remote management. 
●
Easier maintenance of a large quantity of machines 
●
Providing a useful dmesg from machines which might otherwise be difficult to get one from. 
●
Providing an accurate "trace" and "ps" output if your system crashes so developers can have a 
chance to fix the problem. 
OpenBSD supports serial console on most platforms, however details vary greatly between platforms. 
Note that serial interfacing is NOT a trivial task -- you will often need unusual cables, and ports are not 
standardized between machines, in some cases, not even consistent on one machine. It is assumed you 
know how to select the appropriate cable to go between your computer and the device acting as your 
serial terminal. A full tutorial on serial interfacing is beyond the scope of this article, however, we offer 
one hint: just because the ends plug in doesn't mean it will work. 
/etc/ttys change
There are two parts to getting a functional serial console on an OpenBSD system. First, you must have 
OpenBSD use your serial port as a console for status and single user mode. This part is very platform 
dependent. Second, you must enable the serial port to be used as an interactive terminal, so a user can 
log into it when running multi-user. This part is fairly similar between platforms, and is detailed here. 
Terminal sessions are controlled by the 
/etc/ttys
file. Before OpenBSD will give you a "
login:
" 
prompt at a device, it has to be enabled in /etc/ttys, after all, there are other uses for a serial port other 
than for a terminal. In platforms which typically have an attached keyboard and screen as a console, the 
serial terminal is typically disabled by default. We'll use the i386 platform as an example. In this case, 
you must edit the line that reads: 
tty00 "/usr/libexec/getty std.9600" unknown off
http://www.openbsd.org/faq/faq7.html (4 of 14)9/4/2011 10:02:08 AM

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7 - Keyboard and Display Controls
to read something like: 
tty00 "/usr/libexec/getty std.9600" vt220 on secure
Here, 
tty00
is the serial port we are using as a console. 
vt220
 is the 
termcap(5)
entry that matches 
YOUR terminal (other likely options might include 
vt100
, 
xterm
, etc.). The "
on
" activates the 
getty
for that serial port so that a "
login:
" prompt will be presented, the "
secure
" permits a root (uid 0) 
login at this console (which may or may not be what you desire), and the "
9600
" is the terminal baud 
rate. Resist the urge to crank the baud rate up to the maximum your hardware can support, as you are 
more likely to create problems than benefit. Most systems have a "default" speed (supported by default 
by the boot ROM and/or the boot loader, often 9600), use this unless you have real reason to use 
something different. 
Note that you can use a serial console for install without doing this step, as the system is running in 
single user mode, and not using getty for login. 
On some platforms and some configurations, you must bring the system up in single user mode to make 
this change if a serial console is all you have available.