15 - How can I get a dmesg(8) to report an install problem?

When reporting a problem, it is critical to include the complete system dmesg(8). However, often when you need to do this, it is because the system is working improperly or won't install so you may not have disk, network, or other resources you need to get the dmesg to the appropriate mail list. There are other ways, however:
• Floppy disk: The boot disks and CD-ROM have enough tools to let you record your dmesg to an MSDOS floppy disk for reading on another machine. Place an MSDOS formatted floppy in your disk drive and execute the following commands:
• mount -t msdos /dev/fd0a /mnt
• dmesg >/mnt/dmesg.txt
• umount /mnt
If you have another OpenBSD system, you can also write it to an OpenBSD compatible floppy -- often, the boot floppy has enough room on it to hold the dmesg. In that case, leave off the "-t msdos" above.
• Serial Console: Using a serial console and capturing the output on another computer is often the best way to capture diagnostic information - particularly if the computer panics immediately after boot. As well as a second computer, you will need a suitable serial cable (often a null-modem cable), and a terminal emulator program that can capture screen output to file.
General information on setting up a serial console is provided elsewhere in the FAQ; in order to capture a log of the install, the following commands are usually sufficient.
i386
At the boot loader prompt, enter
boot> set tty com0
This will tell OpenBSD to use the first serial port (often called COM1 or COMA in PC documentation) as a serial console. The default baud rate is 9600.
Sparc/Sparc64
These machines will automatically use a serial console if started without a keyboard present. If you have a keyboard and monitor attached, you can still force the system to use a serial console with the following invocation at the ok prompt.
ok setenv input-device ttya
ok setenv output-device ttya
ok reset
• FTP: Under some circumstances, and provided you first set up the network correctly, you may be able to use the ftp(1) client on the boot disk or CD-ROM to send the dmesg to a local FTP server, where you can retrieve it later.

source : www.openbsd.org