Classic Mac OS debugging output

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Revision as of 04:35, 26 September 2025 by Huntertur (talk | contribs) (Change example IP)
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You can make the Classic Mac OS dump a bunch of debugging output to Open Firmware during boot and sometimes the screen after boot.

To do this, open Open Firmware during boot with Command-Option-O-F and enter dev / 3013FFF encode-int " AAPL,debug" property. Then, boot with mac-boot.

If you want a log of this output, you should hook your machine up to the local network, then run this, replacing the IP address with whatever is available for the machine to use: 

dev /packages/telnet
" enet:telnet,192.168.18.10" io

Then connect to your machine via Telnet before booting.

Notes

  • This does not work on a tray-loading iMac G3 because /packages/telnet does not exist.
  • The screen will become blank after connecting from the client machine.
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