May 16, 2025

Sun 3/280 - running rarpd on my linux machine

I just finished several hours of work moving the Sun 3/280. It is now in another room where I don't have to listen to the fans. It is also on the network for the first time. Ever at this house.

I am getting to the serial console via a network to usb to serial relay using a derelict Raspberry Pi.

General overview and upfront advice

The general flow of Sun3 diskless booting is as follows: Here are two tips upfront: The filename C0A8001E is the IP address the machine will use turned into hex. In my case I will use the IP address 192.168.0.30 and this is C0A8001E when turned into hex, you may of course need to use a different name.

For some stupid reason the people who designed rarpd made it check for a file with such a name in the /tftpboot directory. This violates the principle of having a program do one thing well and simply and introduces a needless interdependence. A bad decision we are now stuck with.

This bad decision is compounded by Fedora making the tftpd program work from the /var/lib/tftpboot directory by default (what was wrong with /tftpboot?) This change is no big deal (once you know about it), but it would only make sense to also make rarpd look into this directory. My tips are probably the simplest way to deal with all of this.

Note that if you just want to get this working, you can make C0A8001E be any rubbish file (for now). The rom will load and try to run it, but you can get this process set up and tested and then worry about proper content.

Getting started

I now see this: 
EEPROM: Using RS232 A port.
Selftest Completed.

Sun Workstation, Model Sun-3/200 Series.
ROM Rev 3.0, 16MB memory installed, Serial #13355.
Ethernet address 8:0:20:0:4:B1, Host ID 1300342B.


Testing 8 Megabytes of Memory ... Completed.

Auto-boot in progress...

EEPROM boot device...Boot: ie(0,0,0)
Requesting Internet address for 8:0:20:0:4:B1
The last message indicates that it is trying to get an IP number for itself using the ancient RARP protocol.

Installing and running rarpd on linux

I run Fedora 41 (the latest at this time). I see in the packages that rarpd is available, somewhat to my surprise. So: 
su
dnf -y install rarpd
That took all of 10 seconds. This expects a file /etc/ethers with a simple format: 
08:00:20:00:04:B1		192.168.0.30
I also add this entry to /etc/hosts 
192.168.0.30    sunny
And now I try the usual sort of things to start the service: 
vi ethers
root@trona:/etc# systemctl start rarpd
root@trona:/etc# systemctl enable rarpd
Created symlink '/etc/systemd/system/multi-user.target.wants/rarpd.service' → '/usr/lib/systemd/system/rarpd.service'.
And I see: 
ps -alx | grep rarp
1     0  185771       1  20   0   2560  1532 do_pol Ss   ?          0:00 /usr/sbin/rarpd

Firewall rules for rarpd

You don't need any!

The rarp protocol does not use any UDP or TCP port. It works at the data link level. So firewall rules are not involved. I test this by stopping the firewall and then pressing the reset button on the sun 3/280. It still does not work. 

systemctl stop firewalld
I try running wireshark with the capture filter "rarp". This works! I see the Sun sending "who is" packets, and wireshark even associates them with the proper IP -- 192.168.0.30!!

The problem (I discover later) is that rarpd is looking for a proper file in /tftpboot, not finding it, and refusing to respond.

Running rarpd with the "-e" switch

There is a man page for rarpd, and it talks about the default behavior being not to respond if there is not a bootable image in the /tftpboot directory. I decide to run rarpd by hand and give it some options: 

systemctl stop rarpd
cd /usr/sbin
./rarpd -v -e
I should also have given the -d switch to get it to stay at the terminal. However with the -e switch (telling it not to check for a bootable image) it works: 
EEPROM boot device...Boot: ie(0,0,0)
Requesting Internet address for 8:0:20:0:4:B1
Using IP Address 192.168.0.30 = C0A8001E
tftp: time-out.

On to tftp -- see a separate page on sorting this out

And now it is on to tftp, trying to get some file. I have a strong hunch based on old memories, but I run wireshark with capture filter "port tftp" to see what I can learn. And I am right, it is trying to read a file with the name C0A8001E, which is the ip address in hex. So, let's give it one!

Fedora runs tftpd using the directory /var/lib/tftpboot. Let's see what happens if I do this: 

cd /var/lib/tftpboot
cp /etc/hosts C0A8001E
And to check the obvious: 
ps -alx | grep tftp
4     0  187297       1  20   0   2836  1788 do_sel Ss   ?          0:00 /usr/sbin/in.tftpd -s /var/lib/tftpboot
Wireshark shows that requests keep being sent to read this file, but my tftp server is not responding.
I try this: 
systemctl restart tftp.service
Nope.

I am starting a new page just for tftp setup.

Note that the "right thing" to do is to have the proper file waiting in the tftp directory (but rarpd must know what directory that is). So you don't really need to run it with the -e switch, just have the file ready.

Make the -e thing permanent

I did the following, but making the /tftpboot symlink as I recommend up top is a better solution I think.

I rebooted, and the sun fails to get a rarpd response. I am sure this is because rarpd is looking at the old /tftpboot location. I wish the -e switch behavior was the default.

We start this via "systemctl start rarp.service" -- two files may be significant: 

/etc/systemd/system/multi-user.target.wants/rarpd.service
/usr/lib/systemd/system/rarpd.service
But why two? And which one? The word is that the stuff in /etc is for customizations and the stuff in /usr/lib is the base standard and should not be fooled with. The recommended process is to use "systemctl edit rarpd.service" and add a "snippet".

This would generate /etc/systemd/system/rarpd.service.d/override.conf

This is all well and good, but just what do I put in here to add the -e option to rarpd? 

ExecStart=
ExecStart=/usr/sbin/rarpd -e $OPTIONS $INTERFACE
After some searching, I used systemctl edit and typed in the above. When I exit their crazy editor I see: 
Successfully installed edited file '/etc/systemd/system/rarpd.service.d/override.conf'.
I restart the service, press reset on the sun, but it does not work.

Get ugly

I edit the file I am not supposed to edit, namely: 
/usr/lib/systemd/system/rarpd.service
I add the "-e" option as follows: 
ExecStart=/usr/sbin/rarpd -e $OPTIONS $INTERFACE
Then I do: 
systemctl daemon-reload
systemctl restart rarpd.service
And it works! So much for this fancy (but useless) systemctl edit business.

Yet, I may have to revisit this someday when and if someone updates rarpd, but I have these notes to help me then.

Much more of this and I'll just go find rarpd source, build and run it myself. Then I can make it look in /var/lib or just make -e the default.

Feedback? Questions? Drop me a line!

Tom's Computer Info / tom@mmto.org