Setting Linux AX.25 parameters
Setting things like paclen, maxframe, and the retry timer under Linux require setting a variable in the /proc/sys/net/ax25/<interface name> pseudo-directory; this directory contains a bunch of things that look like files, but they're not -- they are a user-accessible interface into various kernel values. Unfortunately, those settings aren't preserved on reboot, so you need a way to set them every time you start your AX.25 system.
You could do something simple, like echoing the value you want into the file, but I wrote a couple of simple scripts that do the trick. While we're on the subject, I also tweaked on a script that Jonathan Naylor wrote to display the current values of the paramters.
axgetparms
The axgetparms script reads the values of the files in /proc/sys/net/ax25/<interface name> (there's one directory in there for each interface) and copies them into a set of directories under /etc/ax25/parms. This creates a set of editable files that mirror the contents of the kernel variables at the time they are created. You only need to run axgetparms once, or if you add a new AX.25 device.
Now that you've created the files in /etc/ax25/parms, you can edit them to set the parameters you want. For example, to change the paclen value for device ax0 to 192 (though I'm not sure why you'd want to...), you would open the file /etc/ax25/parms/ax0/maximum_packet_lengthi in your favorite editor and change its one line of contents to read "192".
axsetparms
The axsetparms script reads the values from /etc/ax25/parms and "copies" them into /proc/sys/net/ax25/<interface name>. By running this script at boot time, you can update the kernel parameters to match the values contained in /etc/ax25/parms.
axdispparms
Finally, the axdispparms script reads the values of /proc/sys/net/ax25/ and displays them for you. Jonathan Naylor wrote the original script, and I just did a little bit of updating to clean up a couple of things.