Best version for Parport machine and how to install

Hey guys,

I first installed Linuxcnc 2.7 a few years ago just to have a look at it. Recently I finished the mechanics of my machine, which has dual Y steppers.
I found a good tutorial to add the second stepper in the HAL and INI, but I found out that 2.7 is quite old and the method described in the tutorial wouldn't work. I decided to do a fresh install of 2.9 per download page (LinuxCNC 2.9.3 Debian 12 Bookworm PREEMPT-RT ISO).

I did a latency test and got terrible results (120000ns while I got 15000ns on the previous install of 2.7). From what I can gather, this is due to the PREEMPT kernel. I can see a pinned post on the forum for "RTAI deb", but I have no idea how I would install this on my machine since it is not connected to the internet.

As you may be able to tell, I'm a bit out of my depth here. What I'm looking for is idiotproof instructions on how I can get 2.9 with the RTAI kernel on my PC, preferrably in a way that is as simple as installing the ISO.

Hope you guys can help.

You can put the .deb files on a flash drive and install them as you usually would with `sudo dpkg -i <all .deb files go here>`

For example:

1.) Download all the .debs from this sticky:

forum.linuxcnc.org/9-installing-linuxcnc...ng-rtai-debs-for-2-9 (the 5.4.279 ones)

2.) Put them on a flash drive on one machine that has access to the internet (any machine, doesn't need LinuxCNC)

3.) On the LinuxCNC machine, run:

4.) Now plug the flash drive into your LinuxCNC machine that doesn't have internet access

5.) Make a directory in your home folder (/home/<your user>) called RTAI on the LinuxCNC machine

6.) Use the graphical file manager to copy the files off the flash drive into your newly created RTAI folder

7.) In a terminal, go to that directory:

8.) Run:

9.) Reboot and select the RTAI kernel via the GRUB menu (this is the menu that has a list of kernels you can choose from at boot. It launches right after the BIOS is done.)

10.) Run the latency test or latency histogram.

Thanks! You're a legend. Got it to work and the jitter dropped to about 12000ns.

I've tried to edit the grub file so it loads the RTAI kernel by default as a quality of life improvement. Unfortunitely, editing GRUB_DEFAULT didn't work because the kernal options are in the "advanced options" menu. I'd love to know how to get the system to boot using the RTAI kernal without having to intercept the GRUB menu every time.

In /etc/default/grub:

GRUB_DISABLE_SUBMENU=true

You will need to modify the file with superuser permissions, but if you're new to Linux, using vim or nano might be too tedious. You can use something like:
or:and then launch the graphical editor as a superuser like so:or:I'm not on Debian right now, so if gksudo doesn't work, try gksu, and if that doesn't work, then resort to using `sudo` instead. Common practice is to never use `sudo` though for graphical applications.  After modifying /etc/default/grub (there should be a comment already in the file about GRUB_DISABLE_SUBMENU) run:Now count the number of menuentries starting from 0, then make that your `set default=` setting. Afterward, re-run:command again.

Looks like gksudo and the likes have been removed from Debian and Ubuntu.

One thing you could do:

And then modify the file without escalated privileges in any editor of your liking, then cat the file back:

Awesome, that did the job!

Yay, I helped someone!

andypugh wrote:

You can select from submenus, but the format isn't well documented and it might take some experimentation to figure out which menu and submenu are which number.
I have:

GRUB_DEFAULT="4>2"

 

Heh! I never knew!