VMWare 15 Error on Ubuntu 18.4 - Could not open /dev/vmmon: No such file or directory

Accepted answer is ok but doing it a little better formatted and reordered steps, added expected feedback etc. The OP has some info for VirtualBox which gives confusing errors if you don't have it.

This problem essentially happens because of secure boot which does not allow kernel modules to load without being digitally signed with a trusted certificate. So we need to create a trusted key and use it to sign the newly compiled modules vmmon and vmnet.

These instructions have been tested for VMWare 15 and Ubuntu 18.04 up to 19.04.

1. Install VMWare

2. Run this

   sudo vmware-modconfig --console --install-all
   

   You'll see that there are issues with monitor and net, thas ok.

3. Generate a key

   openssl req -new -x509 -newkey rsa:2048 -keyout VMWARE15.priv -outform DER -out VMWARE15.der -nodes -days 36500 -subj "/CN=VMWARE/"
   

   You'll see info that it did it ok.

4. Use this key we just generated to sign the two kernel modules.

   sudo /usr/src/linux-headers-$(uname -r)/scripts/sign-file sha256 ./VMWARE15.priv ./VMWARE15.der $(modinfo -n vmmon)
   sudo /usr/src/linux-headers-$(uname -r)/scripts/sign-file sha256 ./VMWARE15.priv ./VMWARE15.der $(modinfo -n vmnet)
   

   This does not give any feedback

5. Check that signatures are applied correctly.

   tail $(modinfo -n vmmon) | grep "Module signature appended"
   

   You should get Binary file (standard input) matches

6. Now we make this key trusted by importing it to machine owner key (MOK) management system with the command below. Here you can read more about MOK’s job in Linux.

   sudo mokutil --import VMWARE15.der
   

   This will ask you for a password, enter some new password a bit long like 1515vmware. Reenter same password.

7. Reboot, When reboot you should be presented with a menu with blue screen background, you have to make your way to enroll the key and enter the password you just created, this happens only once, then continue to boot.

8. To test the driver / module installed correctly enter the command

   mokutil --test-key VMWARE15.der
   

   You should get VMWARE15.der is already enrolled and that means VMWare should be working.

All credits to OP.

Notice: I've found out that after some Linux updates which involves the kernel (or something like that) this fix stops working and you have to do all the steps again to get it working again. (No need to re-install vmware)

Problem solved! I followed the same exact steps in my original post EXCEPT that I changed the name of the key to something else! The new key successfully signed vmmon in dev directory and vmware worked!

I have made a simple bash script to make a small amount of automation to the process. It seems to be a recurring problem when patching Ubuntu and I find my self Googling for the solution everytime.

cd /tmp
wget https://raw.githubusercontent.com/rune1979/ubuntu-vmmon-vmware-bash/master/wm_autoupdate_key.sh
chmod +x wm_autoupdate_key.sh
./wm_autoupdate_key.sh

You can also find it in my github repo (https://github.com/rune1979/ubuntu-vmmon-vmware-bash)