In GNS3 Workbench 12.3, there is a slight misconfiguration with VPCS out of the box. When you are in an exercise and try to launch VPCS via Tools > VPCS multi-host, you get an error stating "VPCS program '/home/user/vpcs' is not accessible".
Fortunately, this is an easy fix. The issue is that GNS3 has the wrong path to VPCS specified.
To get the correct path, open a terminal and run the which vpcs command. Running this command indicates that the correct VPCS path is /usr/bin/vpcs.
Now go to Edit > Preferences, and go to the VPCS section. Update Path to VPCS: with the correct path and click OK.
|Update Path to VPCS: with the correct path.|
After doing this, you should be able to launch VPCS without any issues.