I initially thought the 'whereis' command searched all directories so it may have been tclConfig.sh existed under tcl8.6 and installing tcl8.6-dev was unnecessary. My problems were also compounded by the fact I was accessing ubuntu via win10 WSL. It took days of investigation and a thread on git hub to find out that WSL wasn't picking up on changes to the PATH in /etc/environment and that any changes had to be made in the /etc/profile.d/myenvvars.sh file. I had to create the latter file and add export PATH=~/sqlite:/usr/lib/tcl8.6:$PATH and reboot WSL to get those directories on the PATH. Edit: Going by https://packages.ubuntu.com/ tcl8.6 doesn't have the tclConfig.sh and tcl8.6-dev is needed.