I use Linux Mint on one of my machines. The other day I tried xclock via Terminal command line. I then found I couldn't stop, end or kill it. Or rather I could kill it but it immediately restarted. Every time.
Since then it starts with every system startup, in the middle of the screen, in default colours. I can start a second instance, with any parameters I choose, and successfully kill the new one. But I can't get rid of the old one.
This is driving me mad. How can I remove whatever starts this thing every time?