How can I stop a running R command in linux other than with Ctrl + C?

I have had the problem you mention. Ctrl + C will work when R is able to realize "Oh, this guy/gal wants me to stop running that particular command." However, often R cannot do that. So you have to run Ctrl + \ (note that it's a backslash, not a forward slash). This tells Linux "Hey, R is not listening to me, can you stop running R?".

Try Ctrl + C first, because if it works you will still have your R session. If it doesn't work, and you do Ctrl + \ you will lose your R session, but at least it stops the process.

If that doesn't work either, then I would suggest a killall R or a kill -9 [PID] where you find the PID by running pus aux.

Try to use Ctrl + C, pause R with Ctrl + Z, and then unpause R with fg (#job).

I tried the solutions given in previous answers with sending some signals to R with kill, but neither worked. Then I tried the sequence above (Ctrl + C, Ctrl + Z, and fg 1) and it worked. I could continue the R session.

I'm not sure whether it was one of the signals or Ctrl + C that stopped R, but I guess Ctrl + Z was essential here.

You can also try

kill -USR1 [pid]

This will interrupt some R calls and sometimes give you the option to save and quit rather killing the process altogether.