how to kill stubborn processes
 

I've used:

But that never seem to work. This usually revolves around copy operations, but not always.

I have search the web about this issue numerous times in the past, and I have never found an adequate solution. The only one being to simply reboot the computer.

Is there a better way? How would I see what operations are involved in the process and then kill -9 them?

If -9 won't kill it then it is probably already dead (aka a "zombie process"). The way to get those out of the process table is to kill the parent process that spawned it.

@hedron

Just adding, there is a rare level of "stubbornness" a process might turn into:
https://en.wikipedia.org/wiki/Sleep_...ruptible_sleep

Check the state of the process you want to kill with ps and if you get a Z - it's pretty much zombified, look after its parent. If it's D - well, send kill signals, wait, and if nothing happens use the "three-finger salute".
Here you can get an actual process state codes table:
https://unix.stackexchange.com/quest...-in-ps-command
or directly from the proc man page ( (3) state %c - section)
http://man7.org/linux/man-pages/man5/proc.5.html

kill -9 ( SIGKILL ) is really a last ditch attempt

you should try -2 ( SIGINT ) first ( that is what Ctrl+C sends )
if that fails -15 ( SIGTERM ), that asks the process to terminate

as @volkerdi points out, it is could be a zombie

https://en.wikipedia.org/wiki/Zombie_process

to figure out if it is a zombie, check ( top ) the status column is usually to the left of CPU% , look for Z ( PgDown/PgUp or Down/Up arrow )

As they are undead you cannot kill them, typically they are only around for a short time and are perfectly normal.
However, if you find a particular program/script often spawns "long lived" Zombies you should investigate and possibly discontinue use of it in favour of an earlier/later version that does not exhibit such bad behaviour.

for the most part they are harmless, as the zombie is not really doing anything ( although they may be hold onto resources )

some more details on signals ( man 7 signal )

SIGHUP ( -1 ) is worth a mention, you can use that to restart a process
I must admit, I don't think I've used that in quite a while a daemon is best restarted via init script/service


I have found some Python code to behave oddly ( notably git )
where I have had to send SIGINT ( -2 ) SIGTSTP ( -20 ) SIGCONT ( -18 ) for it to exit cleanly but I've not needed that in a long time.

Edit
Regards "copy operations" is this cp ?
If so I would investigate the health of the hard drive.