Quote:

I tried to do the measures without the strontium source, but the Alibava didn't cooperate with me. First, it wasn't catching any events, then, I tried to put the Trigger on -20 and on -10. Nothing either.. Second, when I tried to restart the Alibava, it didn't open anymore. I used the comand sudo chmod a+rw/dev/ttyUSB0 and didn't work.. This message appeared: chmod: missing operand after ‘a+rw/dev/ttyUSB0’                                       Try 'chmod --help' for more information. Then, I give up.

 the command is wrong.  it told you: missing operand. it means it misses an argument

you miss a space:

sudo chmod a+rw                                        /dev/ttyUSB0

copy and paste the command above.