User1 is attempting to assist user2 with terminating user2's process 1234.

Kill -9

Kill (terminates without cleanup)

Only works if issued by process owner or super user (root)

The program cannot respond to this signal; it must terminate

Note: Unix provides security mechanisms to prevent unauthorized users from killing other processes. Essentially, for a process to send a signal to another, the owner of the signaling process must be the same as the owner of the receiving process or be the superuser.