The command kill sends the specified signal to the specified process or process group. If no signal is specified, the TERM signal is sent. The TERM signal will kill processes which do not catch this signal. For other processes, it may be necessary to use the KILL signal, since this signal cannot be caught.
Most modern shells have a builtin kill function, with a usage rather similar to that of the command described here. The "-a" and "-p" options, and the possibility to specify pids by command name is a local extension.
If sig is 0, then no signal is sent, but error checking is still performed.
kill [OPTION] [--] pid...
pid... Specify the list of processes that kill should signal. Each pid can be one of five things:
n where n is larger than 0. The process with pid n will be signaled.
0 All processes in the current process group are signaled.
-1 All processes with pid larger than 1 will be signaled.
-n where n is larger than 1. All processes in process group n are signaled. When an argument of the form "-n" is given, and it is meant to denote a process group, either the signal must
be specified first, or the argument must be preceded by a "--" option, otherwise it will be taken as the signal to send.
commandname All processes invoked using that name will be signaled.
-s signal Specify the signal to send. The signal may be given as a signal name or number.
-l Print a list of signal names. These are found in /usr/include/linux/signal.h
-a Do not restrict the commandname-to-pid conversion to processes with the same uid as the present process.
-p Specify that kill should only print the process id (pid) of the named processes, and not send any signals.
The command kill sends signals to currently active processes. It requires a process number (process ID, or PID) as an argument. This PID can been seen using ps.
If the corresponding process fails to catch the signal, it can be killed by giving the optional parameter -9.
[root@server1 ~]# kill -9 <pid>