The command has the following optional parameter.

 command-string

 	Specifies a command string of up to 131 characters that is to
 	be executed in the context of the created sub-process.

 	When the command completes, the sub-process terminates and
 	control returns to the parent process.

 	If you do not specify a command string, a sub-process is
 	created and remains until you log out.