Processes lie at the heart of all modern multiuser operating systems. By dividing system tasks into small, discrete elements that are uniquely identified by a process identifier (PID), Solaris is able to manage all the applications that may be concurrently executed by many different users. In addition, individual users may execute more than one application at any time. Each Solaris process is associated with a UID and a GID, just like a standard file. This means that only users may send signals to their own processes (except for the superuser, who may send signals to any process on the system). Signals are typically used to restart or terminate processes. The multiuser, multitasking process model in Solaris ensures that system resources can be shared equally among all competing processes or allocated preferentially to the most important applications. For example, a firewall application would probably take precedence over all other system processes. Individual users and the superuser may allocate a priority level to active processes in real time.
Solaris provides a number of command-line tools that can be used to manage processes. In addition, APIs are provided for C programmers to allow them to operate directly on processes—spawning, managing, and killing as necessary. Solaris also provides lightweight processes (LWPs) that don’t require as much overhead to operate as “normal” processes.