Managing Running Processes
In addition to being a multiuser operating system, Linux is also a multitasking system. Multitasking means that many programs can be running at the same time. An instance of a running program is referred to as a process. Linux provides tools for listing running processes, monitoring system usage, and stopping (or killing) processes when necessary.
From a shell, you can launch processes, and then pause, stop, or kill them. You can also put them in the background and bring them to the foreground. This chapter describes tools such as ps, top, kill, jobs, and other commands for listing and managing processes.
A process is a running instance of a command. For example, there may be one vi command on the system. But if vi is currently being run by 15 different users, that command will be represented by 15 different running processes.
A process is identified on the system by what is referred to as a process ID. That process ID is unique for the current system. In other words, no other process can use that number as its process ID while that first process is still running. However, once a process is ended, another process can reuse that number.
Along with a process ID number, there are other attributes associated with a process. Each process, when it is run, is associated with a particular user account and group ...