Linux process states

A linux process is in one of the following states:

• (R)unning or runnable (on the run queue)
• (U)ninterruptible sleep (waiting for some event)
• (I)nterruptible sleep (waiting for an event or or a signal)
• (S)topped (either by job control signal or because of being traced by a debugger)
• (Z)ombie process (terminated, but not reaped by parent process)

ps -l shows the state of a process in the first character of the STAT column. There are also optional attributes such as s for a session leader or + if the process is part of a foreground process group.

Additionally, the WCHAN (wait channel) column shows which kernel event a sleeping process is waiting for.