Learning Unix for Mac OS X, Second Edition

Checking on a Process

If a background process takes too long, or you change your mind and want to stop a process, you can check the status of the process and even cancel it.

ps

When you enter the command ps, you can see how long a process has been running, the process ID of the background process, and the terminal from which it was run. The tty program shows the name of the Terminal where it’s running; this is especially helpful when you’re logged into multiple terminals, as the following code shows:

% ps
  PID  TT  STAT      TIME COMMAND
  310 std  S      0:00.37 -tcsh (tcsh)
  510 std  R+     0:00.00 ps
  459  p2  S+     0:00.25 -tcsh (tcsh)
% tty
/dev/ttyp1

std corresponds to your current Terminal window, and p2 corresponds to the Terminal window for ttyp2. In its basic form, ps lists the following:

Process ID (PID)

A unique number assigned by Unix to the process.

Terminal name (TT)

The Unix name for the terminal from which the process was started.

Run time state (STAT)

The current state of each job. S is sleeping, R is runnable, T is stopped, and I is idle (sleeping for more than 20-30 seconds). Additionally, the state can include + to indicate it’s part of the foreground group process, E to indicate the process is exiting, and W to mean it’s swapped out.^[12]

Run time (TIME)

The amount of computer time (in minutes and seconds) that the process has used.

COMMAND

The name of the process.

Each terminal window has its own terminal name. The previous code shows processes running on two windows: std ...