Welcome to the ``tip of the week'', a pithy kickshaw provided on a
sometimes weekly basis.

This is a brief discussion of process management using the Unix
functions `ps' and `kill'.  

We stick to the basics below; for more information see the manual
pages (type ``man ps'' in any shell window).  Also, be warned that
details on the ps function vary between different dialects of Unix.

A ``process'' is a running program.  For example, you have a shell
process running any time that you are logged in to one of our
computers, and if you are sitting at a workstation with the window
system running then you have processes running to create and manage
the window system, along with xterm and shell processes, plus any
other applications you might have open such as clocks, calendars, and
mail readers.  The operating system takes care of the complicated job
of sharing computer time among many competing processes.

The issue of tracking and managing your own processes arises for a
couple of reasons.  You may have left a job running in background
using the ampersand(`&') directive; a dropped modem connection might
have left some garbage behind; or a running program might have become
unresponsive.

The `ps' command (think ``process status'') displays information about
processes, potentially listing all the processes running on a CPU for
any user.  The information available can be daunting, so ps has a large
number of flags to shape its report format.

  % ps

Without any flags, the ps command lists processes running with your
user ID and attached to a terminal.  (For these purposes, different
xterm windows count as distinct terminals.)

  % ps -x

The `x' flag directs ps to exhibit all the processes running under
your user ID, whether or not they are attached to a terminal.  If
you suspect that you have some leftover programs consuming resources
then this flag is appropriate.

Here is an example:

  % ps -x
    PID TT STAT  TIME COMMAND
    109 co IW    0:03 -tcsh (tcsh)
   2263 co IW    0:00 /bin/sh /math/x/startx
   2267 co IW    0:00 xinit /depot/X11R5/lib/X11/xinit/xinitrc.system
   2268 co S   120:37 /depot/X11R5/bin/XsunMono :0
   2269 co S     2:18 twm
   2281 p0 IW    0:37 xwalld
   2285 p1 S     0:19 -tcsh (tcsh)
   9071 p1 R     0:00 ps -x
  
This basic output format includes some status and location information
along with each process's identification number (PID).  Note that the
`ps' process itself appeared in the list.

Suppose you want to delete one of your processes, for example an
old chess game or ftp session that never closed out properly.  This
chore should be done with the `kill' command, which sends signals of
various kinds to processes, including signals which terminate most
running processes.

To kill a process, you need its process identification number from
the PID column of a ps report.  Many processes will shut down if
you simply type ``kill PID'', as in 

  % ps -x
    PID TT STAT  TIME COMMAND
  21529 p1 I     1:10 xbiff

  % kill 21529

-- if this does not work, then a nearly sure kill is possible with the
`-9' or `-KILL' flag:

  % kill -KILL 21529
	
You can't kill processes owned by other users and it is usually 
impossible to kill processes which have become `zombies', as indicated
by a ``Z'' in the status column of ps's output.  The superuser can
kill any of your processes, except zombies, so if you have trouble
with a runaway program please notify consult@math.ufl.edu.



Past Tips of the Week are found in /usr/local/tips.  They may be
consulted through the Documentation/Online Help menu item of the
window system's main menu or through Info mode in the Emacs editor.


						     cws@math.ufl.edu

Subject:	processes - ps and kill