Mac OS X Leopard - ARCAism

302
CHAPTER 18 INTRODUCING DARWIN AND THE SHELL
who
And all our yesterdays have lighted fools
The way to dusty death. Out, out, brief candle!
Life's but a walking shadow, a poor player
That struts and frets his hour upon the stage
And then is heard no more: it is a tale
Told by an idiot, full of sound and fury,
Signifying nothing.
The who command tells you who else is logged in to the computer. Traditionally, this would just
be you, since most personal computers would only allow one person to be logged in at a time
(and this is how we still tend to use them). However, if you’ve turned on the Remote Login
option in the Sharing control pane, it’s possible for multiple users to actually be using one Mac
OS system at a time. who also has a related command, whoami, which will also tell you your username
if you ever forget. (By the way, your Darwin username is the “short” username you pick
when you create your account.)
To see these in action on your system isn’t always that exciting:
ps
Leopard:~ scott$ who
scott console May 20 19:39
scott ttyp1 May 20 20:17
Leopard:~ scott$ whoami
scott
NOTE who may be considered dangerous by many systems administrators who feel it’s a
potential security breach to disclose too much information about the system or its users; for
this reason, on many of today’s servers, systems are in place to keep you from finding out
who’s really online at any time. Of course, the real cool (or if you’re a systems administrator,
real bad) command that is similar to who is finger. Traditionally, finger would allow you to find
out all sorts of personal information about any user, not only those on your local machine, but
you could actually “finger” anyone on any UNIX-type machine (and most other multiuser systems
of the day). The finger command still exists on some computers and is even installed on
your Mac (go ahead try it)—however, it’s unlikely that you’ll be able to find many machines on
your network or on the Internet that will allow you to finger them or any of their users (for
aforementioned security and even privacy fears). By default, Leopard will not allow any remote
machine to finger you.
ps allows you to view what processes are running at any given time on your system. By default,
it shows limited information about all the services running from the terminal you are using (i.e.,
only the current Darwin process that you’ve started from your current terminal session). Until
you really start digging into the power of Darwin, ps will likely just return your shell as your
only process:
Leopard:~ scott$ ps
PID TTY TIME CMD
310 p1 0:00.12 -bash
The important pieces of information here are the PID (process ID) and the COMMAND. However,
with a few options, ps can give you lots of information about every command running on your
system. The most common options are -a, -u, and -x (so common, in fact, that you can issue
them without the -). This will most likely give you a long scrolling list of processes: