Commands and options
UNIX commands take the form of a name (such as
date), possibly followed by options,
and other arguments as required. An option is
denoted by a hyphen (-) followed by a single character
(itself possibly followed by arguments). For example, the command
date can take only one possible option, namely
-u. Without this option, the date and time are printed
for the local timezone; with option -u the time is
converted to UTC (Universal Coordinated time,
essentially the same as GMT) thus
$ date -u
Tue Dec 4 20:10:39 UTC 2001
Information about exactly what machine and operating system
version is being used can be found by typing uname
(UNIX name). This command will either give a brief (one word)
description (typically the name of the operating system), or more
detailed information. uname allows several options,
including -a (all) to display all information about
the system. Note that a company which writes a UNIX operating
system will have its own name for it, and will update it
periodically; major updates are called releases,
minor updates are versions. For instance,
$ uname
Linux
$ uname -a
Linux box 2.4.10-4GB #1 Fri Sep 28 17:19:49 GMT 2001 i686
unknown
The output from uname indicates that the operating
system is Linux, its (kernel) release is
2.4.10, version #1 Fri Sep 28
17:19:49 GMT 2001, and the name of the machine you are using
is box. The hardware being used (i.e. the type of
physical machine, as opposed to the operating system, which is
software), is an i686. Options -m
(machine), -n (nodename), -r (release),
-s (system name) or -v (version) can be
used to print out part of the information that
-a (all) supplies. With no argument, -s
is assumed by default. You can combine options, for instance to
print out the release and version of your system, and can
do so in one of four ways:
$ uname -r
-v
2.4.10-4GB #1 Fri Sep 28 17:19:49 GMT 2001
$ uname -v -r
2.4.10-4GB #1 Fri Sep 28 17:19:49 GMT 2001
$ uname -rv
2.4.10-4GB #1 Fri Sep 28 17:19:49 GMT 2001
$ uname -vr
Try entering uname with the various options. You
will be communicating with the machine from a
terminal. The command tty displays
the name of the terminal you are currently using. If you are using
a windowed display, UNIX treats each window as a
separate terminal with its own name.
Worked Example
What is the name of the terminal or window you are using?
Solution: Use
tty:
$ tty
pts/1
and the name is pts/1 (or whatever is printed on
the screen by tty).
Note that some systems, including Sun's Solaris, have
more complex names, such as /dev/pts/1
Another command you can try now is who:
$ who
chris
pts/1 Dec 3 14:23 (console)
sam
ttyp2 Dec 3 08:38 (console)
jo
pts/4 Dec 3 13:58 (console)
This command lists those people currently logged in to the
system by username, together with the terminals
they are using and the dates and times they last logged in. On some
systems who will also display extra information. In
the above example chris logged in at 2.23 pm on Dec 3
to a terminal known as pts/1. This command allows
several options, including -u (unused); try typing the
command who -u. The output you will get is similar to
that for who on its own, except that an extra column
of information is given, perhaps:
$ who -u
chris pts/1 Dec 3 14:23 . (console)
sam ttyp2 Dec 3 08:38 01:03 (console)
jo pts/4 Dec 3 13:58 00:02 (console)
The extra column indicates idle time - the
amount of time a user has not touched the keyboard. So,
chris is active at the present moment (a dot is used
in place of a time if the user has actually used the system in the
previous few seconds). However, sam has been idle for
1 hour and 3 minutes (perhaps sam has forgotten to
logout?), and jo has been idle for only two minutes
(perhaps thinking about what to do next).
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