This manual gives a basic introduction to the UNIX operating system
(OS), in particular, system administration. Although this manual should be
helpful for any type of UNIX OS, it has been written for Silicon Graphics
Inc. (SGI) IRIX, versions 5.3 or 6.5, which is a UNIX OS. It is not
intended as an in depth guide to any particular aspect of the system.
Copious information on every topic covered here (as well as many more) can
be found in the IRIX on-line help manuals (see Getting Help,
below).
Conventions
Convention in this manual is
driven by the desire to provide an easy to use reference document.
Overall, words that directly refer to commands and occasionally concepts
in UNIX are provided in the
courier font. This is true of
command syntax listings, specific keystrokes, examples, file names, and
filesystem paths. Specific keystrokes are designated by enclosure in
brackets (e.g. <esc>, for the escape character, <b> for the b key).
Commands referenced in the text are given as a syntax listing following
the paragraph or section, the exception being made up commands which are
given as examples. Command syntax listings are indented from body text and
give the generic command syntax in bold with variable arguments or
options enclosed in brackets. If appropriate, the generic form is followed
by an example of command usage in bold italic font. A
generic example is shown below.
command [type of
argument(s)]
--- generic
form
command argument
example(s)
---
specific example
Explanation …--- explanation of usage
UNIX Organization
The UNIX OS is based on a multiple-user framework. Many UNIX
servers have hundreds if not thousands of individual users. For this
reason it is essential that users do not have complete access to the
system. This is accomplished by giving each user their own private account
with a password and access privileges (reading and writing files) to a
small portion of the system, their home directory. In general, many areas
of the system are open to the user for reading files, but relatively few
are open for writing files. This means that multiple users can have access
to programs and information stored in the system but can’t destroy it
or clutter it up. The exception to this rule is the system administrator,
referred to as
root or the super-user, and is discussed below (UNIX Administration).
Most ‘modern’ UNIX systems have multiple levels of user
interaction. At the base is the UNIX kernel, although, in general, even
the advanced user will not directly interact with this level of UNIX. The
most basic way of accessing the UNIX kernel is by using a shell, which is
a command line interpreter. A shell is used from a text-based window,
either on the computer itself or from a remote location. The user types in
commands with arguments and options (the input to the command) and the
command performs the given function and returns output.
A separate way of accessing the kernel is through a GUI. Most
GUI’s overlay or are based on X-windows, a relatively standard
framework for UNIX GUI’s. The IRIX GUI is an icon-based desktop-type
interface which is very similar to Macintosh or Windows type interfaces.
Since it is intuitive and easy to use, basic operation of the GUI will not
be discussed here. A feature of the IRIX GUI worth noting at this point,
is the
toolchest.
The toolchest is
a small window which has several menus with useful features for users,
administrators and for finding help with topics.
UNIX Administration
The system administrator(s) must be able to perform tasks relating to
the basic operation of the system. This is achieved through a special user
account (
root)
which allows all access privileges to all areas of the system. Anyone
logged in as root
has these privileges, so it is essential that only a few users, at most,
have this password. It should not be given out as a temporary solution to
a particular user’s need for access to a particular region of the
computer or for any other reason except to assume regular performance of
administrative tasks. At risk of sounding paranoid it is essential that
the password not fall into the wrong hands (i.e. anyone else but the
system administrator) and steps should be taken to ensure that it does
not. For instance, don’t write the password down, don’t type it
in with someone looking over your shoulder and don’t give it out to
anyone. A user with the root password has absolute control over the system and could
really muck things up (e.g. quite easily erase all the information on the
computer), even without meaning to. To use the root account either log in
under the root account from the SGI login screen or use the su command from any shell as
described below.
Basic system administration for the IRIX OS is really quite simple. All
of the standard tasks performed by UNIX administrators has been given a
GUI in IRIX. This makes complex tasks quick and simple to perform but
tends to mask the real workings of the system. With a few exceptions, this
manual deals with the GUI level of UNIX administration and does not delve
into the confusing world of ‘real’, command-line UNIX
administration. It is worth noting that the
toolchest allows access to
most of the system administration functions via the System menu.
su [user]
su mcdermoj
Allows the current user to
switch user accounts to the specified user account. The
command will prompt for a password before continuing.
su
su —
Allows the current user to switch
accounts to the
root account and become a super-user. Including
the dash option will open the root’s shell which may make some
operations easier.
whoami
Returns the name of the user
account currently being used.
Getting Help
Under SGI IRIX several useful help features are available. Most
GUI-based programs have some kind of help feature or menu built in. The
toolchest
Help menu allows
access to manual pages as well as a large library of books, several of
which deal with system administration.