Tutorial Seven: UNIX Tutorials


UNIX Tutorial Seven

7.1 Compiling UNIX software packages

We have many public domain and commercial software packages installed on our
systems, which are available to all users. However, students are allowed to
download and install small software packages in their own home directory, software
usually only useful to them personally.

There are a number of steps needed to install the software.

  • Locate and download the source code (which is usually compressed)
  • Unpack the source code
  • Compile the code
  • Install the resulting executable
  • Set paths to the installation directory

Of the above steps, probably the most difficult is the compilation stage.

Compiling Source Code

All high-level language code must be converted into a form the computer understands.
For example, C language source code is converted into a lower-level language
called assembly language. The assembly language code made by the previous stage
is then converted into object code which are fragments of code which the computer
understands directly. The final stage in compiling a program involves linking
the object code to code libraries which contain certain built-in functions.
This final stage produces an executable program.

To do all these steps by hand is complicated and beyond the capability of the
ordinary user. A number of utilities and tools have been developed for programmers
and end-users to simplify these steps.

make and the Makefile

The make command allows programmers to manage large programs or
groups of programs. It aids in developing large programs by keeping track of
which portions of the entire program have been changed, compiling only those
parts of the program which have changed since the last compile.

The make program gets its set of compile rules from a text file
called Makefile which resides in the same directory as the
source files. It contains information on how to compile the software, e.g. the
optimisation level, whether to include debugging info in the executable. It
also contains information on where to install the finished compiled binaries
(executables), manual pages, data files, dependent library files, configuration
files, etc.

Some packages require you to edit the Makefile by hand to set the final installation
directory and any other parameters. However, many packages are now being distributed
with the GNU configure utility.

configure

As the number of UNIX variants increased, it became harder to write programs
which could run on all variants. Developers frequently did not have access to
every system, and the characteristics of some systems changed from version to
version. The GNU configure and build system simplifies the building of programs
distributed as source code. All programs are built using a simple, standardised,
two step process. The program builder need not install any special tools in
order to build the program.

The configure shell script attempts to guess correct values for
various system-dependent variables used during compilation. It uses those values
to create a Makefile in each directory of the package.

The simplest way to compile a package is:

  1. cd to the directory containing the package’s source code.
  2. Type ./configure to configure the package for your system.
  3. Type make to compile the package.
  4. Optionally, type make check to run any self-tests that come
    with the package.
  5. Type make install to install the programs and any data files
    and documentation.
  6. Optionally, type make clean to remove the program binaries
    and object files from the source code directory

The configure utility supports a wide variety of options. You can usually use
the –help option to get a list of interesting options for a particular
configure script.

The only generic options you are likely to use are the –prefix
and –exec-prefix options. These options are used to specify the
installation directories.

The directory named by the –prefix option will hold machine independent
files such as documentation, data and configuration files.

The directory named by the –exec-prefix option, (which is normally
a subdirectory of the –prefix directory), will hold machine dependent files
such as executables.

7.2 Downloading source code

For this example, we will download a piece of free software that converts between
different units of measurements.

First create a download directory

% mkdir download

Download the software here and
save it to your new download directory.

7.3 Extracting the source code

Go into your download directory and list the contents.

% cd download

% ls -l

As you can see, the filename ends in tar.gz. The tar command turns
several files and directories into one single tar file. This is then compressed
using the gzip command (to create a tar.gz file).

First unzip the file using the gunzip command. This will create
a .tar file.

% gunzip units-1.74.tar.gz

Then extract the contents of the tar file.

% tar -xvf units-1.74.tar

Again, list the contents of the download directory, then go
to the units-1.74 sub-directory.

% cd units-1.74

7.4 Configuring and creating the Makefile

The first thing to do is carefully read the README and INSTALL
text files (use the less command). These contain important information
on how to compile and run the software.

The units package uses the GNU configure system to compile the source code.
We will need to specify the installation directory, since the default will be
the main system area which you will not have write permissions for. We need
to create an install directory in your home directory.

% mkdir ~/units174

Then run the configure utility setting the installation path to this.

% ./configure –prefix=$HOME/units174

NOTE:

The $HOME variable is an example of an environment variable.

The value of $HOME is the path to your home directory. Just
type

% echo $HOME

to show the contents of this variable. We will learn more about environment
variables in a later chapter.

If configure has run correctly, it will have created a Makefile with all necessary
options. You can view the Makefile if you wish (use the less command),
but do not edit the contents of this.

7.5 Building the package

Now you can go ahead and build the package by running the make
command.

% make

After a minute or two (depending on the speed of the computer), the executables
will be created. You can check to see everything compiled successfully by typing

% make check

If everything is okay, you can now install the package.

% make install

This will install the files into the ~/units174 directory
you created earlier.

7.6 Running the software

You are now ready to run the software (assuming everything worked).

% cd ~/units174

If you list the contents of the units directory, you will see a number of subdirectories.

bin The binary executables
info GNU info formatted documentation
man Man pages
share Shared data files

To run the program, change to the bin directory and type

% ./units

As an example, convert 6 feet to metres.

You have: 6 feet

You want: metres

* 1.8288

If you get the answer 1.8288, congratulations, it worked.

To view what units it can convert between, view the data file in the share
directory (the list is quite comprehensive).

To read the full documentation, change into the info directory
and type

% info –file=units.info

7.7 Stripping unnecessary code

When a piece of software is being developed, it is useful for the programmer
to include debugging information into the resulting executable. This way, if
there are problems encountered when running the executable, the programmer can
load the executable into a debugging software package and track down any software
bugs.

This is useful for the programmer, but unnecessary for the user. We can assume
that the package, once finished and available for download has already been
tested and debugged. However, when we compiled the software above, debugging
information was still compiled into the final executable. Since it is unlikey
that we are going to need this debugging information, we can strip it out of
the final executable. One of the advantages of this is a much smaller executable,
which should run slightly faster.

What we are going to do is look at the before and after size of the binary
file. First change into the bin directory of the units installation
directory.

% cd ~/units174/bin

% ls -l

As you can see, the file is over 100 kbytes in size. You can get more information
on the type of file by using the file command.

% file units

units: ELF 32-bit LSB executable, Intel 80386, version 1, dynamically
linked (uses shared libs), not stripped

To strip all the debug and line numbering information out of the binary file,
use the strip command

% strip units

% ls -l

As you can see, the file is now 36 kbytes – a third of its original size. Two
thirds of the binary file was debug code !!!

Check the file information again.

% file units

units: ELF 32-bit LSB executable, Intel 80386, version 1, dynamically
linked (uses shared libs), stripped

HINT: You can use the make command to install pre-stripped copies
of all the binary files when you install the package.

Instead of typing make install, simply type make install-strip

 

M.Stonebank@surrey.ac.uk, © October 2001

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