====== UNIX Tutorial Seven ======

===== 7.1 Compiling UNIX software packages  =====

Most unix systems have many public domain and occassionally commercial
software packages installed, which are available to all
users. However, you are allowed to download and install small software
packages in your own home directory, software usually only useful to
you 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 compilation.

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 optimization 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:

   - ''cd'' to the directory containing the package's source code.
   - Type ''./configure'' to configure the package for your system.
   - Type ''make'' to compile the package.
   - Optionally, type ''make check'' to run any self-tests that come with the package.
   - Type ''make install'' to install the programs and any data files and documentation.
   -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 Installing the development tools =====

Many Linux distributions will include a set of development tools
(i.e. the ''make'' tool and compilers). Unfortunately, the Ubuntu
Desktop Distribution -- which is designed for non-technical users --
does not! The development tools have to be installed separately, but
using the ''apt-get'' tool makes this relatively painless.

You will need to install the **build-essential** package which
includes the C-compiler ''gcc'', the ''make'' utility and essential
libraries. To install **build-essential** type 
<cli>ubuntu@ubuntu:~$ sudo apt-get install build-essential</cli>

Check that the essential tools have been installed as follows:
<cli>ubuntu@ubuntu:~$ gcc 

gcc: no input files

ubuntu@ubuntu:~$ make 

make: *** No targets specified and no makefile found. Stop.</cli>
Now you are ready to proceed. 

<note warning>You should be aware that, unless you have made your
settings persistent, you will need to repeat the above procedure
every-time you reboot from the Ubuntu live CD((Of course if you are by
now running from an installed Ubuntu system, your installation will be
permanent)).</note>
===== 7.3 Downloading source code =====

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

First create a **downloads** directory  
<cli>ubuntu@ubuntu:~$ mkdir downloads</cli>

Then click on this package file {{:eg-253:units-1.85.tar.gz|units-1.85.tar.gz}}
to save it to your new **downloads** directory.


===== 7.4 Extracting the source code  =====

Go into your **downloads** directory and list the contents. 
<cli>ubuntu@ubuntu:~$ cd downloads
ubuntu@ubuntu:~/downloads$ ls -l
. .. units-1.85.tar.gz</cli>

As you can see, the filename ends in ''tar.gz''. The ''tar'' command turns several files and directories into one single //tar// file. This has then been 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.  
<cli>ubuntu@ubuntu:~/downloads$ gunzip units-1.85.tar.gz</cli>

Then extract the contents of the tar file:   
<cli>ubuntu@ubuntu:~/downloads$ tar -xvf units-1.85.tar </cli>

Again, list the contents of the download directory, then go to the **units-1.85** sub-directory.  

<cli>ubuntu@ubuntu:~/downloads$ cd units-1.85
ubuntu@ubuntu:~/downloads/units-1.85$</cli>

<note>You can save a command by using the shortcut:
<cli>tar xvfz units-1.85.tar.gz</cli>
The ''z'' option tells the ''tar'' command to uncompress the tar file before extracting its contents.</note>



===== 7.5 Configuring and creating the Makefile =====

The first thing you should 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.   

<cli>ubuntu@ubuntu:~/downloads$ mkdir ~/units185</cli>

Then run the ''configure'' utility setting the installation path to this. 
<cli>ubuntu@ubuntu:~/downloads/units-1.85$ ./configure --prefix=$HOME/units185</cli>

<note>The ''**$HOME**'' variable is an example of an //environment variable//. The value of ''$HOME'' is the path to your home directory. Just type 
<cli>ubuntu@ubuntu:~/downloads$ echo $HOME </cli>
to show the contents of this variable. We will learn more about //environment variables// in a [[eg-253:unix8#environment_variables|later section]].</note>

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 change its contents. 


===== 7.6 Building the package  =====
 
Now you can go ahead and build the package by running the ''make'' command.  
<cli>ubuntu@ubuntu:~/downloads/units-1.85$ make</cli>

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
<cli>ubuntu@ubuntu:~/downloads/units-1.85$ make check</cli>

If everything is okay, you can now install the package.   
<cli>ubuntu@ubuntu:~/downloads/units-1.85$ make install</cli>

This will install the files into the **~/units185** directory you created earlier.


===== 7.7 Running the software =====

Assuming everything worked, you are now ready to run the software: 
<cli>ubuntu@ubuntu:~/downloads/units-185$ cd ~/units185
ubuntu@ubuntu:~/units185$</cli>

If you list the contents of the **units185** 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 

<cli>ubuntu@ubuntu:~/units185/bin$ ./units</cli>

As an example, convert 6 feet to metres.  

<cli>You have: 6 feet
You want: metres  

* 1.8288 </cli>

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  

<cli>ubuntu@ubuntu:~/units185/info$ info --file=units.info</cli>




===== 7.8 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 unlikely 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 **units185** installation directory.  

<cli>ubuntu@ubuntu:~$ cd ~/units185/bin
ubuntu@ubuntu:~/downloads$ ls -l </cli>

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

<cli>ubuntu@ubuntu:~/units185/bin$ file units

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

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

<cli>ubuntu@ubuntu:~/units185/bin$ strip units
ubuntu@ubuntu:~/units185/bin$ ls -l</cli> 

As you should see, the file should now be around 36 kbytes -- a third of its original size. Two thirds of the binary file was debug code!!!

Check the file information again.  

<cli>ubuntu@ubuntu:~/units185/bin$ file units

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

Sometimes 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''.


----

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 --- //[[C.P.Jobling@Swansea.ac.uk|Dr Chris P. Jobling]] 2007/09/21 18:08//