Notes on Building Software

The golden rule of Unix System Administration is to use your superpowers only when necessary. Hence, BLFS recommends that you build software as an unprivileged user and only become the root user when installing the software. This philosophy is followed in all the packages in this book. Unless otherwise specified, all instructions should be executed as an unprivileged user. The book will advise you on instructions that need root privileges.

If a file is in .tar format and compressed, it is unpacked by running one of the following commands:

tar -xvf filename.tar.gz
tar -xvf filename.tgz
tar -xvf filename.tar.Z
tar -xvf filename.tar.bz2

You can also use a slightly different method:

bzcat filename.tar.bz2 | tar -xv

Finally, you sometimes need to be able to unpack patches which are generally not in .tar format. The best way to do this is to copy the patch file to /usr/src and then run one of the following commands depending on whether the file is a .gz or .bz2 file:

gunzip -v patchname.gz
bunzip2 -v patchname.bz2

Generally, to verify that the downloaded file is genuine and complete, many package maintainers also distribute md5sums of the files. To verify the md5sum of the downloaded files, download both the file and the corresponding md5sum file to the same directory (preferably from different on-line locations), and (assuming file.md5sum is the md5sum file downloaded) run the following command:

md5sum -c file.md5sum

If there are any errors, they will be reported. Note that the BLFS book includes md5sums for all the source files also. To use the BLFS supplied md5sums, you can create a file.md5sum (place the md5sum data and the exact name of the downloaded file on the same line of a file, separated by white space) and run the command shown above. Alternately, simply run the command shown below and compare the output to the md5sum data shown in the BLFS book.

md5sum [name_of_downloaded_file]

For larger packages, it is convenient to create log files instead of staring at the screen hoping to catch a particular error or warning. Log files are also useful for debugging and keeping records. The following command allows you to create an installation log. Replace [command] with the command you intend to execute.

( [command] 2>&1 | tee compile.log && exit $PIPESTATUS )

2>&1 redirects error messages to the same location as standard output. The tee command allows viewing of the output while logging the results to a file. The parentheses around the command run the entire command in a subshell and finally the exit $PIPESTATUS command ensures the result of the [command] is returned as the result and not the result of the tee command.