4.5. About SBUs

Many people would like to know beforehand approximately how long it takes to compile and install each package. Because Linux From Scratch can be built on many different systems, it is impossible to provide absolute time estimates. The biggest package (gcc) will take approximately 5 minutes on the fastest systems, but could take days on slower systems! Instead of providing actual times, the Standard Build Unit (SBU) measure will be used instead.

The SBU measure works as follows. The first package to be compiled is binutils in Chapter 5. The time it takes to compile using one core is what we will refer to as the Standard Build Unit or SBU. All other compile times will be expressed in terms of this unit of time.

For example, consider a package whose compilation time is 4.5 SBUs. This means that if your system took 10 minutes to compile and install the first pass of binutils, it will take approximately 45 minutes to build the example package. Fortunately, most build times are shorter than one SBU.

SBUs are not entirely accurate because they depend on many factors, including the host system's version of GCC. They are provided here to give an estimate of how long it might take to install a package, but the numbers can vary by as much as dozens of minutes in some cases.

Note

For many modern systems with multiple processors (or cores) the compilation time for a package can be reduced by performing a "parallel make" by either setting an environment variable or telling the make program how many processors are available. For instance, an Intel i5-6500 CPU can support four simultaneous processes with:

export MAKEFLAGS='-j4'

or by building with:

make -j4

When multiple processors are used in this way, the SBU units in the book will vary even more than they normally would. In some cases, the make step will simply fail. Analyzing the output of the build process will also be more difficult because the lines from different processes will be interleaved. If you run into a problem with a build step, revert to a single processor build to properly analyze the error messages.

The times presented here are based upon using four cores (-j4). The times in Chapter 8 also include the time to run the regression tests for the package unless specified otherwise.