%general-entities; ]> 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 . 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. Before measuring the build time of any package (no matter Binutils pass 1 or a package of which the SBU is being measured), make sure a system power profile suitable to make the system running with the maximum performance (and the maximum power consumption) is selected. Or the measured SBU value may be severly inaccurate because the system may be operated differently building Binutils pass 1 and the other package. Be aware that a significant inaccuracy can still show up even if the same profile (except one maximizing the performance) is used for both packages: the system may respond slower for saving the power building Binutils pass 1, because the system load seems only about 25% of the load building the other package (with -j4). On most distros the power profile can be managed with either power-profiles-daemon or tuned. If the distro runs power-profiles-daemon, issue the powerprofilesctl set performance command to select the performance profile. If the distro runs tuned, issue the tuned-adm profile throughput-performance command to select the throughput-performance profile. Even if you are not measuring the SBU values, it's still better to select the power profile for maximum performance before building LFS, as doing so can (obviously) make the system faster to build LFS packages. 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.