# Linux

• GCC version 4.7 or later is required to build Julia.
• To use external shared libraries not in the system library search path, set USE_SYSTEM_XXX=1 and LDFLAGS=-Wl,-rpath,/path/to/dir/contains/libXXX.so in Make.user.
• Instead of setting LDFLAGS, putting the library directory into the environment variable LD_LIBRARY_PATH (at both compile and run time) also works.
• The USE_SYSTEM_* flags should be used with caution. These are meant only for troubleshooting, porting, and packaging, where package maintainers work closely with the Julia developers to make sure that Julia is built correctly. Production use cases should use the officially provided binaries. Issues arising from the use of these flags will generally not be accepted.

## Architecture Customization

Julia can be built for a non-generic architecture by configuring the ARCH Makefile variable in a Make.user file. See the appropriate section of Make.inc for additional customization options, such as MARCH and JULIA_CPU_TARGET.

For example, to build for Pentium 4, set MARCH=pentium4 and install the necessary system libraries for linking. On Ubuntu, these may include lib32gfortran-6-dev, lib32gcc1, and lib32stdc++6, among others.

You can also set MARCH=native in Make.user for a maximum-performance build customized for the current machine CPU.

## Linux Build Troubleshooting

ProblemPossible Solution
OpenBLAS build failureSet one of the following build options in Make.user and build again: <ul><li> OPENBLAS_TARGET_ARCH=BARCELONA (AMD CPUs) or OPENBLAS_TARGET_ARCH=NEHALEM (Intel CPUs)<ul>Set OPENBLAS_DYNAMIC_ARCH = 0 to disable compiling multiple architectures in a single binary.</ul></li><li> OPENBLAS_NO_AVX2 = 1 disables AVX2 instructions, allowing OpenBLAS to compile with OPENBLAS_DYNAMIC_ARCH = 1 using old versions of binutils </li><li> USE_SYSTEM_BLAS=1 uses the system provided libblas <ul><li>Set LIBBLAS=-lopenblas and LIBBLASNAME=libopenblas to force the use of the system provided OpenBLAS when multiple BLAS versions are installed. </li></ul></li></ul><p> If you get an error that looks like ../kernel/x86_64/dgemm_kernel_4x4_haswell.S:1709: Error: no such instruction: vpermpd \$ 0xb1,%ymm0,%ymm0', then you need to set OPENBLAS_DYNAMIC_ARCH = 0 or OPENBLAS_NO_AVX2 = 1, or you need a newer version of binutils (2.18 or newer). (Issue #7653)</p><p> If the linker cannot find gfortran and you get an error like julia /usr/bin/x86_64-linux-gnu-ld: cannot find -lgfortran, check the path with gfortran -print-file-name=libgfortran.so and use the output to export something similar to this: export LDFLAGS=-L/usr/lib/gcc/x86_64-linux-gnu/8/`. See Issue #6150.</p>
Illegal Instruction errorCheck if your CPU supports AVX while your OS does not (e.g. through virtualization, as described in this issue).