Category: Linux

How to set C, C++ or Fortran compiler for CMake

To use a different compiler (e.g. Intel Compiler, CLANG or PGI) or a different version then CMake uses by default, one can either set environment variables or modify
the CMakeLists.txt file.

CMake evaluates the environment variables CC for the C compiler, CXX for the C++ compiler and FC
for the Fortran compiler:

CC=/path/to/icc cmake ..
CXX=/path/to/icpc cmake ..
FC=/path/to/ifort cmake ..

For a more permanent solution, one can also edit the CMakeLists.txt file:

SET(CMAKE_C_COMPILER /path/to/pgcc)
SET(CMAKE_CXX_COMPILER /path/to/pgc++)
SET(CMAKE_FC_COMPILER /path/to/pgfortran)

BTW: The environment variables LDFLAGS, CFLAGS, CXXFLAGS or FFLAGS are also evaluated by CMake.

SPACK and Intel Parallel Studio: “error while loading shared libraries:”

Spack is a package manager for supercomputers, Linux, and macOS. It makes installing scientific software easy. With Spack, you can build a package with multiple versions, configurations, platforms, and compilers, and all of these builds can coexist on the same machine.

However, when using the Intel Compiler as compiler, I got the following error for some packages:

 error while loading shared libraries: cannot open shared object file: No such file or directory

To solve this, edit your ~/.spack/linux/compilers.yaml file and set the extra_rpaths to your Intel Compiler libraries directory:

- compiler:
    environment: {}
    extra_rpaths: [/opt/intel/compilers_and_libraries_2018.1.163/linux/compiler/lib/intel64/]
    flags: {}
    modules: []
    operating_system: centos7
      cc: /opt/intel/compilers_and_libraries_2018.1.163/linux/bin/intel64/icc
      cxx: /opt/intel/compilers_and_libraries_2018.1.163/linux/bin/intel64/icpc
      f77: /opt/intel/compilers_and_libraries_2018.1.163/linux/bin/intel64/ifort
      fc: /opt/intel/compilers_and_libraries_2018.1.163/linux/bin/intel64/ifort
    spec: intel@18.0.1
    target: x86_64

BASH: Nach jedem xten Zeichen ein Zeichen in einen String einfügen

Mit sed "s/.\{x\}/& /g" kann man in eine Zeichenkette alle x Zeichen ein Leerzeichen automatisiert einfügen. Aber auch andere Zeichen sind möglich. So kann man bspw. alle zwei Zeichen einen Doppelpunkt in einen String einfügen:

#~> echo "AA11CC22EE" | sed "s/.\{2\}/&:/g"

Sollte das letzte Zeichen stören, kann man dies wie folgt entfernen:
#~> a = $(echo "AA11CC22EE" | sed "s/.\{2\}/&:/g")
#~> echo ${a%?}


When cmake complains about a missing MHD library, install the microhttpd library development files.


 yum install libmicrohttpd-devel

Or download the up-to-date release from and compile and install it with:

tar -xzf libmicrohttpd-latest.tar.gz
cd libmicrohttpd-*
./configure && make install

NVIDIA CUDA on Ubuntu: unsupported GNU version! gcc versions later than 5 are not supported!

After installing CUDA on Ubuntu, compiling CUDA applications with nvcc results in an error similar to this:

In file included from /usr/local/cuda-8.0/bin/../targets/x86_64-linux/include/cuda_runtime.h:78:0,
from <command-line>:0:
/usr/local/cuda-8.0/bin/../targets/x86_64-linux/include/host_config.h:119:2: error: #error — unsupported GNU version! gcc versions later than 5 are not supported!
#error — unsupported GNU version! gcc versions later than 5 are not supported!

Ubuntu comes with a more up-to-date GCC then CUDA can handle. To solve this issue we install GCC 4.9:

sudo apt install gcc-4.9 g++-4.9

Now GCC 4.9 and the up-to-date GCC are installed on the system. To be able to use the up-to-date GCC without CUDA, one can setup and use the “update-alternatives” system for GCC. In this case we replace the default GCC 6 compiler:

sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-6 60 --slave /usr/bin/g++ g++ /usr/bin/g++-6
sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-4.9 50 --slave /usr/bin/g++ g++ /usr/bin/g++-4.9

Now we can list the available compilers with

update-alternatives --list gcc

and set the GCC 4.9 as default with

update-alternatives --set gcc /usr/bin/gcc-4.9