GFortran error: ld: library not found for -lSystem when trying to compile

Solution 1:

On macOS Big Sur v11.1:

Relevant SO post: https://apple.stackexchange.com/questions/408999/gfortran-compiler-error-on-mac-os-big-sur

The fix is to add the stdlib to your $LIBRARY_PATH. For some reason or another it isn't in your standard $PATH anymore on 11.1.

export LIBRARY_PATH="$LIBRARY_PATH:/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/lib"

(or add it to login file and restart terminal).

Solution 2:

I'll also chime in (19 Dec 2020) that I just updated from MacOS Mojave to Catalina and suddenly got this error.

It resolved itself with

brew reinstall gcc
brew reinstall gfortran

Solution 3:

Update: I tried what was suggested and installed the gfortran build from the gcc package using homebrew which gave me a newer version of gfortran and my problem was fixed!

Solution 4:

For those using MacPorts.

# Installed `gcc8` and `gcc_select`
sudo port install gcc_select gcc8

# then to create "gfortran" softlink to "gfortran-mp-8"
sudo port select --set gcc gcc8

# and added to my .profile
export LIBRARY_PATH="$LIBRARY_PATH:/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/lib"

I did ls -l /Library/Developer/CommandLineTools/SDKs/ and found that Xcode had installed one SDK for Catalina and one for Big Sur. I changed the soft link for MacOSX.sdk to point to the Catalina version.