Hi, Christine-

OK, it looks like the symbolic link exists. Just to verify it, what is the output of:

ls -l /usr/lib/x86_64-linux-gnu/libgsl.so.23

?

Since the GSL link exists, I wonder if the problem is with the GSL installation itself. I also find it odd that you would have to install libglu1 separately, because the main installation command has "libglu1-mesa-dev" as part of its installation, and I would just assume that plain ol' libglu1 would be a dependency of that... Just to rule out something like that, could you please run these three commands again via copy+paste into the terminal:

sudo add-apt-repository universe

sudo apt-get update

(This is the main installation command *without* the R part, because you have been working on that separately):

sudo apt-get install -y tcsh xfonts-base libssl-dev       \
                        python-is-python3                 \
                        python3-matplotlib                \
                        gsl-bin netpbm gnome-tweak-tool   \
                        libjpeg62 xvfb xterm vim curl     \
                        gedit evince eog                  \
                        libglu1-mesa-dev libglw1-mesa     \
                        libxm4 build-essential            \
                        libcurl4-openssl-dev libxml2-dev  \
                        libgfortran-8-dev libgomp1        \
                        gnome-terminal nautilus           \
                        gnome-icon-theme-symbolic         \
                        firefox xfonts-100dpi

If you run afni_system_check.py after that, are there still errors?

--pt