Thanks. Indeed, I am using Mint.
Running the sudo command did not install the packages, according to the output of afni_system_check.py (I see a warning that afex, phia and brms are not installed).
Running the grep command, I get the following output:
/etc/apt/sources.list:deb [
cran.cnr.berkeley.edu] rebecca/
/etc/apt/sources.list:deb [
cran.cnr.berkeley.edu] rebecca/
/etc/apt/sources.list:deb [
cran.cnr.berkeley.edu] rebecca/
/etc/apt/sources.list:deb [
cran.cnr.berkeley.edu] rebecca/
/etc/apt/sources.list:deb [
cran.cnr.berkeley.edu] rebecca/
/etc/apt/sources.list:deb [
cran.cnr.berkeley.edu] rebecca/
