I mistakenly added two lines with 'testing' to my 'sources.list' file,
which now looks like this:
deb http://debian.osuosl.org/debian/ stretch main non-free contrib
deb-src http://debian.osuosl.org/debian/ stretch main non-free contrib
deb http://security.debian.org/debian-security stretch/updates main
contrib non-free
deb-src http://security.debian.org/debian-security stretch/updates
main contrib non-free
deb http://debian.osuosl.org/debian/ stretch-updates main contrib
non-free
deb-src http://debian.osuosl.org/debian/ stretch-updates main
contrib non-free
# my bad:
deb http://ftp.us.debian.org/debian/ testing main non-free contrib
deb-src http://ftp.us.debian.org/debian/ testing main non-free contrib
I have read that it's difficult or impossible to revert to 'stable' once
'testing' packages have been installed. I have also read that it's not a
good idea to have both 'stable' and 'testing' repositories in
'sources.list', so I'm wondering how to proceed. I experimented with
replacing 'stretch' by 'buster' in the first six lines above (and
removing the last two lines), but then the system couldn't find the
stable google-chrome repository in '/etc/apt/sources.list.d'. I now
have the uncomfortable feeling that I'm playing with fire.
Thanks in advance for any suggestions about if/how I should edit my
'sources.list' file!
-Paul