It's important that you know what is happening here.
sed is, as Bernhard tells you, a stream editor. It runs through a file
making edits.
The -i option allows you to change a file in place.
s/foo/bar will SUBSTITUTE (s) the phrase 'foo' with replacement 'bar'
So that first command in dom0 went through the file
/etc/yum.repos.d/qubes-dom0.repo and on every line where it found:
yum.qubes-os.org
changed it to:
yum.qubesos4rrrrz6n4.onion
and then saved the changed file.
Instead of the sed command, the instructions could say:
1. Open the file /etc/yum.repos.d/qubes-dom0.repo in your favourite text
editor.
2. Look for every occurrence of
yum.qubes-os.org, and change it to
yum.qubesos4rrrrz6n4.onion.
3. Save the changed file.
If you really want to set it back you can either reverse the sed
command, or make the changes manually in a text editor.
That is:
1. Open the file /etc/yum.repos.d/qubes-dom0.repo in your favourite text
editor.
2. Look for every occurrence of yum.qubesos4rrrrz6n4.onion and change it to
yum.qubes-os.org.
3. Save the changed file.
Do the same for the other file.
That's reversed the changes you made.
The two variables that "dont exist" are just placeholders for the name
of the template that you want to change.
So instead of $DebianTemplateVM type in the name of the Debian template
that you want to affect.
The qvm-run command allows you to run programs on qubes from dom0 - in
this case, using sed allows you to change those files quickly from dom0
instead of opening the TemplateVM, firing up a text editor and making
the changes in the TemplateVM.
What's puzzling is that you find that you can't connect to the update
servers anymore. (I assume that you mean from dom0 because you didnt
make any changes in Templates.)
It occurs to me that it doesn't actually say on the page that you will
need your updateVM to be running behind a Tor gateway for this method to
work. Perhaps you knew this? Perhaps not. You should ensure that you
made this change - if your updateVM is NOT running through Tor then
updates will always file. If it IS then they will fail some of the time
- that seems to be inevitable using Tor.
If you really do want to revert then you dont need to worry about this.
Just revert the changes you made in the .repo files and things should
work again.
unman
unman