test/improve pull backup docs

[ThomasWaldmann]

The pull backup docs (see deployment / ...) have 2 rather severe warnings and one warning that --numeric-ownermight be better.

This should be tried / improved / cleaned up via a PR by someone who actually uses pull backups (I don't).

https://github.com/borgbackup/borg/blob/949ca476527422909c8e89ed087cd6a9ce0a957b/docs/deployment/pull-backup.rst

[ThomasWaldmann]

@Thalian @Gu1nness @remyabel can you please have a look?

[fantasya-pbem]

What is wrong with these warnings? In pull backup there are a lot of things to consider, so I think that all aspects and possibilities should be discussed in detail. We could remove the Warning signs...

[fantasya-pbem]

Something we could fix: "ssh-agent" is displayed as an own deployment article in the menu on the left, but it is on the same page as the pull mode article - either move it to its own page or change the header to a subtitle of pull mode.
This has been fixed in master already, so I will backport this to 1.1-maint.

[ThomasWaldmann]

Well, if you give the backup server access to the backup clients's root fs, it is somehow expected that this is dangerous to the client as the backup server then can basically harm the client.

A bit less expected is that the chroot method also could do harm in the other direction because it will execute code from the client. Also, the problem why chroot was used isn't really solved by chroot.

[fantasya-pbem]

Also, the problem why chroot was used isn't really solved by chroot.

It was solved when I did test this setup after writing the docs.

I'll have a look into it and see if something can be improved in terms of security.

[ThomasWaldmann]

"was solved" -> only for simple scenario, see that 3rd(?) warning in the docs about the scenario when that does not work.

[fantasya-pbem]

Sure, there are scenarios when this doesn't work. So this issue is not about "testing if this scenario works and fix bugs", but about "adapt this method for other scenarios".

[fantasya-pbem]

I'll restructure this page and add more receipts for other scenarios. Add me as assignee if you like to.