How to rsync a chroot without breaking symlinks?

Question

I'd like to rsync (backup) a chroot environment from outside the chroot. For that I first make a lvm snapshot of the chroot volume and then run rsync on that.

The only problem with this approach: Symlinks that inside the chroot are absolute are now pointing to the outer-chroot-system and are of course not matching. Since I would like to use copy-unsafe-links, this leads to a false link resolution. Is there a way to make rsync resolve symlinks from another directory than the main root or is there another way to solve this?

Answer 1

You could replace your absolute symlinks with relative ones before doing the rsync.

Answer 2

Changing all absolute symlinks to relative is definitely a good solution, if it can't be done, a convoluted and inefficient way around it that could work is use sshfs that has a --transform_symlinks option to do just that.

You'd need to set a separate ssh server or a user with a separate configuration in the currently running sshd and use a combination of

Subsystem sftp internal-sftp

and

ChrootDirectory /path/to/jail

Now, if you're --copy-unsafe-link and thus don't care to preserve symlinks or save space, you could just run rsync chrooted inside the jail (copy a statically linked rsync there, run nscd, bind-mount /var/run/nscd and exclude both /var/run/nscd and that rsync binary from the sync (you may have to bind-mount /dev and/or proc as well and use --one-file-system))