Safe rsync with no passwords between two systems

rootrsync

We are trying to implement a safe rsync for backups between 2 servers. We are trying by all means to avoid having root access with no passwords between the 2 systems and if any just do that for an specific user.

I understand this has issues with permissions of the backed up files. I've read here in serverfault and also on this site about using fakeroot and about the "PermitRootLogin forced-commands-only" option of SSH server but still can't figure out what is the most logical and reasonable option from a security point of view. We do not want a root user to automatically have root access on the other machine without a password. Not sure if we are just to paranoid about it but as I suppose this is something pretty usual any feedback would be mostly appreciated.

  • Does the PermitRootLogin forced-commands-only with a pair of keys for no password be good enough? Does this need an specific list of allowed commands on the destination server (i.e rsync)?
  • Would the fakeroot option work (mainly data backups in our case) and if so… how is it combined with the rsync command?
  • Can we have an rsync user with
    sufficient permissions on both
    systems so the passwordless rsync
    works fine?

Many thanks.

Best Answer

You are right that passwordless root login on either your live machine(s) or your backup machine(s) is a bad idea - if someone gains access to one side they immediately have access to the other so can damage both your live data and online backups at the same time.

The fakeroot option should work fine if your to-be-backed-up servers are pushing updates to those storing the backups and you just need to add --fake-super to the rsync command line and make sure that the filesystem at the receiving end supports extended attributes.

Another option is to introduce an intermediate machine that both the live and backup servers have key-base root logins to. That was the live machines can push backups to the intermediate machine with rsync and afterwards the backup machines can pull them down, without either live or backup machines being able to login to each other at all, never mind as root. The intermediate machine doesn't need to be able to authenticate with either live or backup servers either. The intermediate server only needs enough space to hold the ltest versions of everything (i.e. the data stored on the backup servers including snapshots from different times could be several times larger than the intermediate server can store.

Of course it goes without saying that as well as disallowing key-based root login between servers you make sure that the root (and other) passwords all differ from machine to machine too.

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