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I want to rsync my server to back up its content. I want to preserve owner/group so that I can later restore the server using the backup. However the server has a different set of users and groups than my local machine, so it doesn't make sense to use native users. I also don't want to run rsync as a root because of security implications. How can I do it?

migrated from serverfault.com Sep 18 '16 at 11:56

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  • --fake-super --numeric-ids seem promising, but need testing. – Michael Sep 14 '16 at 10:58
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    --numeric-ids does need root permissions on the receiver site – rudimeier Sep 14 '16 at 14:58
  • What are your security troubles? – Nils Sep 14 '16 at 15:38
  • If your server is able to automatically login as root on backuphost to "push" backups then it would feel a bit dangerous that an intruder on server could destroy both the server plus backuphost. – rudimeier Sep 14 '16 at 15:50
  • This is (one of) the reason(s) why a pure rsync solution is not a professional backup solution. I'm voting to move your question to Unix/Linux instead; if anyone knows of a way to fix this, they're likely to hang out over there. – Jenny D Sep 14 '16 at 15:55
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You could write a script which saves permissions, user, group per file, maybe just like

getfacl -R / > /tmp/permissions.txt

to be restored if needed by

setfacl --restore=permissions.txt

Then rsync everything including permissions.txt to a normal user account on the backup host.

The downside is that permissions.txt may not be 100% synchron to the actual backup.

Note saving secret files with wrong permissions under a normal user account might be also a security issue! At least the directory containing the whole backup should be readable only by the backup user.

One more security note: permissions.txt on the original host should be also protected, readable only by root.

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I can't offer a solution that doesn't run as root but I can offer the following:

First, if you use --numeric-ids it will preserve the UID/GIDs. If you do a restore with rsync or tar (or anything that doesn't mess with UID/GIDs) you'll be fine.

rsync -avP --numeric-ids

However not running as root is going to be a problem because Unix requires root to create files as another user. You might be able to use selinux to give the command permissions to write any file, but that is rather complex (though --fake-super will help)

Would it meet your security requirements if the backup server used root and the other side didn't?

# run this on the backup host:
rsync -avP --numeric-ids user@SOURCEHOST:/path/to/files/. /path/to/dest/.

As long as root@BACKUPHOST can ssh to user@SOURCEHOST, you'll be fine. Well, mostly fine. If user can't access a file, it won't get backuped. Depending on your situation, that may not be an issue.

  • BTW you may also restrict the "pull backup key" in authorized_keys to one particular rsync command only or more generic to read-only rsync (google: rrsync) – rudimeier Sep 15 '16 at 7:24

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