Ssh – RSync over SSH – permission denied even though the user is in the root group

permissionsrootrsyncssh

I have a need to copy files between servers through the web. I'm using RSYNC over ssh to do so.
The problem is, I need to be able to transfer files, no matter where the files is.

I created a user rsync and : usermod -G root -a rsync to give him the right to read/write anywhere on both servers.

During the transfer, I see this error: 

rsync: mkstemp "/root/.myFile.RDr2HY" failed: Permission denied (13)

I don't understand what's happening.

edit: I just found out that the destination folder didn't have the write access for the root group. How would I give 100% access to this rsync user ? If I change its uid to 0, rsync stop working.

Best Answer

What you've done, usermod -G root -a rsync, is to add the rsync user to the root group. This has no effect whatsoever on most systems, because the root group is not special. There are systems where being in the root group is necessary to escalate privileges to the root user, but it is never sufficient (the root group is the group of users who may use sudo, or some equivalent setup).

In terms of security, giving a user the permission to write files anywhere is exactly equivalent to giving that user root powers. (The user can overwrite /bin/su, or /etc/passwd, or /usr/sbin/sshd, or any number of other programs and databases that would let her set up a backdoor for herself.)

If you need to access arbitrary files over ssh, allow ssh logins as root. Not with a password (or else a long, randomly generated one), just with a key (which you'll need to protect carefully, of course). In /etc/sshd_config, put

PermitRootLogin yes
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