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Running rsync from a webserver (using sudo)

Wed, Oct 21, 2009 mdda OSS Blog Comments

Running rsync from a webserver (using sudo)

Situation

I want to have ‘rsync’ run when a user presses a button on the webserver. The software stack is as follows (though this was largely a red-herring, see below) :

  • Fedora - server

  • lighttpd - webserver

  • Twiki - intranet setup

  • perl - plugin language for Twiki

  • bash - perl launches a script to run the rsync

  • sudo - to ‘change user’ to the one with the correct permissions for the source folder

  • rsync - the actual backup utility

  • ssh - file transfer mechanism, and auto-login (via its private key) to the remote server

Solution

It turns out that it wasn’t perl ‘Taint’ that was stopping the rsync from running… Nor lighttpd, nor the ‘user’ for the ‘ssh’ embedded in the rsync command…

To cut a long story short, the final solution revolved around understanding the additional ‘requiretty’ constraints that Fedora (and maybe other distributions) has for sudo.

The perl command to run

push @res, map { "\n   * $_" } split("\n", `/home/webserver/.../rsync_R_drive.bash 2>&1`);

The bash script to run

#! /bin/bash

sudo -u admin \
  /usr/bin/rsync -av \
  -e "/usr/bin/ssh -i /home/admin/.ssh/id_dsa" \
  /home/somewhere/only/admin/can/access/* \
  remoteuser@remotemachine.com:~/target-directory/

Set up for the ‘sudoers’ file

Edit ‘sudoers’ file using this command :

EDITOR=joe; visudo

and add (to the /etc/sudoers file):

Defaults:lighttpd   !requiretty
lighttpd        ALL=(admin) NOPASSWD: /usr/bin/rsync

And enable password-less login by ‘admin’ on the remote server

On the local machine :

local$ ssh-keygen -t rsa
local$ ssh-copy-id remoteuser@remotemachine.com


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