I have a post-update hook on my server, such that when I

git push

it does a pull on the live web directory. However, while the push always succeeds, the post-update hook sometimes fails.

The hook is pretty simple:

#!/bin/sh
#
# An example hook script to prepare a packed repository for use over
# dumb transports.
#
# To enable this hook, rename this file to "post-update".
cd /var/www
env -i git pull

I'm pushing updates from a variety of places, but sometimes I have to login as root on the server and manuall do a

env -i git pull

I only have to do it 20% of the time though. Any ideas why it would fail randomly? Thanks!