I\'ve set up gitosis using the tutorial privided at:
http://scie.nti.st/2007/11/14/hosting-git-repositories-the-easy-and-secure-way
I found that I was unable
I know this is short but you probably just need to make the post hook executable...
sudo chmod 755 [your-path-to-your-repo]/gitosis-admin/hooks/post-update