rake background task can not run

Question

I want to use rake background task in rails like this

system("cd #{Rails.root} && RAILS_ENV=#{Rails.env} rake abc:def --trace 2>&1 >> #{Rails.root}/log/rake.log &")

This is ok in development environment, but will not work in production mode.

I used logger to check whether the command string is generated ok or not, but it seems every things is fine in production evironment:

cd /home/username/rails_staging/Abc/releases/20100904034630 && RAILS_ENV=production rake abc:def --trace 2>&1 >> /home/username/rails_staging/Abc/releases/20100904034630/log/rake.log &

Any body has any ideas about why this can not work in production mode?

Thanks