Why this crontab does not work?

[Magicloud Magiclouds <magicloud.magiclouds@gmail.com>]

Dear all,
   I have a crontab like this:

root@localhost # crontab -l
# m h  dom mon dow   command
*       0,12    *       *       *       root    /root/update.sh
root@localhost # more /root/update.sh
#!/bin/bash
apt-get update
apt-get upgrade -d
apt-get autoclean
apt-get autoremove
touch /root/update.sh
root@localhost # ls -l /root/update.sh
-rwxr-xr-x 1 root root 104 2007-07-19 09:01 /root/update.sh


   But it seems that the script have never been called.

Thanks.