I intend to put my computer to sleep every night and make it wake up again next morning. I found that rtcwake would serve my purpose. However putting it in the crontab does nothing. Following is my crontab entry for "root" user

0 1 * * * rtcwake -m disk -s 25200

I added it using 'sudo crontab -e'. The syslog shows that it executed the command, but the computer does not sleep. If I run the command on terminal directly, the computer is put to sleep immediately as expected. So I don't think there is any problem with ACPI.

Does anyone have a clue? I am on Ubuntu 14.04