How to specify in crontab by what user to run script?

EDIT: Note that this method won't work with crontab -e, but only works if you edit /etc/crontab directly. Otherwise, you may get an error like /bin/sh: www-data: command not found

Just before the program name:

*/1 * * * * www-data php5 /var/www/web/includes/crontab/queue_process.php >> /var/www/web/includes/crontab/queue.log 2>&1

Since you're running Ubuntu, your system crontab is located at /etc/crontab.

As the root user (or using sudo), you can simply edit this file and specify the user that should run this command. Here is the format of entries in the system crontab and how you should enter your command:

# m h dom mon dow user  command
*/1 * * * * www-data php5 /var/www/web/includes/crontab/queue_process.php >> /var/www/web/includes/crontab/queue.log 2>&1

Of course the permissions for your php script and your log file should be set so that the www-data user has access to them.

Instead of creating a crontab to run as the root user, create a crontab for the user that you want to run the script. In your case, crontab -u www-data -e will edit the crontab for the www-data user. Just put your full command in there and remove it from the root user's crontab.

Mike's suggestion sounds like the "right way". I came across this thread wanting to specify the user to run vncserver under on reboot and wanted to keep all my cron jobs in one place.

I was getting the following error for the VNC cron:

vncserver: The USER environment variable is not set. E.g.:

In my case, I was able to use sudo to specify who to run the task as.

@reboot sudo -u [someone] vncserver ...