I'm running this simple script on my Raspberry Pi to auto update so I can forget about it. It also keeps a log that says whether the update was successful. The script is update.sh:

#!/bin/bash echo "Update starts on: $(date)" >> /home/pi/update.log  if apt-get update && apt-get upgrade -y; then     echo "update successful $(date)"  >> /home/pi/update.log  else     echo "Couldn't update $(date)" >> /home/pi/update.log  fi

I added this script to the root crontab by using sudo crontab -e and the cronjob is set to run every day at 6AM

0 6 * * * /home/pi/update.sh

I know that it works to some extent because running sudo ./update.sh in the shell manually runs the commands and leaves a "successful" entry in the log. On the other hand, when ran from the crontab, I always get the "couldn't update" entry. In case it matters, the "update.sh" script was created by the "pi" user and I never changed the permissions, except giving it execution permissions.

I read another question about the same problem and the guy solved it by putting a sudo in front of the command. He admits it's weird because it's already being executed by root, but says it works. I tried adding the sudo and verified it actually works now.

Does anyone know why this happens? Why does it need the sudo if it's already root?

linux bash shell cron raspberry-pi

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This is because the cron is running as your unprivileged user, and the apt-get commands require root (aka administration) elevation privileges to run.

An alternative is to run this command under the root user's crontab:

sudo -i <type user password> crontab -e

The first command elevates your entire shell to root and will also - crucially - give you access to root's environment, rather than just a single command as your user with elevated privileges.

The second command will edit the root crontab, not your own.

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