Check automatically for update in Debian

The package cron-apt is designed to automatically update the package list and download upgraded packages. Therefore it basically calls the command [1]:

apt-get update

To install cron-apt:

sudo apt-get install cron-apt

By default, cron-apt uses cron to run regularly (each day at 4am). This method is not convenient for a personal desktop computer which is often turned off at that time.

You can use anacron instead of cron to execute cron-apt regularly. For doing this, just link the executable in the /etc/cron.daily/ directory:

sudo ln -s /usr/sbin/cron-apt /etc/cron.daily/

However anacron is automatically launched each day at 7:30 am by cron. The command that launch anacron by cron is found in this file: /etc/cron.d/anacron. Once again, this could be not optimal for a desktop computer. Furthermore when you start your laptop without power supply anacron won’t be launched. You can then add another, more convenient, entry in the /etc/cron.d/anacron file to launch anacron at 12:30 pm for example. The full /etc/cron.d/anacron file then looks like:

# /etc/cron.d/anacron: crontab entries for the anacron package

SHELL=/bin/sh
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin

30 7    * * *   root    test -x /etc/init.d/anacron && /usr/sbin/invoke-rc.d anacron start >/dev/null
30 12    * * *   root   test -x /etc/init.d/anacron && /usr/sbin/invoke-rc.d anacron start >/dev/null

I always use the command line, then it can be very convenient to display a message with the number of updates available for my system when I log in to my favourite shell. To do so I added this line to the anacrontab (/etc/anacrontab):

1   10  check_update echo "$(date +'%Y%m%d %T') $(aptitude search '~U' | wc -l) packages can be updated." > /home/USER/.motd # message of the day

And I use the following script to print the message of the day when I start a new shell:

Then I added the following command to my shell configuration script (.bashrc, .zshrc, …):

~/PATH/TO/THE/SCRIPT/print_motd.sh # Message of the day