Weekly cron job to save list of installed packages

Question

I am having trouble figuring out how to set up my first cron job. I simply want to run this command once every week:

dpkg -l > ~/Dropbox/installed_packages

My /etc/crontab file contains the line

7 6    * * 7   root    test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.weekly )

So I need to place my command somewhere in the directory /etc/cron.weekly - but in which file? /etc/cron.weekly currently contains the following files:

apt-xapian-index  man-db  0anacron  cvs

Answer 1

Create a file with the following content (e.g. list_packages.sh):

#!/bin/bash

dpkg -l > ~/Dropbox/installed_packages

Place this file in /etc/cron.weekly/ and it will run once a week.

Answer 2

Save this as a script, say installed_packages_list.sh:

#!/bin/bash
dpkg -l > ~/Dropbox/installed_packages

Make it executable.

chmod u+x installed_packages_list.sh

Then run

crontab -e

This will open up a file in a text editor. Type this and save

@weekly /full/path/to/script

The script will be executed once a week, with privileges of the user who scheduled the cron job.

Answer 3

First, for doing this you do not need to execute the job as super user.

The easiest way to solve this is to edit the crontab of your normal user via

crontab -e

Depending on you EDITOR enviroment variable, the users crontab is opened with your favourite text editor.

There you can add something like

# m h dom mon dow command
5 12 * * 1 bash $HOME/pkg.backup.sh

You have then to create the pkg.backup.sh file with your dpkg command in it.

Btw, if you want to be able to easily restore your current package state of the machine (aka package selection), then this command line is more target-oriented:

dpkg --get-selections > foo

To restore it, you just have to type

dpkg --set-seclections < foo

Actually, dpkg -l is useful in addition to that if you want to log exact package version number, too.