How to simulate the environment cron executes a script with?

Solution 1:

Add this to your crontab (temporarily):

* * * * * env > ~/cronenv

After it runs, do this:

env - `cat ~/cronenv` /bin/sh

This assumes that your cron runs /bin/sh, which is the default regardless of the user's default shell.

Footnote: if env contains more advanced config, eg PS1=$(__git_ps1 " (%s)")$, it will error cryptically env: ": No such file or directory.

Cron provides only this environment by default :

If you need more you can source a script where you define your environment before the scheduling table in the crontab.

Couple of approaches:

Export cron env and source it:

Add
```
* * * * * env > ~/cronenv
```
to your crontab, let it run once, turn it back off, then run
```
env - `cat ~/cronenv` /bin/sh
```
And you are now inside a sh session which has cron's environment
Bring your environment to cron

You could skip above exercise and just do a . ~/.profile in front of your cron job, e.g.
```
* * * * * . ~/.profile; your_command
```
Use screen

Above two solutions still fail in that they provide an environment connected to a running X session, with access to dbus etc. For example, on Ubuntu, nmcli (Network Manager) will work in above two approaches, but still fail in cron.
```
* * * * * /usr/bin/screen -dm
```
Add above line to cron, let it run once, turn it back off. Connect to your screen session (screen -r). If you are checking the screen session has been created (with ps) be aware that they are sometimes in capitals (e.g. ps | grep SCREEN)

Now even nmcli and similar will fail.