They should stick the changes, it’s not a temporary change as you are editing and saving the actual file via virtualmin.
I just changed my upload from 2mb to 10mb as a test in the vhosts php config area and just did a reboot as a test and changes still apply.
You can see a screenshot of it here.
As you see I edited the php config for that specific vhost and and clicked save then rebooted the entire server as a extreme test based on your reply, and the changes still applied, I didn’t just change them before the pic was taken to fool you.
If the changes aren’t saving and not continuing to be applied after a reboot, then you probably have a more serious file permission issue between virtualmin and directories, users etc. But thats out of my knowledge unfortunately and a recent fresh install I did, does save over reboots as you can see.
Are you making sure you log in as root/sudo user when trying to save etc which is what I was when I saved the changes?
Ahhh I see your original answer you want them as defaults.
My screenshot above will show you for current servers.
For global one way if its there is a better way I’m not sure would be to change them in the Webmin (tab) / Others / PHP Configuration / Manage button / then Resource Limits.
But I don’t know if there’s a better way to do this so make sure you take note of what you change just incase you need to revert.
From virtualmin, that way seems to be the best globally I think for new servers.
Template PHP configuration file
By default, when a virtual server runs PHP scripts as the server’s owner, Virtualmin will copy the system’s global PHP configuration file (usually /etc/php.ini) to the domain’s ~/etc directory. This allows PHP options to be set differently on a per-server basis.
Screenshot to help you.
Then you will see a screen to above and click Resources button in the middle with the 2 blue bars.
That will do it on a global scale for all new servers current ones you will need to edit as my first screenshot.
And Yes changes do stick over reboot.
Be warned if you are changing them there set low initially for a reason and yes you need to change them occasionally for things, last thing you are wanting to do is globally allow every host uploading 40mb files to your server. So have a good think why you want to make the change and if its needed on every site or not.