From Mojave in System Preferences / Software Update, I'm trying to update to Catalina.
Catalina takes about 8 GB.
The network cable was a bit loose, and after about 6 GB (75%), someone touched the cable and the download was interrupted with an error message: "Network connection was lost!".
I just clicked "Ok" (no reboot…) and was offered the update again. That I did. But the updater started almost from the beginning! (from 512 MB to be precise!). I was expecting MacOS to use the part that was already downloaded (or at least most of it), in order to spare another 30 minutes download!
Is there a way (update from command line…) to tell MacOS to consider using the part of the file that was already downloaded at the time of the disconnection?
Best Answer
As far as I'm aware this is not possible, the update process gets interrupted and the temporary download gets removed.
This is inefficient, but due to the tool
softwareupdatebeing apple proprietary there is no at home fix for this. To prevent this from happening in the future, you might be able to download the update manually with wget from a server that supports download continuation. (Most webservers these days)But unless you're heavily starved on a data cap, just restarting the download from start saves you from a headache