time machine backup

[oceangirl10]

I rarely do time machine backups, but want to try doing one. I have an external HD plugged in that has plenty of space on it. I click the clock icon at the top of the screen and press "back up now" and get the message "Backup disk not available. Try backing up again when "Mac OSX Install ESD" is available." What does this mean and how do I do a time machine backup?

 

[maflynn]

You need to tell macOS to use the drive for Time Machine first. Go into System Preferences, then click on Time Machine. Then select Backup Disk

 

[kohlson]

I like TM, and it's been helpful. One thing that was not intuitive to me was how to exclude certain directories. After selecting the disk in TM Preferences, you *add* directories to the list to be excluded using the plus sign.