Back up other drive using Time Machine I'm trying to diagnose &amp; fix some problem on my MacBook Pro - the machine randomly hard-crashes instantly &amp; shuts down.

I have a somewhat-old Time Machine backup of the drive on an external USB disk, and I would like to update that backup.  The problem is that it keeps crashing in the middle of backups, then forcing a complete disk scan, which takes a really long time, so it never gets to complete a new snapshot.

To try to make progress, I created an external bootable drive, which I can use to get the laptop started.  I can also mount my Time Machine backup drive - both are external USB drives.  I was hoping to tell Time Machine to resume backing up the laptop's internal drive to the Time Machine drive, but I don't see any obvious way to do that.

Is there some way I'm missing?  Maybe using tmutil from the command line?
Time Machine is optimized to create and maintain a history of file-level backups of all files/folders on your system. What you rather need is a disk/image level backup which just dumps the whole drive onto an external drive. You can afterwards either copy the whole image back again or, probably more useful, get specific folders back.

The two applications people tend to use for this are CCC and SuperDuper!. You also need an additional external USB drive at least as big as your internal drive.