I am trying to do a full Time Machine Backup to a new external disk. The backup starts, and it says "Time remaining about 4 days." That seems like a very long time, but the real problem is that the computer "logs off" after a few hours, and the b.u. stops

Question

I am trying to do a full Time Machine Backup to a new external disk. The backup starts, and it says "Time remaining about 4 days." That seems like a very long time, but the real problem is that the computer "logs off" after a few hours, and the backup stops. The system preferences are set to "Never" for Computer sleep and Display sleep. The computer does not ordinarily log off automatically, but it has done this twice since I started the Time Machine backup.

Answer 1

If you have more than one user account, these instructions must be carried out as an administrator.
Launch the Console application in any of the following ways:
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.
☞ Open LaunchPad. Click Utilities, then Console in the icon grid.
Make sure the title of the Console window is All Messages. If it isn't, select All Messages from the SYSTEM LOG QUERIES menu on the left. If you don't see that menu, select
View ▹ Show Log List
from the menu bar.
Enter the word "Starting" (without the quotes) in the String Matching text field. You should now see log messages with the words "Starting * backup," where * represents any of the words "automatic," "manual," or "standard." Note the timestamp of the last such message. Clear the text field and scroll back in the log to that time. Select the messages timestamped from then until the end of the backup, or the end of the log if that's not clear. Copy them (command-C) to the Clipboard. Paste (command-V) into a reply to this message.
If all you see are messages that contain the word "Starting," you didn't clear the search box.
If there are runs of repeated messages, post only one example of each. Don't post many repetitions of the same message.
When posting a log extract, be selective. Don't post more than is requested.
Please do not indiscriminately dump thousands of lines from the log into this discussion.
Some personal information, such as the names of your files, may be included — anonymize before posting.