I have a Backdrop site I had been building and then set aside for a few years. I was developing as a dev site (the root was in a folder in our old D6 site). 
 

We had to change our domain name, which broke a bunch of things on the D6 site, so I decided to pick up the Backdrop rebuild I had started. 
 

The BD dev site had as a domain name

dev.old_domain_name.com

The new domain is 

new_domain_name.net

I moved the BD dev-site files up to the main public_html root 

this resulted in the BD site main-page loading as expected—but no other links or pages worked—they resulted in 404 errors

I was able to login and the admin toolbar showed up, but no menu functions worked, they all returned 404s. 
 

I decided to update to BD 1.121.1 but I got an error that the database update didn’t complete because of an error. 
 

the result in any case was the same—the main page only would load, not any other pages. 
 

Are the links to subpages stored somewhere and the old references are still there?

any suggestions are much appreciated 

Brian

Comments

Have you set your $base_url in the settings.php file to the old domain, perhaps?

The problem turned out to be that I didn't move the .htaccess file when I moved the files from the old directory (using Transmit, I didn't have 'show hidden files' on)

That makes sense! Thanks for following up.