Setfacl

Common arguments

-b remove all ACL entries

What is that weird plus sign in ls -l output?

It means the file has ACLs associated with it.

-rw-------+ 1 root  root   8569 Sep 21 01:43 file.txt

To remove them all:

setfacl -b file.txt

Now it's gone.

-rw------- 1 root  root   8569 Sep 21 01:43 file.txt