Comment 2 for bug 1986619

Hi,
I had the same problem.
First you can check if your file is "immutable" via:
#> lsattr /etc/passwd
----i-------- /etc/passwd

If is not immutable you dont have any reason for not edit via sudo, so the problem can be, like my case, the antivirus.
I kill all mcafee process multiple time, every 2 seconds, because the process try to becoming up, and then I was able to upgrade the library
I hope it will be usefull for you
Ciao