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Im running an ubuntu server 16.04.5. System was working properly up to until a few days ago. Then yesterday I found out that I cannot login from the local keyboard. System behaves strangely....it takes the username but not the password. It looks like the enter key is stuck (its not) sending an empty password. After a few loops it resets asking for username. Login works via ssh and the problem also disappears once booting with previous kernel (4.4.0-151-genric). Any help??

sourfou
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    Welcome to Ask Ubuntu. I'd firstly check the keyboard itself (plus connection). Unplug it, re-plug it in or try a different keyboard. Yes if it only occurs on a specific kernel it's likely a software issue, but if hardware related (esp. dying component or poor/dirty connectors) it can work sometimes, other times not & co-incidence can give wrong impressions... – guiverc Feb 06 '19 at 00:31
  • the keyboard is ok. The problem was a known issue with some kernels. Setting as default an unaffected kernel solved the problem. Thx for feedback. – sourfou Feb 06 '19 at 15:29
  • See also: https://askubuntu.com/questions/1113704/tty-doesnt-wait-for-password – Nathaniel M. Beaver Feb 20 '19 at 16:37

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It's a known bug:

console login loop after entering username followed by RETURN

https://bugs.launchpad.net/ubuntu/+source/shadow/+bug/1812095

Userspace break as a result of missing patch backport

https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1813873

Check your kernel version to see if you're affected. 4.15.0-43-generic is good, 4.15.0-44-generic and 4.15.0-45-generic are bad.

$ uname -r
4.15.0-45-generic
Nathaniel M. Beaver
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  • yeah thx for the help. Its the kernel issue u mention. Also confirming kernel 4.4.0-141 is good but 4.4.0-142 is bad for ubuntu server 16.04.5. Setting the former as default in grub, solved the issue. – sourfou Feb 06 '19 at 15:23