su: cannot set user id: Resource temporarily unavailable
After searching and googling few minutes, i found a quick resolution to fixing this issue.
This is all about VPS limit.
Edit limit.conf below or change if needed.
#### add/change on these line below:
* soft nproc 2047
* hard nproc 16384
* soft nofile 2048
* hard nofile 65536
After that try to relogin using a normal access user and then try to get su -
this should fixed your issue.