You may face the below error while switching the accounts using su command.
su: cannot create child process: Resource temporarily unavailable
If you are facing this issue that means CageFS (virtual file system per user) is not enabled for the same user due to that shell access is not available to the user's environment.
Please refer to the following commands to enable CageFS.
/usr/sbin/cagefsctl --enable accutest
Updating users ...
Run the su command again and now you shouldn't face the same issue again.
Want to know the difference between su and sudo user? Please refer to Linux > Sudo vs Su user for more details.