I'm connecting via SSH to a Centos 7 machine. I have a user that cannot perform any command as super user. If I do:

$ sudo ls /

I get the error: "sudo: unable to fork: Resource temporarily unavailable". The user is a member both of the sudo and the admin groups. When I enter the groups command, I get: "myuser sudo admin", and my /etc/sudoers file has the lines:

# Members of the admin group may gain root privileges
%admin ALL=(ALL) ALL

# Allow members of group sudo to execute any command
%sudo   ALL=(ALL:ALL) ALL

So what could be the problem? Thanks