If you're using Selinux on gentoo (or any linux where you set up the /etc/fstab entry for /dev/pts yourself), you should consider using mode=1622. Most of the time, you'll get an error like

get_pty: not enough ptys
when starting X or running sshd, etc. This is because you don't have write access to /dev/pts if you've set up the mount to be mode=620, which a lot of documents do (like the Gentoo installer).