Do you have the open files limit set sufficiently high?
ulimit -n
should show 16k or higher.
That shouldn't be the problem - nofile is set to 32k in the upstart script.
My setup:
Ubuntu 12.04 LTS (kernel 3.2.0) w/Python 2.7.3; latest Electrum server from git; leveldb 1.9.0; plyvel 0.8
What does the ulimit command show for the userid running the server, though? On most Linuxes, max open files is set to 1024, and this limit can
not be raised by non-root users.
You probably need to add a line to /etc/security/limits.conf to give your server user a higher soft/hard limit. ie:
electrum soft nofile 16384
electrum hard nofile 16384
grnbrg.