Description of problem: Running squid with large cache_dir is problematic due to small limit of open files. Please increase LimitNOFILE in default systemd.service file. Version-Release number of selected component (if applicable): squid-3.2.0.14-1.fc16.i686 How reproducible: always Actual results: error opening files Additional info: This fixed my problems: [Service] Type=forking LimitNOFILE=16384 There are also other services in fedora, which changes default ulimits. I think squid is one of most file opening process.