>I don't see any logic here. Are you sure your squid is started not by root? >Is replacing 'root' by 'squid' or '*' solves issue as well? When I manually start service by root, there is no file descriptor warning and squid works as normal. But when the system boots up and starts the service automatically, squid runs out of FD. I've tested different the following settings without any luck. Every time that the box reboots, I have to login and restart service manually. root soft nofile 65000 root hard nofile 65000 proxy soft nofile 65000 proxy hard nofile 65000 squid soft nofile 65000 squid hard nofile 65000 * soft nofile 65000 * hard nofile 65000 It seems these settings only works if the user logins to system. My squid user is "proxy"(I configured it at the time of compile). Maybe some useful info: OS:Ubuntu 12.04 # ulimit -n 65000 # squidclient mgr:info | grep 'file descri' Maximum number of file descriptors: 65536 Available number of file descriptors: 65527 Reserved number of file descriptors: 100