CLOSE_WAITはデフォルトで2時間ほど残ってしまうようです。
# vi /etc/sysctl.conf net.ipv4.tcp_keepalive_time = 10 net.ipv4.tcp_keepalive_probes = 2 net.ipv4.tcp_keepalive_intvl = 3
設定を反映
# sysctl -w
http://hirofukami.com/2008/08/11/close-wait/
http://luozengbin.github.io/blog/2014-10-29-%5B%E3%83%A1%E3%83%A2%5Dapache%E3%81%A7backend%E3%81%A8%E3%81%AEkeepalive%E3%82%92off%E3%81%AB%E3%81%99%E3%82%8B.html