I started running out of space on the partition, so I investigated and found that there is a file 12GB+ in size sitting in the /usr/local/nginx and it's getting bigger.

What could this file be? Safe to delete? If not, what do you suggest I do.

root@ekv:/usr/local/nginx# du -h -x --max-depth 1

820K ./sbin
12K ./html
12G .

# lsof /usr/local/nginx/off

COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
nginx 29653 root 11w REG 8,6 12818319703 451418 /usr/local/nginx/off
nginx 29654 www-data 10w REG 8,6 12818319703 451418 /usr/local/nginx/off
nginx 29655 www-data 46w REG 8,6 12818319703 451418 /usr/local/nginx/off

Case of mistery log file. :)
Resolved.