Maximum number of opened files allowed: cat /proc/sys/fs/file-nr (if run on OVZ VPS, it shows limit of the host server)
# cat /proc/sys/fs/file-nr
1632 0 2451492
(1632 files opened opened out of 2451492 maximum allowed)

A method) echo 1234567 > /proc/sys/fs/file-max
B method) add or update variable fs.file-max in /etc/sysctl.conf:
fs.file-max = 1234567
and run: sysctl -p

If it is wrong, please describe how it is correct.