Change maximum number of file descriptors in Linux

from: https://www.cyberciti.biz/faq/linux-increase-the-maximum-number-of-open-files/

display maximum number of open file descriptors:
cat /proc/sys/fs/file-max

To see the hard and soft values, issue the command as follows:
# ulimit -Hn
# ulimit -Sn

increase the maximum number of open files by setting a new value in kernel variable /proc/sys/fs/file-max as follows (login as the root):
# sysctl -w fs.file-max=100000
Above command forces the limit to 100000 files. You need to edit /etc/sysctl.conf file and put following line so that after reboot the setting will remain as it is:
# vi /etc/sysctl.conf
Append a config directive as follows:
fs.file-max = 100000
Save and close the file. Users need to log out and log back in again to changes take effect or just type the following command:
# sysctl -p
Verify your settings with command:
# cat /proc/sys/fs/file-max
OR
# sysctl fs.file-max

User Level FD Limits

The above procedure sets system-wide file descriptors (FD) limits. However, you can limit httpd (or any other users) user to specific limits by editing /etc/security/limits.conf file, enter:
# vi /etc/security/limits.conf
Set httpd user soft and hard limits as follows:
httpd soft nofile 4096
httpd hard nofile 10240

Save and close the file. To see limits, enter:
# su - httpd
$ ulimit -Hn
$ ulimit -Sn

A note about RHEL/CentOS/Fedora/Scientific Linux users

Edit /etc/pam.d/login file and add/modify the following line (make sure you get pam_limts.so):

session required pam_limits.so
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