Unix: Increase system's file descriptor size

This is a common problem with DB servers with heavy transactions.
The server usually throws “too many open files” errors and no new processes could be started.

check the fd size via:
$ulimit -a   # see all the kernel parameters
$ulimit -n   #see the number of open files
$ulimit -n 9000  #  set the number open files to 9000

First, in order to set this options automatically  you have to edit the etc/security/limits.conf file.
root soft  nofile 9000
root hard  nofile 65000

Second you have to add a line in the /etc/pam.d/common-session file:
$ sudo gedit /etc/pam.d/common-session #open the file in gedit
 
Then add the line:
session required pam_limits.so