Tuesday, September 02, 2014

java.net.SocketException: Too many open files

We've recently moved our servers from windows to linux, and started getting the above error.

Its a well known scenario. Linux keeps a max number of open files limit, and we were exceeding it. Its possible to increase the limit, but first we should see if there is any process that may be causing the problem.

This is taken from http://doc.nuxeo.com/display/KB/java.net.SocketException+Too+many+open+files

Count File Descriptors in Use

Count Open File Handles
sudo lsof [-u user] | wc -l
Count File Descriptors in Kernel Memory
sudo sysctl fs.file-nr
# => The number of allocated file handles
# => The number of unused-but-allocated file handles
# => The system-wide maximum number of file handles

There is a global limit and a per user limit

Raising the Global Limit

  1. Edit /etc/sysctl.conf and add the following line:
    fs.file-max = 65536
  2. Apply the changes with:
    sudo sysctl -p /etc/sysctl.conf

Raising the per-User Limit

On some systems it is possible to use the ulimit -Hn 8192 and ulimit -Sn 4096 commands. However most of the time this is forbidden and you will get an error such as:
ulimit: open files: cannot modify limit: Operation not permitted
In those cases, you must:
  1. Edit as root the following system configuration file:
    % sudo vi /etc/security/limits.conf
  2. Modify the values for user
    user           soft    nofile          4096
    user           hard    nofile          8192
If you want to raise the limits for all users you can do instead:
*           soft    nofile          4096
*           hard    nofile          8192
To check whether changes are taken into account, open a new session w. And check that the change has been taken into account:
% su user
% ulimit -n
Here we can see that the new value has not been taken into account.
To fix this:
  1. Edit /etc/pam.d/su:
    % sudo vi /etc/pam.d/su
  2. Uncomment the line:
    session    required   pam_limits.so
    The change should now be taken into account the next time you login with your user:
    % su user
    % ulimit -n