The Directory Proxy Server allows for an unlimited number of connections by default but is restricted by the file descriptor limit on the operating system. Many Linux distributions have a default file descriptor limit of 1024 per process, which may be too low for the server if it needs to handle a large number of concurrent connections.

Once the operating system limit is set, the number of file descriptors that the server will use can be configured by either using a NUM_FILE_DESCRIPTORS environment variable, or by creating a config/num-file-descriptors file with a single line such as, NUM_FILE_DESCRIPTORS=12345. If these are not set, the default of 65535 is used. This is strictly optional if wanting to ensure that the server shuts down safely prior to reaching the file descriptor limit.

  1. Display the current hard limit of your system. The hard limit is the maximum server limit that can be set without tuning the kernel parameters in the proc file system.
    ulimit -aH
  2. Edit the /etc/sysctl.conf file. If there is a line that sets the value of the fs.file-max property, make sure its value is set to at least 65535. If there is no line that sets a value for this property, add the following to the end of the file:
    fs.file-max = 65535
  3. Edit the /etc/security/limits.conf file. If the file has lines that sets the soft and hard limits for the number of file descriptors, make sure the values are set to 65535. If the lines are not present, add the following lines to the end of the file (before “#End of file”). Also note that you should insert a tab, rather than spaces, between the columns.
    * soft nofile 65535
    * hard nofile 65535
  4. Reboot your system, and then use the ulimit command to verify that the file descriptor limit is set to 65535.
    # ulimit -n
Note: For RedHat 7 or later, modify the 20-nproc.conf file to set both the open files and max user processes limits:

 Add or edit the following lines if they do not already exist:

 *          soft    nproc     65536
 *          soft    nofile    65536
 *          hard    nproc     65536
 *          hard    nofile    65536
 root       soft    nproc     unlimited