Troubleshooting MySQL Error 1155: Resolving ER_NET_FCNTL_ERROR

Encountering an Error 1155 – SQLSTATE: 08S01 (ER_NET_FCNTL_ERROR) in MySQL indicates that there’s an issue with the fcntl() system call. This error is related to file control operations on file descriptors. Below, we will discuss various scenarios that could trigger this error and provide examples and sample code to help diagnose and fix the problem.

Understanding the Error

Before diving into solutions, it’s important to understand what fcntl() does. It performs various operations on a file descriptor, such as locking the file, changing the file’s access mode, or querying for status flags. If MySQL reports an ER_NET_FCNTL_ERROR, it’s likely due to issues with network sockets or file descriptors that MySQL uses for communication.

Diagnosing the Problem

To diagnose the issue, follow these steps:

  1. Check System Resources: Ensure that the server has enough file descriptors available. Running out of available file descriptors is a common cause for this error.
  2. Inspect MySQL Logs: Look at the MySQL error log for any additional messages that might provide context for the error.
  3. Review System Logs: System logs may contain messages related to system limits or network issues.
  4. Check Permissions: Verify that the MySQL server has the necessary file permissions, especially if it’s logging to or reading from external files.

Fixing the Error

Depending on the root cause, here are several approaches to fixing the error:

  1. Increase File Descriptors Limit:
    Modify the system limits to allow for more open file descriptors. This can be done by editing the /etc/security/limits.conf file or using the ulimit command.
   ulimit -n 10240 # Increase the number of open file descriptors
  1. Adjust MySQL Configuration:
    If the error is due to packet size, increase the max_allowed_packet size in the MySQL configuration file (my.cnf or my.ini).
  1. Repair Network Issues:
    If the error is network-related, ensure that the network is stable and that there are no firewall or router configurations blocking MySQL’s communication.
  2. File Permissions:
    Ensure that the MySQL user has the correct permissions on the files and directories it needs to access.
   chown mysql:mysql /var/lib/mysql -R # Replace with actual MySQL data directory
  1. MySQL Repair Utilities:
    Use MySQL’s built-in repair tools such as mysqlcheck to check and repair tables that might have been corrupted.
   mysqlcheck --auto-repair --check --all-databases
  1. Restart MySQL Service:
    Sometimes, simply restarting the MySQL service can resolve transient issues.
   service mysql restart


Error 1155 (ER_NET_FCNTL_ERROR) can be a sign of system resource limitations, network issues, or file permission problems. By systematically checking each potential cause and applying the appropriate fixes, you can resolve the error and restore normal operation to your MySQL server.

Remember, it’s always a good practice to backup your databases before making configuration changes or using repair utilities. If the error persists after trying these solutions, consider seeking assistance from the MySQL community or professional support.

For further reference on MySQL error codes, you can visit the official MySQL Error Codes documentation.

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