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MySQL values open_files_limit and max_connections are not applied

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Robert Asilbekov
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Plesk for Linux kb: technical ABT: Group B

Applicable to:

  • Plesk for Linux

Symptoms

  • The value of max_connections changes to 214 automatically after some time, although the value itself is defined in my.cnf:

    # grep -i 'max_connections' /etc/my.cnf
    max_connections=2048

    # plesk db "SHOW GLOBAL VARIABLES LIKE 'max_connections' \G"
    *************************** 1. row ***************************
    Variable_name: max_connections
    Value: 214

  • The value of open_files_limit is reset after system updates are installed.

  • In the log file /var/log/mysqld.log the following records can be found:

    CONFIG_TEXT: [Warning] Changed limits: max_open_files: 1024 max_connections: 214 table_cache: 400

  • When restoring a MySQL backup, the following error is shown:

    Warning: mysql "databasename"
    Not all the data was backed up into [...]/databasename_1 successfully. mysqldump: Got error: 23: Out of resources when opening file '[...]' (Errcode: 24 - Too many open files) when using LOCK TABLES

  • Unable to export database in Plesk:

    PLESK_ERROR: Unable to export a dump of databasename:
    mysqldump: Got error: 1016: "Can't open file: './databasename/table.frm' (errno: 24)" when using LOCK TABLES

Cause

Default open_files_limit for MySQL has been reached.

Resolution

Connect to the server via SSH and adjust open_files_limit for the MySQL service as below.

Note: This article may require additional administrative knowledge to apply. If any help required, contact server’s administrator or hosting support.

On systemd-based systems (RHEL/CentOS/CloudLunix 7 and above, Ubuntu 16.04 and above, Debian 8 and above)

  1. Find out whether MySQL, or MariaDB service is used:

    # systemctl list-unit-files | grep -E 'mysql|mariadb'
    mariadb.service enabled

  2. Create an override for the service file from the previous step:

    # systemctl edit mariadb.service

    Note: In case mysql.service, or mysqld.service was displayed on the previous step, replace "mariadb.service" with it.

  3. Add the following content to the opened text editor and save the file:

    CONFIG_TEXT: [Service]
    LimitNOFILE=4096

    Note: Value might be increased if required, 4096 is only a suggested value.
    In case "LimitNOFILE=Infinity" limit should be set by "open_files_limit" directive in "[mysqld]" section of "my.cnf" file.

  4. Restart the MySQL/MariaDB server:

    # systemctl restart mysql mysqld mariadb 2>/dev/null

On System V/Upstart systems (Ubuntu 14.04, RHEL/CentOS/CloudLinux 6)

For Debian-based distributions:

  1. Add the following lines in /etc/security/limits.conf:

    CONFIG_TEXT: mysql soft nofile 4096
    mysql hard nofile 4096

  2. Add the following to the end of file into /etc/pam.d/common-session :

    CONFIG_TEXT: session required pam_limits.so

  3. Add the following to the end of file into /etc/pam.d/common-session-noninteractive:

    CONFIG_TEXT: session required pam_limits.so

  4. Add the following line in /etc/mysql/my.cnf and under the [mysqld] section:

    CONFIG_TEXT: open_files_limit = 4096

  5. Restart the MySQL service:

    # service mysql restart

For RHEL-based distributions:

  1. Add the following line in /etc/sysctl.conf:

    CONFIG_TEXT: fs.file-max = 65536

  2. Edit the file /etc/security/limits.conf and add lines:

    CONFIG_TEXT: * soft nproc 40960
    * hard nproc 40960
    * soft nofile 40960
    * hard nofile 40960

  3. Edit the file /etc/security/limits.d/90-nproc.conf and add lines:

    CONFIG_TEXT: * soft nproc 40960
    * hard nproc 40960
    * soft nofile 40960
    * hard nofile 40960

  4. Add the following line in /etc/my.cnf and under the [mysqld] section:

    CONFIG_TEXT: open_files_limit = 4096

  5. Restart the MySQL service:

    # service mariadb restart

Comments

3 comments

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  • Avatar
    nisamudeen plackal

    Ubuntu has moved from Upstart to Systemd  from version 15.04 and no longer respects the limits in /etc/security/limits.conf for system services. These limits now apply only to user sessions.

    The limits for the MySQL service are defined in the Systemd configuration file, which you should copy from its default location into /etc/systemd and then edit the copy.

    sudo cp /lib/systemd/system/mysql.service /etc/systemd/system/
    sudo vim /etc/systemd/system/mysql.service # or your editor of choice

    Add the following lines to the bottom of the file:

    LimitNOFILE=infinity
    LimitMEMLOCK=infinity

    You could also set a numeric limit, eg LimitNOFILE=4096

    Now reload the Systemd configuration with:

    sudo systemctl daemon-reload

    Restart MySQL and it should now obey the max_connections directive.

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  • Avatar
    Andrey Ivanov

    Hello nisamudeen,

    Thank you for your reply! A section regarding systemd systems was added accordingly.

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  • Avatar
    sanel kape

    Yes it work,after setting params in /etc/systemd/system/mysql.service ,this is for newer ubuntu versions

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