MySQL values open_files_limit and max_connections are not applied – Plesk Help Center

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'"
| max_connections                                   | 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:

[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

Cause

open_files_limit for MySQL has been reached.

Resolution

Adjust open_files_limit for the MySQL service. For that, check the current value:

# plesk db "SHOW GLOBAL VARIABLES LIKE 'open_files_limit'"
+------------------+-------+
| Variable_name    | Value |
+------------------+-------+
| open_files_limit | 1024  |
+------------------+-------+

On systemd systems:

Create limit_nofile.conf file:
- For Debian-based distributions:
  
  Create /lib/systemd/system/mysql.service.d/limit_nofile.conf file with the following content:
```
# cat /lib/systemd/system/mysql.service.d/limit_nofile.conf
[Service]
LimitNOFILE=4096
```
- For RHEL-based distributions:
  
  Create /usr/lib/systemd/system/mariadb.service.d/limit_nofile.conf file with the following content:
```
# cat /usr/lib/systemd/system/mariadb.service.d/limit_nofile.conf
[Service]
LimitNOFILE=4096
```

Reload daemons and restart MySQL service:

# systemctl daemon-reload
# systemctl restart mysql

On System V systems:

For Debian-based distributions:
1. Add the following lines in /etc/security/limits.conf:
```
mysql             soft    nofile           4096
mysql             hard    nofile           4096
```
2. Add the following to the end of file into /etc/pam.d/common-session :
```
session required pam_limits.so
```
3. Add the following to the end of file into /etc/pam.d/common-session-noninteractive:
```
session required pam_limits.so
```
4. Add the following line in /etc/mysql/my.cnf and under the [mysqld] section:
```
open_files_limit = 4096
```
5. Restart the MySQL service.

For RHEL-based distributions:

Add the following line in /etc/sysctl.conf:
```
fs.file-max = 65536
```

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

*          soft     nproc          40960
*          hard     nproc          40960
*          soft     nofile         40960
*          hard     nofile         40960

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

*          soft     nproc          40960
*          hard     nproc          40960
*          soft     nofile         40960
*          hard     nofile         40960

Add the following line in /etc/my.cnf and under the [mysqld] section:
```
open_files_limit = 4096
```
Restart the MySQL service.

Comments

3 comments

nisamudeen plackal May 19, 2017 00:47

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.

0

Andrey Ivanov May 24, 2017 13:39

Hello nisamudeen,

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

0

sanel kape July 07, 2017 13:36

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

0