Fix Host ‘IP’ is blocked because of many connection errors on MySQL/MariaDB

$ mysql -u foo -h 172.16.5.100 -p dbnmame

ERROR 1129 (HY000): Host ‘172.16.5.100’ is blocked because of many connection errors; unblock with ‘mysqladmin flush-hosts’

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How to find out current value of max_connections

I am trying to login to my mysql/mysqld server using the following Unix command:But greeted with the following error on screen:How do I fix this problem on a Linux or Unix-like system?The number of connections permitted is controlled by the MySQL/MariaDB max_connections system variable. The default value is 151 to improve performance when MySQL is used with the Web server. You might run into a problem if you are running a high trafficked web site or MariaDB server in clustered mode or using a Galera master to master DB cluster . If you need to support more connections, you should set a more substantial value for this variable.

Type the following mysql command:

$ mysql -u root -p

Now issue the following sql command:

mysql> show variables like "max_connections";

Sample outputs:

+-----------------+--------+ | Variable_name | Value | +-----------------+--------+ | max_connections | 151 | +-----------------+--------+ 1 row in set (0.00 sec)

How do I increase max_connections value?

Edit my.cnf or mariadb.conf.d/50-server.cnf in /etc/ directory using a text editor such as vi command or nano command:

$ sudo vim /etc/mariadb.conf.d/50-server.cnf

Add/append/edit the following line under [mysqld] section (say set value to 1000. Max limit is 100000):

max_connections = 1000

Save and close the file. Next, restart the mysqld service, run:

$ sudo systemctl restart mysql

If you are using a CentOS/RHEL/Fedora/Oracle/Scientific Linux, run:

$ sudo systemctl restart mysqld

If you are using a FreeBSD unix, run the following to restart the system:

$ sudo /usr/local/etc/rc.d/mysql-server restart

Verify new limits with the following command:

$ mysql -u root -p -e 'show variables like "max_connections";'



A note about mysqladmin command

To flush all cached hosts and remove this limit run the following bash command $ mysqladmin flush-hosts

OR pass username and prompt for a password:

$ mysqladmin -u root -p flush-hosts

A note about “Too many open files” error

You need to changes the number of file descriptors available to mysqld if you get the error. To see current FD limits, run:

$ mysql -u root -p -e 'show variables like "open_files_limit";'

Sample outputs:

Enter password: +------------------+--------+ | Variable_name | Value | +------------------+--------+ | open_files_limit | 500005 | +------------------+--------+

Again edit my.cnf if limit is too small and getting an error in your log file:

$ sudo vi my.cnf

OR

$ sudo vim /etc/mariadb.conf.d/50-server.cnf

Set the value as per requirements in in [mysqld] section

open_files_limit = 1024000

Save and close the file. Make sure you restart the mysqld as described above. If you are using GNU/Linux systemd based distro such as RHEL/CentOS 7, create a file named:

$ sudo vi /etc/systemd/system/mysqld.service

Append the following:

[Service] User=mysql

Group=mysql

LimitNOFILE=1024000

Restart needed services:

$ sudo systemctl daemon-reload

$ sudo systemctl restart mysqld

Older Linux distro must edit the /etc/security/limits.conf file.