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A.5.2.7 Too many connections »
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A.5.2.6. Host 'host_name' is blocked

If you get the following error, it means that mysqld has received many connect requests from the host 'host_name' that have been interrupted in the middle: 

Host 'host_name' is blocked because of many connection errors.
Unblock with 'mysqladmin flush-hosts'

The number of interrupted connect requests allowed is determined by the value of the max_connect_errors system variable. After max_connect_errors failed requests, mysqld assumes that something is wrong (for example, that someone is trying to break in), and blocks the host from further connections until you execute a mysqladmin flush-hosts command or issue a FLUSH HOSTS statement. See Section 5.1.3, “Server System Variables”.

By default, mysqld blocks a host after 10 connection errors. You can adjust the value by starting the server like this: 

shell> mysqld_safe --max_connect_errors=10000 &

If you get this error message for a given host, you should first verify that there isn't anything wrong with TCP/IP connections from that host. If you are having network problems, it does you no good to increase the value of the max_connect_errors variable.


User Comments

Posted by Okan Cimen on May 17 2002 2:24am[Delete] [Edit]

I am running 3.23.49-nt on Win2K advanced server
w/ 2GB of RAM. When I set max_connections
parameter to 1000, connection time takes too
much. Keep it as low as you can

Posted by Roel van der Made on August 19 2004 4:42am[Delete] [Edit]

The setting of 10000 on our Debian GNU/Linux environment (4 MySQL 4.0.20 servers with 4GB ram and dual Xeon 2.8 procs) worked out very well. So the previous poster's comment does certainly not affect all platforms.
I also think the default setting of 10 is a bit low, 1000 would be more likely..

Posted by Gavin Hamill on August 31 2004 5:45am[Delete] [Edit]

This section of the manual is regarding max_connect_errors, and NOT max_connections - the previous two 'tips' are in the wrong section.

Posted by Jason Miller on September 3 2004 12:44pm[Delete] [Edit]

We ran into this problem because we use "nagios" as an availabilty monitor for our MySQL server. We were unaware of the custom nagios plugin to check mysql so we were doing a simple TCP/IP connection to the MySQL server to verify that it would receive the connection. This would eventually trigger this max-errors problem for us. However, it would only trigger it when there was no other activity on the MySQL server, making me believe that this max-errors number applies to consecutive bad connections, not bad connections intermingled with good ones.

We were not seeing any errors in the mysqld.log that led us to determine that our nagios check was the cause; luckily we realized it eventually.

Posted by Gunnar Gunnarsson on September 29 2004 6:28pm[Delete] [Edit]

A very useful link in relation to blocked hosts:
http://dev.mysql.com/doc/mysql/en/Communication_errors.html

Posted by Kovin Chan on October 5 2004 1:27am[Delete] [Edit]

I got a host to be connection blocked by server, however, those errors were not displayed in mysql error log, even log_warning is ON, wonder that should not be normal.

Posted by Christian Hammers on November 23 2004 2:38pm[Delete] [Edit]

Regarding the error log, mysqld prints errors to stderr which gets into
the mysql.err logfile. If you rotate that away all further messages will never show up as flush-logs does not reopen stderr!
(This does not apply to Debian Sarge and newer versions as they are patched to log error messages to syslog via a pipe to "logger")

Posted by Joshua Franklin on December 1 2006 8:52pm[Delete] [Edit]

We had the same problem with Nagios so I opened a bug:
http://bugs.mysql.com/bug.php?id=24761

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