How do you tell which host is close to being blocked in MySQL?
Actually, you should raise the max_connect_errors way beyond the default of 10.

The range is 1-18446744073709547520. I would set it to 1000 for now.

However, you have a bigger problem. mysqladmin requires you connect to mysqld before it does anything. If max_connect_errors is reached too quickly, you cannot make mysqladmin do anything at that point. Even a cron job will fail in this respect.

Since you are using MySQL 5.5, your best option is create a scheduled event within the MySQL Instance to go off every 5 minutes that will only do one thing: run FLUSH HOSTS.

I just did this in MySQL 5.5.12 on my PC

mysql&gt; use test
Database changed
mysql&gt; CREATE EVENT ev ON SCHEDULE
    -&gt;       EVERY 5 MINUTE
    -&gt; STARTS (NOW() + INTERVAL 1 MINUTE)
    -&gt; DO FLUSH HOSTS;
Query OK, 0 rows affected (0.02 sec)

mysql&gt;


Great, no complaints from mysqld. Of course, I arbitrarily chose 5 minutes. You can choose whatever schedule you prefer.

Give it a Try !!!

UPDATE 2011-08-25 11:22 EDT

For everybody using release of MySQL prior to 5.1, I have a worthwhile suggestion:

Write a perl script that keeps an open connection, making it heartbeat itself by retrieving something (i.e., uptime, aborted_connects, etc) and every 10 minutes kicking out FLUSH HOSTS. Whatever user you connect as, make sure it has RELOAD privilege.

For example: run this command:

GRANT RELOAD on *.* to 'whateveruser'@'localhost' identified by 'whateverpassword';


Here is a perl script I call heartbeat.pl to do this using that user and password:

#!/usr/bin/perl

use DBI;
use DBD::mysql;

my ($SLEEP_TIME_INTERVAL,$HEARTBEAT_CYCLE) = @ARGV;

$check_replication = 1;

$username = "whateveruser";
$password = "whateverpassword";

$MYSQL_HEARTBEAT_FILE = "/tmp/MySQLHeartBeat.txt";
$MYSQL_FLATLINE_FILE  = "/tmp/MySQLFlatLine.txt";

$MYSQL_PROCESSLIST_FILE = "/tmp/MySQL_Processlist.txt";

if ( $SLEEP_TIME_INTERVAL == 0 )
{
        open(fh_output,"&gt; $MYSQL_FLATLINE_FILE") or die "Can't Find File $MYSQL_HEARTBEAT_FILE\n$!\n";
        printf fh_output "DONE !!!\n";
        close fh_output;
        exit 0;
}

$db = DBI-&gt;connect("DBI:mysql:information_schema;host=127.0.0.1",$username,$password)
or die "Cannot connect to the DB information_schema\n",$DBI-&gt;errstr(),"\n";

$st_globalstatus = $db-&gt;prepare("SHOW GLOBAL STATUS") or die "Cannot Prepare SQL Statement\n",$DBI-&gt;errstr(),"\n";
$st_flush_hosts  = $db-&gt;prepare("FLUSH HOSTS")        or die "Cannot Prepare SQL Statement\n",$DBI-&gt;errstr(),"\n";

$heartbeat_count = 0;
$my_heart_is_beating = 1;
while ( $my_heart_is_beating )
{
        $st_globalstatus-&gt;execute() or die "Cannot Execute SQL Statement\n",$DBI-&gt;errstr(),"\n";
        {
                $StatusCount  = 0;
                while ( my $row = $st_globalstatus-&gt;fetchrow_hashref() )
                {
                        my $uptime = $row-&gt;{Value};
                }
                $st_globalstatus-&gt;finish();
                open(fh_output,"&gt; $MYSQL_HEARTBEAT_FILE") or die "Can't Find File $MYSQL_HEARTBEAT_FILE\n$!\n";
                printf fh_output "%s : %s\n",$uptime;
                close fh_output;
        }
        for ($i = 0; $i &lt; $SLEEP_TIME_INTERVAL; $i++)
        {
                if ( -f $MYSQL_FLATLINE_FILE )
                {
                        unlink $MYSQL_HEARTBEAT_FILE;
                        unlink $MYSQL_FLATLINE_FILE;
                        $my_heart_is_beating = 0;
                }
                sleep 1;
        }
        $heartbeat_count++;
        if ( $heartbeat_count == $HEARTBEAT_CYCLE )
        {
                $heartbeat_count = 0;
                $st_flush_hosts-&gt;execute();
        }
}

$db-&gt;disconnect();


In the OS, call the perl script to heartbeat every 6 seconds. When it heartbeats 100 times, that 600 seconds (10 minutes), make it run FLUSH HOSTS. Call it like this:

nohup perl heartbeat.pl 6 100 &amp;


Here are other schedules:

nohup perl heartbeat.pl  6  50 &amp; (heartbeat every  6 sec,FLUSH HOSTS every 5 minutes)
nohup perl heartbeat.pl 10 360 &amp; (heartbeat every 10 sec,FLUSH HOSTS every 1 hour)
nohup perl heartbeat.pl 60 180 &amp; (heartbeat every 60 sec,FLUSH HOSTS every 3 hours)


To stop the program, run this:

perl heartbeat.pl