A.2.3 Client does not support authentication protocol

MySQL 4.1 and up uses an authentication protocol based on a password hashing algorithm that is incompatible with that used by older clients. If you upgrade the server to 4.1, attempts to connect to it with an older client may fail with the following message:

shell> mysql
Client does not support authentication protocol requested
by server; consider upgrading MySQL client

To solve this problem, you should use one of the following approaches:

• Upgrade all client programs to use a 4.1.1 or newer client library.

• When connecting to the server with a pre-4.1 client program, use an account that still has a pre-4.1-style password.

• Reset the password to pre-4.1 style for each user that needs to use a pre-4.1 client program. This can be done using the SET PASSWORD statement and the OLD_PASSWORD() function:

  mysql> SET PASSWORD FOR
    -> 'some_user'@'some_host' = OLD_PASSWORD('newpwd');

  Alternatively, use UPDATE and FLUSH PRIVILEGES:

  mysql> UPDATE mysql.user SET Password = OLD_PASSWORD('newpwd')
    -> WHERE Host = 'some_host' AND User = 'some_user';
  mysql> FLUSH PRIVILEGES;

  Substitute the password you want to use for "newpwd" in the preceding examples. MySQL cannot tell you what the original password was, so you'll need to pick a new one.

• Tell the server to use the older password hashing algorithm:

  1. Start mysqld with the --old-passwords option.

  2. Assign an old-format password to each account that has had its password updated to the longer 4.1 format. You can identify these accounts with the following query:

     mysql> SELECT Host, User, Password FROM mysql.user
                  -> WHERE LENGTH(Password) > 16;

  3. For each account record displayed by the query, use the Host and User values and assign a password using the OLD_PASSWORD() function and either SET PASSWORD or UPDATE, as described earlier.

For additional background on password hashing and authentication, see Section 4.4.9, "Password Hashing in MySQL 4.1."

A.2.4 Password Fails When Entered Interactively

MySQL client programs prompt for a password when invoked with a --password or -p option that has no following password value:

shell> mysql -u user_name -p
Enter password:

On some systems, you may find that your password works when specified in an option file or on the command line, but not when you enter it interactively at the Enter password: prompt. This occurs when the library provided by the system to read passwords limits password values to a small number of characters (typically eight). That is a problem with the system library, not with MySQL. To work around it, change your MySQL password to a value that is eight or fewer characters long, or put your password in an option file.

A.2.5 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 4.2.3, "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 will do you no good to increase the value of the max_connect_errors variable.

A.2.6 Too many connections

If you get a Too many connections error when you try to connect to the mysqld server, this means that all available connections already are used by other clients.

The number of connections allowed is controlled by the max_connections system variable. Its default value is 100. If you need to support more connections, you should restart mysqld with a larger value for this variable.

mysqld actually allows max_connections+1 clients to connect. The extra connection is reserved for use by accounts that have the SUPER privilege. By granting the SUPER privilege to administrators and not to normal users (who should not need it), an administrator can connect to the server and use SHOW PROCESSLIST to diagnose problems even if the maximum number of unprivileged clients already are connected.

The maximum number of connections MySQL can support depends on the quality of the thread library on a given platform. Linux or Solaris should be able to support 500-1000 simultaneous connections, depending on how much RAM you have and what your clients are doing.  

This chapter is from MySQL Administrator's Guide, by MySQL AB. (Sams, 2004, ISBN: 0672326345). Check it out at your favorite bookstore today. Buy this book now.

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