MySQL 9.5 Reference Manual Including MySQL NDB Cluster 9.5
MySQL stores accounts in the user table of the
mysql system database. An account is defined in
terms of a user name and the client host or hosts from which the
user can connect to the server. For information about account
representation in the user table, see
Section 8.2.3, “Grant Tables”.
An account may also have authentication credentials such as a password. The credentials are handled by the account authentication plugin. MySQL supports multiple authentication plugins. Some of them use built-in authentication methods, whereas others enable authentication using external authentication methods. See Section 8.2.17, “Pluggable Authentication”.
There are several distinctions between the way user names and passwords are used by MySQL and your operating system:
User names, as used by MySQL for authentication purposes, have
nothing to do with user names (login names) as used by Windows
or Unix. On Unix, most MySQL clients by default try to log in
using the current Unix user name as the MySQL user name, but
that is for convenience only. The default can be overridden
easily, because client programs permit any user name to be
specified with a -u or
--user option. This means that anyone can
attempt to connect to the server using any user name, so you
cannot make a database secure in any way unless all MySQL
accounts have passwords. Anyone who specifies a user name for
an account that has no password can connect successfully to
the server.
MySQL user names are up to 32 characters long. Operating system user names may have a different maximum length.
The MySQL user name length limit is hardcoded in MySQL
servers and clients, and trying to circumvent it by
modifying the definitions of the tables in the
mysql database does not
work.
You should never alter the structure of tables in the
mysql database in any manner whatsoever
except by means of the procedure that is described in
Chapter 3, Upgrading MySQL. Attempting to redefine the
MySQL system tables in any other fashion results in
undefined and unsupported behavior. The server is free to
ignore rows that become malformed as a result of such
modifications.
To authenticate client connections for accounts that use
built-in authentication methods, the server uses passwords
stored in the user table. These passwords
are distinct from passwords for logging in to your operating
system. There is no necessary connection between the
“external” password you use to log in to a
Windows or Unix machine and the password you use to access the
MySQL server on that machine.
If the server authenticates a client using some other plugin,
the authentication method that the plugin implements may or
may not use a password stored in the user
table. In this case, it is possible that an external password
is also used to authenticate to the MySQL server.
Passwords stored in the user table are
encrypted using plugin-specific algorithms.
If the user name and password contain only ASCII characters,
it is possible to connect to the server regardless of
character set settings. To enable connections when the user
name or password contain non-ASCII characters, client
applications should call the
mysql_options() C API function
with the MYSQL_SET_CHARSET_NAME option and
appropriate character set name as arguments. This causes
authentication to take place using the specified character
set. Otherwise, authentication fails unless the server default
character set is the same as the encoding in the
authentication defaults.
Standard MySQL client programs support a
--default-character-set option that causes
mysql_options() to be called
as just described. In addition, character set autodetection is
supported as described in
Section 12.4, “Connection Character Sets and Collations”. For programs that use a
connector that is not based on the C API, the connector may
provide an equivalent to
mysql_options() that can be
used instead. Check the connector documentation.
The preceding notes do not apply for ucs2,
utf16, and utf32, which
are not permitted as client character sets.
The MySQL installation process populates the grant tables with an
initial root account, as described in
Section 2.9.4, “Securing the Initial MySQL Account”, which also discusses how to
assign a password to it. Thereafter, you normally set up, modify,
and remove MySQL accounts using statements such as
CREATE USER,
DROP USER,
GRANT, and
REVOKE. See
Section 8.2.8, “Adding Accounts, Assigning Privileges, and Dropping Accounts”, and
Section 15.7.1, “Account Management Statements”.
To connect to a MySQL server with a command-line client, specify user name and password options as necessary for the account that you want to use:
$> mysql --user=finley --password db_name
If you prefer short options, the command looks like this:
$> mysql -u finley -p db_name
If you omit the password value following the
--password or -p
option on the command line (as just shown), the client prompts for
one. Alternatively, the password can be specified on the command
line:
$>mysql --user=finley --password=$>passworddb_namemysql -u finley -ppassworddb_name
If you use the -p option, there must be
no space between -p and the
following password value.
Specifying a password on the command line should be considered insecure. See Section 8.1.2.1, “End-User Guidelines for Password Security”. To avoid giving the password on the command line, use an option file or a login path file. See Section 6.2.2.2, “Using Option Files”, and Section 6.6.7, “mysql_config_editor — MySQL Configuration Utility”.
For additional information about specifying user names, passwords, and other connection parameters, see Section 6.2.4, “Connecting to the MySQL Server Using Command Options”.