mysql system database includes several
grant tables that contain information about user accounts and the
privileges held by them. This section describes those tables. For
information about other tables in the system database, see
Section 5.3, “The mysql System Database”.
Normally, to manipulate the contents of grant tables, you modify
them indirectly by using account-management statements such as
REVOKE to set up accounts and
control the privileges available to each one. See
Section 13.7.1, “Account Management Statements”. The discussion here
describes the underlying structure of the grant tables and how the
server uses their contents when interacting with clients.
Direct modification of grant tables using statements such as
DELETE is discouraged and done at
your own risk. The server is free to ignore rows that become
malformed as a result of such modifications.
As of MySQL 5.5.55, for any operation that modifies a grant table, the server checks whether the table has the expected structure and produces an error if not. mysql_upgrade must be run to update the tables to the expected structure.
mysql database tables contain grant
Each grant table contains scope columns and privilege columns:
Scope columns determine the scope of each row in the tables; that is, the context in which the row applies. For example, a
usertable row with
'bob'applies to authenticating connections made to the server from the host
thomas.loc.govby a client that specifies a user name of
bob. Similarly, a
dbtable row with
Dbcolumn values of
bobconnects from the host
thomas.loc.govto access the
columns_privtables contain scope columns indicating tables or table/column combinations to which each row applies. The
procs_privscope columns indicate the stored routine to which each row applies.
Privilege columns indicate which privileges a table row grants; that is, which operations it permits to be performed. The server combines the information in the various grant tables to form a complete description of a user's privileges. Section 6.2.5, “Access Control, Stage 2: Request Verification”, describes the rules for this.
The server uses the grant tables in the following manner:
usertable scope columns determine whether to reject or permit incoming connections. For permitted connections, any privileges granted in the
usertable indicate the user's global privileges. Any privileges granted in this table apply to all databases on the server.
dbtable scope columns determine which users can access which databases from which hosts. The privilege columns determine the permitted operations. A privilege granted at the database level applies to the database and to all objects in the database, such as tables and stored programs.
hosttable is used in conjunction with the
dbtable when you want a given
dbtable row to apply to several hosts. For example, if you want a user to be able to use a database from several hosts in your network, leave the
Hostvalue empty in the user's
dbtable row, then populate the
hosttable with a row for each of those hosts. This mechanism is described more detail in Section 6.2.5, “Access Control, Stage 2: Request Verification”.
columns_privtables are similar to the
dbtable, but are more fine-grained: They apply at the table and column levels rather than at the database level. A privilege granted at the table level applies to the table and to all its columns. A privilege granted at the column level applies only to a specific column.
procs_privtable applies to stored routines (procedures and functions). A privilege granted at the routine level applies only to a single procedure or function.
proxies_privtable indicates which users can act as proxies for other users and whether a user can grant the
PROXYprivilege to other users.
The server uses the
host tables in the
mysql database at both the first and second
stages of access control (see Section 6.2, “The MySQL Access Privilege System”).
The columns in the
db tables are shown here. The
host table is similar to the
db table but has a specialized use as described
in Section 6.2.5, “Access Control, Stage 2: Request Verification”.
Table 6.3 user and db Table Columns
|Resource control columns|
authentication_string columns store
authentication plugin and credential information.
If an account row names a plugin in the
column, the server uses it to authenticate connection attempts for
the account. It is up to the plugin whether it uses the
authentication_string column values.
plugin column for an account row is
empty, the server authenticates the account using either the
mysql_old_password plugin, depending on whether
the password hash value in the
used native hashing or the older pre-4.1 hashing method. Clients
must match the password in the
of the account row.
Prior to MySQL 5.5.11, the length of the
column was 60 characters. This was increased to 64 characters in
MySQL 5.5.11 for compatibility with the
name column. (Bug #11766610, Bug #59752)
During the second stage of access control, the server performs
request verification to ensure that each client has sufficient
privileges for each request that it issues. In addition to the
host grant tables, the server may also consult
columns_priv tables for requests that involve
tables. The latter tables provide finer privilege control at the
table and column levels. They have the columns shown in the
Table 6.4 tables_priv and columns_priv Table Columns
columns are set to the current timestamp and the
CURRENT_USER value, respectively,
but are otherwise unused.
For verification of requests that involve stored routines, the
server may consult the
procs_priv table, which
has the columns shown in the following table.
Table 6.5 procs_priv Table Columns
Routine_type column is an
ENUM column with values of
indicate the type of routine the row refers to. This column
enables privileges to be granted separately for a function and a
procedure with the same name.
columns are unused.
proxies_priv table records information
about proxy accounts. It has these columns:
For an account to be able to grant the
PROXY privilege to other accounts,
it must have a row in the
With_grant set to 1 and
Proxied_user set to indicate the account or
accounts for which the privilege can be granted. For example, the
'root'@'localhost' account created during MySQL
installation has a row in the
table that enables granting the
PROXY privilege for
''@'', that is, for all users and all hosts.
root to set up proxy users, as
well as to delegate to other accounts the authority to set up
proxy users. See Section 6.3.7, “Proxy Users”.
Scope columns in the grant tables contain strings. The default value for each is the empty string. The following table shows the number of characters permitted in each column.
Table 6.6 Grant Table Scope Column Lengths
|Column Name||Maximum Permitted Characters|
For access-checking purposes, comparisons of
Table_name values are case sensitive.
Routine_name values are not case sensitive.
host tables list each privilege in a separate
column that is declared as
'N'. In other words, each privilege can be disabled or
enabled, with the default being disabled.
tables declare the privilege columns as
SET columns. Values in these
columns can contain any combination of the privileges controlled
by the table. Only those privileges listed in the column value are
Table 6.7 Set-Type Privilege Column Values
|Table Name||Column Name||Possible Set Elements|
user table specifies administrative
privileges, such as
SHUTDOWN. Administrative operations
are operations on the server itself and are not database-specific,
so there is no reason to list these privileges in the other grant
tables. Consequently, the server need consult only the
user table to determine whether a user can
perform an administrative operation.
FILE privilege also is
specified only in the
user table. It is not an
administrative privilege as such, but a user's ability to read or
write files on the server host is independent of the database
The server reads the contents of the grant tables into memory when
it starts. You can tell it to reload the tables by issuing a
FLUSH PRIVILEGES statement or
executing a mysqladmin flush-privileges or
mysqladmin reload command. Changes to the grant
tables take effect as indicated in
Section 6.2.6, “When Privilege Changes Take Effect”.
When you modify an account, it is a good idea to verify that your
changes have the intended effect. To check the privileges for a
given account, use the
statement. For example, to determine the privileges that are
granted to an account with user name and host name values of
use this statement:
SHOW GRANTS FOR 'bob'@'pc84.example.com';