• MySQL 5.1 Reference Manual :: 5 MySQL Server Administration :: 5.4 The MySQL Access Privilege System :: 5.4.2 Privilege System Grant Tables

  • 5.4.2. Privilege System Grant Tables

    Normally, you manipulate the contents of the grant tables in the mysql database indirectly by using statements such as GRANT and REVOKE to set up accounts and control the privileges available to each one. See Section 12.4.1, “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.

    Some tables in the mysql database do not hold grant information and are discussed elsewhere:

    Each grant table contains scope columns and privilege columns:

    • Scope columns determine the scope of each row (entry) in the tables; that is, the context in which the row applies. For example, a user table row with Host and User values of 'thomas.loc.gov' and 'bob' would be used for authenticating connections made to the server from the host thomas.loc.gov by a client that specifies a user name of bob. Similarly, a db table row with Host, User, and Db column values of 'thomas.loc.gov', 'bob' and 'reports' would be used when bob connects from the host thomas.loc.gov to access the reports database. The tables_priv and columns_priv tables contain scope columns indicating tables or table/column combinations to which each row applies. The procs_priv scope columns indicate the stored routine to which each row applies.

    • Privilege columns indicate which privileges are granted by a table row; that is, what operations can be performed. The server combines the information in the various grant tables to form a complete description of a user's privileges. Section 5.4.5, “Access Control, Stage 2: Request Verification”, describes the rules that are used to do this.

    The server uses the grant tables in the following manner:

    • The user table scope columns determine whether to reject or allow incoming connections. For allowed connections, any privileges granted in the user table indicate the user's global (superuser) privileges. Any privilege granted in this table applies to all databases on the server.

      Note

      Because any global privilege is considered a privilege for all databases, any global privilege enables a user to see all database names with SHOW DATABASES or by examining the SCHEMATA table of INFORMATION_SCHEMA.

    • The db table scope columns determine which users can access which databases from which hosts. The privilege columns determine which operations are allowed. A privilege granted at the database level applies to the database and to all objects in the database, such as tables and stored programs.

    • The host table is used in conjunction with the db table when you want a given db table 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 Host value empty in the user's db table row, then populate the host table with a row for each of those hosts. This mechanism is described more detail in Section 5.4.5, “Access Control, Stage 2: Request Verification”.

      Note

      The host table must be modified directly with statements such as INSERT, UPDATE, and DELETE. It is not affected by statements such as GRANT and REVOKE that modify the grant tables indirectly. Most MySQL installations need not use this table at all.

    • The tables_priv and columns_priv tables are similar to the db table, 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.

    • The procs_priv table applies to stored routines. A privilege granted at the routine level applies only to a single routine.

    The server uses the user, db, and host tables in the mysql database at both the first and second stages of access control (see Section 5.4, “The MySQL Access Privilege System”). The columns in the user and db tables are shown here. The host table is similar to the db table but has a specialized use as described in Section 5.4.5, “Access Control, Stage 2: Request Verification”.

    Table Name user db
    Scope columns Host Host
      User Db
      Password User
    Privilege columns Select_priv Select_priv
      Insert_priv Insert_priv
      Update_priv Update_priv
      Delete_priv Delete_priv
      Index_priv Index_priv
      Alter_priv Alter_priv
      Create_priv Create_priv
      Drop_priv Drop_priv
      Grant_priv Grant_priv
      Create_view_priv Create_view_priv
      Show_view_priv Show_view_priv
      Create_routine_priv Create_routine_priv
      Alter_routine_priv Alter_routine_priv
      Execute_priv Execute_priv
      Trigger_priv Trigger_priv
      Event_priv Event_priv
      Create_tmp_table_priv Create_tmp_table_priv
      Lock_tables_priv Lock_tables_priv
      References_priv References_priv
      Reload_priv  
      Shutdown_priv  
      Process_priv  
      File_priv  
      Show_db_priv  
      Super_priv  
      Repl_slave_priv  
      Repl_client_priv  
      Create_user_priv  
    Security columns ssl_type  
      ssl_cipher  
      x509_issuer  
      x509_subject  
    Resource control columns max_questions  
      max_updates  
      max_connections  
      max_user_connections  

    The Event_priv and Trigger_priv columns were added in MySQL 5.1.6.

    During the second stage of access control, the server performs request verification to make sure that each client has sufficient privileges for each request that it issues. In addition to the user, db, and host grant tables, the server may also consult the tables_priv and 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 following table.

    Table Name tables_priv columns_priv
    Scope columns Host Host
      Db Db
      User User
      Table_name Table_name
        Column_name
    Privilege columns Table_priv Column_priv
      Column_priv  
    Other columns Timestamp Timestamp
      Grantor  

    The Timestamp and Grantor columns currently are unused and are discussed no further here.

    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 Name procs_priv
    Scope columns Host
      Db
      User
      Routine_name
      Routine_type
    Privilege columns Proc_priv
    Other columns Timestamp
      Grantor

    The Routine_type column is an ENUM column with values of 'FUNCTION' or 'PROCEDURE' to 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.

    The Timestamp and Grantor columns currently are unused and are discussed no further here.

    Scope columns in the grant tables contain strings. They are declared as shown here; the default value for each is the empty string.

    Column Name Type
    Host CHAR(60)
    User CHAR(16)
    Password CHAR(41)
    Db CHAR(64)
    Table_name CHAR(64)
    Column_name CHAR(64)
    Routine_name CHAR(64)

    For access-checking purposes, comparisons of User, Password, Db, and Table_name values are case sensitive. Comparisons of Host, Column_name, and Routine_name values are not case sensitive.

    In the user, db, and host tables, each privilege is listed in a separate column that is declared as ENUM('N','Y') DEFAULT 'N'. In other words, each privilege can be disabled or enabled, with the default being disabled.

    In the tables_priv, columns_priv, and procs_priv tables, the privilege columns are declared 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 enabled.

    Table Name Column Name Possible Set Elements
    tables_priv Table_priv 'Select', 'Insert', 'Update', 'Delete', 'Create', 'Drop', 'Grant', 'References', 'Index', 'Alter', 'Create View', 'Show view', 'Trigger'
    tables_priv Column_priv 'Select', 'Insert', 'Update', 'References'
    columns_priv Column_priv 'Select', 'Insert', 'Update', 'References'
    procs_priv Proc_priv 'Execute', 'Alter Routine', 'Grant'

    Administrative privileges (such as RELOAD or SHUTDOWN) are specified only in the user table. 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, to determine whether you can perform an administrative operation, the server need consult only the user table.

    The FILE privilege also is specified only in the user table. It is not an administrative privilege as such, but your ability to read or write files on the server host is independent of the database you are accessing.

    The mysqld 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 5.4.6, “When Privilege Changes Take Effect”.

    When you modify an account's privileges, it is a good idea to verify that the changes set up privileges the way you want. To check the privileges for a given account, use the SHOW GRANTS statement (see Section 12.4.5.22, “SHOW GRANTS Syntax”). For example, to determine the privileges that are granted to an account with user name and host name values of bob and pc84.example.com, use this statement: 

    SHOW GRANTS FOR 'bob'@'pc84.example.com';