5.7. Privileges
When an object is created, it is assigned an owner. The owner is normally the role that executed the creation statement. For most kinds of objects, the initial state is that only the owner (or a superuser) can do anything with the object. To allow other roles to use it, privileges must be granted.
There are different kinds of privileges:
SELECT
,
INSERT
,
UPDATE
,
DELETE
,
TRUNCATE
,
REFERENCES
,
TRIGGER
,
CREATE
,
CONNECT
,
TEMPORARY
,
EXECUTE
,
USAGE
,
SET
and
ALTER SYSTEM
.
The privileges applicable to a particular
object vary depending on the object's type (table, function, etc.).
More detail about the meanings of these privileges appears below.
The following sections and chapters will also show you how
these privileges are used.
The right to modify or destroy an object is inherent in being the object's owner, and cannot be granted or revoked in itself. (However, like all privileges, that right can be inherited by members of the owning role; see Section 22.3 .)
An object can be assigned to a new owner with an
ALTER
command of the appropriate kind for the object, for example
ALTER TABLEtable_name
OWNER TOnew_owner
;
Superusers can always do this; ordinary roles can only do it if they are
both the current owner of the object (or inherit the privileges of the
owning role) and able to
SET ROLE
to the new owning role.
To assign privileges, the
GRANT
command is
used. For example, if
joe
is an existing role, and
accounts
is an existing table, the privilege to
update the table can be granted with:
GRANT UPDATE ON accounts TO joe;
Writing
ALL
in place of a specific privilege grants all
privileges that are relevant for the object type.
The special
"
role
"
name
PUBLIC
can
be used to grant a privilege to every role on the system. Also,
"
group
"
roles can be set up to help manage privileges when
there are many users of a database - for details see
Chapter 22
.
To revoke a previously-granted privilege, use the fittingly named REVOKE command:
REVOKE ALL ON accounts FROM PUBLIC;
Ordinarily, only the object's owner (or a superuser) can grant or revoke privileges on an object. However, it is possible to grant a privilege " with grant option " , which gives the recipient the right to grant it in turn to others. If the grant option is subsequently revoked then all who received the privilege from that recipient (directly or through a chain of grants) will lose the privilege. For details see the GRANT and REVOKE reference pages.
An object's owner can choose to revoke their own ordinary privileges, for example to make a table read-only for themselves as well as others. But owners are always treated as holding all grant options, so they can always re-grant their own privileges.
The available privileges are:
-
SELECT
# -
Allows
SELECT
from any column, or specific column(s), of a table, view, materialized view, or other table-like object. Also allows use ofCOPY TO
. This privilege is also needed to reference existing column values inUPDATE
,DELETE
, orMERGE
. For sequences, this privilege also allows use of thecurrval
function. For large objects, this privilege allows the object to be read. -
INSERT
# -
Allows
INSERT
of a new row into a table, view, etc. Can be granted on specific column(s), in which case only those columns may be assigned to in theINSERT
command (other columns will therefore receive default values). Also allows use ofCOPY FROM
. -
UPDATE
# -
Allows
UPDATE
of any column, or specific column(s), of a table, view, etc. (In practice, any nontrivialUPDATE
command will requireSELECT
privilege as well, since it must reference table columns to determine which rows to update, and/or to compute new values for columns.)SELECT ... FOR UPDATE
andSELECT ... FOR SHARE
also require this privilege on at least one column, in addition to theSELECT
privilege. For sequences, this privilege allows use of thenextval
andsetval
functions. For large objects, this privilege allows writing or truncating the object. -
DELETE
# -
Allows
DELETE
of a row from a table, view, etc. (In practice, any nontrivialDELETE
command will requireSELECT
privilege as well, since it must reference table columns to determine which rows to delete.) -
TRUNCATE
# -
Allows
TRUNCATE
on a table. -
REFERENCES
# -
Allows creation of a foreign key constraint referencing a table, or specific column(s) of a table.
-
TRIGGER
# -
Allows creation of a trigger on a table, view, etc.
-
CREATE
# -
For databases, allows new schemas and publications to be created within the database, and allows trusted extensions to be installed within the database.
For schemas, allows new objects to be created within the schema. To rename an existing object, you must own the object and have this privilege for the containing schema.
For tablespaces, allows tables, indexes, and temporary files to be created within the tablespace, and allows databases to be created that have the tablespace as their default tablespace.
Note that revoking this privilege will not alter the existence or location of existing objects.
-
CONNECT
# -
Allows the grantee to connect to the database. This privilege is checked at connection startup (in addition to checking any restrictions imposed by
pg_hba.conf
). -
TEMPORARY
# -
Allows temporary tables to be created while using the database.
-
EXECUTE
# -
Allows calling a function or procedure, including use of any operators that are implemented on top of the function. This is the only type of privilege that is applicable to functions and procedures.
-
USAGE
# -
For procedural languages, allows use of the language for the creation of functions in that language. This is the only type of privilege that is applicable to procedural languages.
For schemas, allows access to objects contained in the schema (assuming that the objects' own privilege requirements are also met). Essentially this allows the grantee to " look up " objects within the schema. Without this permission, it is still possible to see the object names, e.g., by querying system catalogs. Also, after revoking this permission, existing sessions might have statements that have previously performed this lookup, so this is not a completely secure way to prevent object access.
For sequences, allows use of the
currval
andnextval
functions.For types and domains, allows use of the type or domain in the creation of tables, functions, and other schema objects. (Note that this privilege does not control all " usage " of the type, such as values of the type appearing in queries. It only prevents objects from being created that depend on the type. The main purpose of this privilege is controlling which users can create dependencies on a type, which could prevent the owner from changing the type later.)
For foreign-data wrappers, allows creation of new servers using the foreign-data wrapper.
For foreign servers, allows creation of foreign tables using the server. Grantees may also create, alter, or drop their own user mappings associated with that server.
-
SET
# -
Allows a server configuration parameter to be set to a new value within the current session. (While this privilege can be granted on any parameter, it is meaningless except for parameters that would normally require superuser privilege to set.)
-
ALTER SYSTEM
# -
Allows a server configuration parameter to be configured to a new value using the ALTER SYSTEM command.
The privileges required by other commands are listed on the reference page of the respective command.
PostgreSQL grants privileges on some types of objects to
PUBLIC
by default when the objects are created.
No privileges are granted to
PUBLIC
by default on
tables,
table columns,
sequences,
foreign data wrappers,
foreign servers,
large objects,
schemas,
tablespaces,
or configuration parameters.
For other types of objects, the default privileges
granted to
PUBLIC
are as follows:
CONNECT
and
TEMPORARY
(create
temporary tables) privileges for databases;
EXECUTE
privilege for functions and procedures; and
USAGE
privilege for languages and data types
(including domains).
The object owner can, of course,
REVOKE
both default and expressly granted privileges. (For maximum
security, issue the
REVOKE
in the same transaction that
creates the object; then there is no window in which another user
can use the object.)
Also, these default privilege settings can be overridden using the
ALTER DEFAULT PRIVILEGES
command.
Table 5.1 shows the one-letter abbreviations that are used for these privilege types in ACL (Access Control List) values. You will see these letters in the output of the psql commands listed below, or when looking at ACL columns of system catalogs.
Table 5.1. ACL Privilege Abbreviations
Privilege | Abbreviation | Applicable Object Types |
---|---|---|
SELECT
|
r
(
"
read
"
)
|
LARGE OBJECT
,
SEQUENCE
,
TABLE
(and table-like objects),
table column
|
INSERT
|
a
(
"
append
"
)
|
TABLE
, table column
|
UPDATE
|
w
(
"
write
"
)
|
LARGE OBJECT
,
SEQUENCE
,
TABLE
,
table column
|
DELETE
|
d
|
TABLE
|
TRUNCATE
|
D
|
TABLE
|
REFERENCES
|
x
|
TABLE
, table column
|
TRIGGER
|
t
|
TABLE
|
CREATE
|
C
|
DATABASE
,
SCHEMA
,
TABLESPACE
|
CONNECT
|
c
|
DATABASE
|
TEMPORARY
|
T
|
DATABASE
|
EXECUTE
|
X
|
FUNCTION
,
PROCEDURE
|
USAGE
|
U
|
DOMAIN
,
FOREIGN DATA WRAPPER
,
FOREIGN SERVER
,
LANGUAGE
,
SCHEMA
,
SEQUENCE
,
TYPE
|
SET
|
s
|
PARAMETER
|
ALTER SYSTEM
|
A
|
PARAMETER
|
Table 5.2 summarizes the privileges available for each type of SQL object, using the abbreviations shown above. It also shows the psql command that can be used to examine privilege settings for each object type.
Table 5.2. Summary of Access Privileges
Object Type | All Privileges |
Default
PUBLIC
Privileges
|
psql Command |
---|---|---|---|
DATABASE
|
CTc
|
Tc
|
\l
|
DOMAIN
|
U
|
U
|
\dD+
|
FUNCTION
or
PROCEDURE
|
X
|
X
|
\df+
|
FOREIGN DATA WRAPPER
|
U
|
none |
\dew+
|
FOREIGN SERVER
|
U
|
none |
\des+
|
LANGUAGE
|
U
|
U
|
\dL+
|
LARGE OBJECT
|
rw
|
none |
\dl+
|
PARAMETER
|
sA
|
none |
\dconfig+
|
SCHEMA
|
UC
|
none |
\dn+
|
SEQUENCE
|
rwU
|
none |
\dp
|
TABLE
(and table-like objects)
|
arwdDxt
|
none |
\dp
|
Table column |
arwx
|
none |
\dp
|
TABLESPACE
|
C
|
none |
\db+
|
TYPE
|
U
|
U
|
\dT+
|
The privileges that have been granted for a particular object are
displayed as a list of
aclitem
entries, each having the
format:
grantee
=
privilege-abbreviation
[*
].../
grantor
Each
aclitem
lists all the permissions of one grantee that
have been granted by a particular grantor. Specific privileges are
represented by one-letter abbreviations from
Table 5.1
, with
*
appended if the privilege was granted with grant option. For example,
calvin=r*w/hobbes
specifies that the role
calvin
has the privilege
SELECT
(
r
) with grant option
(
*
) as well as the non-grantable
privilege
UPDATE
(
w
), both granted
by the role
hobbes
. If
calvin
also has some privileges on the same object granted by a different
grantor, those would appear as a separate
aclitem
entry.
An empty grantee field in an
aclitem
stands
for
PUBLIC
.
As an example, suppose that user
miriam
creates
table
mytable
and does:
GRANT SELECT ON mytable TO PUBLIC; GRANT SELECT, UPDATE, INSERT ON mytable TO admin; GRANT SELECT (col1), UPDATE (col1) ON mytable TO miriam_rw;
Then
psql
's
\dp
command
would show:
=> \dp mytable Access privileges Schema | Name | Type | Access privileges | Column privileges | Policies --------+---------+-------+-----------------------+-----------------------+---------- public | mytable | table | miriam=arwdDxt/miriam+| col1: +| | | | =r/miriam +| miriam_rw=rw/miriam | | | | admin=arw/miriam | | (1 row)
If the
"
Access privileges
"
column is empty for a given
object, it means the object has default privileges (that is, its
privileges entry in the relevant system catalog is null). Default
privileges always include all privileges for the owner, and can include
some privileges for
PUBLIC
depending on the object
type, as explained above. The first
GRANT
or
REVOKE
on an object will instantiate the default
privileges (producing, for
example,
miriam=arwdDxt/miriam
) and then modify them
per the specified request. Similarly, entries are shown in
"
Column
privileges
"
only for columns with nondefault privileges.
(Note: for this purpose,
"
default privileges
"
always means
the built-in default privileges for the object's type. An object whose
privileges have been affected by an
ALTER DEFAULT
PRIVILEGES
command will always be shown with an explicit
privilege entry that includes the effects of
the
ALTER
.)
Notice that the owner's implicit grant options are not marked in the
access privileges display. A
*
will appear only when
grant options have been explicitly granted to someone.