How to open the PDB$SEED database for patching in read/write mode

The following should only be done if you need to patch the PDB$SEED using datapatch, or under instructions from Oracle Support.

sqlplus / as sysdba
Connected to:

Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production
Version 19.22.0.0.0

SYS@cdb>SQL> alter session set container=PDB$SEED;

Session altered.

SYS@cdb>SQL>alter session set "_oracle_script"=TRUE;

Session altered.

SYS@cdb>SQL>alter pluggable database pdb$seed close immediate instances=all;

Pluggable database altered.

SYS@cdb>SQL>alter pluggable database pdb$seed OPEN READ WRITE;

Pluggable database altered.

SYS@cdb>SQL>select open_mode from v$database;

OPEN_MODE
--------------------
READ WRITE

SYS@cdb>SQL>show pdbs

    CON_ID CON_NAME                       OPEN MODE  RESTRICTED
---------- ------------------------------ ---------- ----------
         2 PDB$SEED                       READ WRITE NO
SYS@cdb>SQL>exit

To put the PDB$SEED back into READ ONLY and RESTRICTED mode:

SYS@cdb>SQL>alter pluggable database PDB$SEED close;

Pluggable database altered.

SYS@cdb>SQL>show pdbs

    CON_ID CON_NAME                       OPEN MODE  RESTRICTED
---------- ------------------------------ ---------- ----------
         2 PDB$SEED                       MOUNTED
SYS@cdb>SQL>alter pluggable database PDB$SEED open read only;

Pluggable database altered.

SYS@cdb>SQL>show pdbs

    CON_ID CON_NAME                       OPEN MODE  RESTRICTED
---------- ------------------------------ ---------- ----------
         2 PDB$SEED                       READ ONLY  NO

SYS@cdb>SQL>alter session set "_oracle_script"=FALSE;

Session altered.

SYS@cdb>SQL>show pdbs

    CON_ID CON_NAME                       OPEN MODE  RESTRICTED
---------- ------------------------------ ---------- ----------
         2 PDB$SEED                       READ ONLY  NO

SYS@cdb>SQL>alter system enable restricted session;

System altered.

SYS@cdb>SQL>show pdbs

    CON_ID CON_NAME                       OPEN MODE  RESTRICTED
---------- ------------------------------ ---------- ----------
         2 PDB$SEED                       READ ONLY  YES