Search notes:

ORA-65096: invalid common user or role name

$ sqlplus / as sysdba

SQL> create user tq84_ora_65096_demo identified by aWeakPassword;
--
-- ORA-65096: invalid common user or role name
--

Check to which container we're connected:

SQL> select
   ses.con_id,
   case when con.con_id = ses.con_id then 'X' end cur_con, -- current container
   con.name
from
   v$session    ses   cross join
   v$containers con
where
   ses.sid = sys_context('userenv', 'sid') -- Identify own session
; 
--
-- CON_ID C NAME
-- ------ - ------------
--      1 X CDB$ROOT
--          PDB$SEED
--          PDBTQ84

We're connected to the root container (CDB$ROOT).

Trying again to create a user (without c## prefix) on a PDB:

SQL> connect sys/elCarosSecret4@pdbtq84 as sysdba

SQL> select
   ses.con_id,
   case when con.con_id = ses.con_id then 'X' end cur_con, -- current container
   con.name
from
   v$session    ses   cross join
   v$containers con
where
   ses.sid = sys_context('userenv', 'sid');
--
-- CON_ID C NAME
-- ------ - ----------------
--      3 X PDBTQ84

We're on a PDB (which is the only visible container now) and ii's now possible to create the user:

SQL> create user tq84_ora_65096_demo identified by aWeakPassword;
--
-- User created.

Fatal error: Uncaught PDOException: SQLSTATE[HY000]: General error: 8 attempt to write a readonly database in /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php:78 Stack trace: #0 /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php(78): PDOStatement->execute(Array) #1 /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php(30): insert_webrequest_('/notes/developm...', 1759474050, '216.73.216.42', 'Mozilla/5.0 App...', NULL) #2 /home/httpd/vhosts/renenyffenegger.ch/httpsdocs/notes/development/databases/Oracle/errors/ORA-65096_invalid-common-user-or-role-name(86): insert_webrequest() #3 {main} thrown in /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php on line 78

ORA-65096: invalid common user or role name

See also