e.g. shrink table usage

Steps:
SQL>
exec dbms_stats.gather_table_stats('HR','EMPLOYEES');
-- Gathering table statistics

SQL>
SELECT owner,
       table_name,
       ROUND ( (num_rows * avg_row_len) / (1024 * 1024)) MB
  FROM dba_tables
 WHERE table_name = 'EMPLOYEES';
-- Check table actual size

SQL>
  SELECT table_name,
         ROUND ( (blocks * 8) / 1024, 2) "size (MB)",
         ROUND ( (num_rows * avg_row_len / 1024 / 1024), 2) "actual_data (MB)",
         (  ROUND ( (blocks * 8) / 1024, 2)
          - ROUND ( (num_rows * avg_row_len / 1024 / 1024), 2))
            "wasted_space (MB)"
    FROM dba_tables
   WHERE     (ROUND ( (blocks * 8), 2) >
                 ROUND ( (num_rows * avg_row_len / 1024), 2))
         AND table_name = 'EMPLOYEES'
         AND OWNER LIKE 'HR'
ORDER BY 4 DESC;
-- Check table current, actual, wasted size

SQL>
ALTER TABLE HR.EMPLOYEES ENABLE ROW MOVEMENT;
-- Enable feature before the operation

SQL>
ALTER TABLE HR.EMPLOYEES SHRINK SPACE COMPACT;
-- Online operation without HWM (High Water Mark) fix

SQL>
ALTER TABLE HR.EMPLOYEES SHRINK SPACE;
-- Table will be locked for any DML commands 

SQL>
ALTER TABLE HR.EMPLOYEES DISABLE ROW MOVEMENT;
-- Disable feature after the operation

SQL>
  SELECT table_name,
         ROUND ( (blocks * 8) / 1024, 2) "size (MB)",
         ROUND ( (num_rows * avg_row_len / 1024 / 1024), 2) "actual_data (MB)",
         (  ROUND ( (blocks * 8) / 1024, 2)
          - ROUND ( (num_rows * avg_row_len / 1024 / 1024), 2))
            "wasted_space (MB)"
    FROM dba_tables
   WHERE     (ROUND ( (blocks * 8), 2) >
                 ROUND ( (num_rows * avg_row_len / 1024), 2))
         AND table_name = 'EMPLOYEES'
         AND OWNER LIKE 'HR'
ORDER BY 4 DESC;
-- Lastly, Check table current, actual, wasted size again

Ref: http://select-star-from.blogspot.com.tr/2013/09/how-to-check-table-fragmentation-in.html

DBMS_JOBS vs DBMS_SCHEDULER

-> DBMS_SCHEDULER introduced in 10g releases so before this, we were able to use only DBMS_JOBS for scheduler jobs.

e.g. DBMS_JOBS
SQL>
VARIABLE job_id NUMBER;
BEGIN
  DBMS_JOB.submit (
    job       => :job_id,
    what      => 'BEGIN P_KILL_ALL_INACTIVE_SESSIONS; END;',
    next_date => SYSDATE,
    interval  => 'SYSDATE + 1 /* 1 Day */');
  COMMIT;
END;
/
PRINT job_id

e.g. DBMS_SCHEDULER
SQL>
BEGIN
  DBMS_SCHEDULER.create_job (
    job_name        => 'example_job',
    job_type        => 'PLSQL_BLOCK',
    job_action      => 'BEGIN P_KILL_ALL_INACTIVE_SESSIONS; END;',
    start_date      => SYSTIMESTAMP,
    repeat_interval => 'SYSTIMESTAMP + 1 /* 1 Day */');
END;
/

Ref for example: https://ozsoyler.blogspot.com.tr/2017/02/how-to-kill-all-inactive-sessions-with.html

How to monitor TEMP tablespace resource usage?

-> Check Total TEMP usage:
SQL>
SELECT B.TOTAL_MB,
       B.TOTAL_MB - ROUND (A.USED_BLOCKS * 8 / 1024) CURRENT_FREE_MB,
       ROUND (USED_BLOCKS * 8 / 1024) CURRENT_USED_MB,
       ROUND (MAX_USED_BLOCKS * 8 / 1024) MAX_USED_MB
  FROM V$SORT_SEGMENT A,
       (SELECT ROUND (SUM (BYTES) / 1024 / 1024) TOTAL_MB FROM DBA_TEMP_FILES) B;

-> Check Total TEMP usage according to database blocks:
SQL>
SELECT DISTINCT S.SID,
                  S.USERNAME,
                  U.TABLESPACE,
                  S.SQL_HASH_VALUE || '/' || U.SQLHASH HASH_VALUE,
                  U.SEGTYPE,
                  U.CONTENTS,
                  U.BLOCKS
    FROM V$SESSION S, V$TEMPSEG_USAGE U
   WHERE S.SADDR = U.SESSION_ADDR
ORDER BY U.BLOCKS DESC;

-> Find problematic SQL for TEMP
SQL>
SELECT 
      S.SID
     ,S.CLIENT_INFO
     ,S.MACHINE
     ,S.PROGRAM
     ,S.TYPE
     ,S.LOGON_TIME
     ,S.OSUSER
     ,SQ.SORTS
     ,SQ.DISK_READS
     ,SQ.BUFFER_GETS
     ,SQ.ROWS_PROCESSED
     ,SQ.SQLTYPE
     ,SQ.SQL_TEXT
 FROM GV$SESSION S    
    , GV$SQL SQ
WHERE S.SQL_HASH_VALUE = SQ.HASH_VALUE
  --AND s.inst_id= 1
  AND S.SID = 555 
  AND SQ.INST_ID= S.INST_ID;

e.g. simple DDL audit trigger

e.g. DDL audit trigger

CREATE TABLE SYSTEM.audit_ddl_history
(
osuser varchar2(50),
session_user varchar2(50),
host varchar2(50),
terminal varchar2(50),
object_owner varchar2(50),
obejct_type varchar2(50),
object_name varchar2(50),
sysevent varchar2(50),
audit_date date
);

CREATE OR REPLACE TRIGGER SYSTEM.ALPERDB_AUDIT_HISTORY
   AFTER DDL
   ON DATABASE
begin
if (ora_sysevent='GRANT')
  then
  NULL; -- don't care to grant!
  else
    insert into SYSTEM.audit_ddl_history(osuser, session_user, host, terminal, object_owner, obejct_type, object_name, sysevent,audit_date)
    values(
      sys_context('USERENV','OS_USER') ,
      sys_context('USERENV','SESSION_USER') , 
      sys_context('USERENV','HOST') , 
      sys_context('USERENV','TERMINAL') ,
      ora_dict_obj_owner,
      ora_dict_obj_type,
      ora_dict_obj_name,
      ora_sysevent,
    sysdate
    );
  end if;
end;
/

e.g.
SQL>
SELECT SYS_CONTEXT ('USERENV', 'SESSION_USER') FROM DUAL;

Ref: https://docs.oracle.com/cd/B10501_01/appdev.920/a96590/adg14evt.htm

Solution ORA-01031, ORA-01994

Error
ORA-01031: insufficient privileges

Solution
Give sysdba role to sys
SQL> grant sysdba to sys; 

If you get this error ->
ORA-01994: GRANT failed: password file missing or disabled

Run following command;
$ orapwd file=$ORACLE_HOME/dbs/orapw$ORACLE_SID password=alper entries=2 force=y
-> entries; number of users can login as sysdba role
-> force; enable to overwrite current pwd file

Check remote_login parameter
SQL> show parameter remote_login_passwordfile;

If remote_login_passwordfile is not "EXCLUSIVE";
Change it permanently:
add this into init.ora file;
*.remote_login_passwordfile='EXCLUSIVE'

Check who has sysdba role in database lastly
SQL> select * from V$PWFILE_USERS;

How to start/stop/configure samba service?

If you need, uninstall old samba
# yum erase samba samba-common samba-client 

install tool
# yum install samba4

or upgrade tool
# yum upgrade samba4

configure settings
# vi /etc/samba/smb.conf

e.g.
[share_folder]
 comment = Share Folder
 path = /share_folder
 create mode = 0777
 readonly = no
 browseable = yes
 public = yes

Check configuration of samba
# testparm

check samba service and version
# smbstatus

startup options
# chkconfig smb on
# service smb start

connect to share folder
e.g. 
RUN> \\10.10.10.10\share_folder

remove startup option and stop vnc
# chkconfig smb off
# service smb stop

ORA-28002 solution

Error
ORA-28002: the password will expire within [A] days

Solution
Disable password expiration
SQL> select profile from DBA_USERS where username = 'HR';
-- e.g. DEFAULT

Change password_life_time parameter
SQL> alter profile "DEFAULT" limit password_life_time UNLIMITED;

Check it
SQL> select resource_name,limit from dba_profiles where profile='DEFAULT';

Apply the new setting for user
SQL> alter user "HR" identified by "hr";