Ok, you are a newcomer SAP BASIS administrator, but you didn’t get any passwords from the previous SAP guy. Your target is to get access to SAP* in a certain client, but you only have access to the application and database server’s OS. The algorithm of overtaking is:
OS > SYSTEM@SYSTEMDB >SYSTEM@TENANTDB > SAPHANADB@TENANTDB > SAP*

1. Taking over SYSTEM user of HANA SYSTEM DB:
   su – <hanadb user>
   HDB stop
hdbenv.sh
hdbnameserver -resetUserSystem
sapcontrol -nr $TINSTANCE -function StartSystem HDB
   
2. Taking over SYSTEM user of HANA TENANT DB:
   As SYSTEM@SYSTEMDB:
   ALTER SYSTEM STOP DATABASE <TENANTDB>
ALTER DATABASE <TENANTDB> SYSTEM USER PASSWORD "MY_NEW_PASSWORD";
ALTER SYSTEM START DATABASE <TENANTDB>
   
3. Taking over SAPHANADB user in HANA TENANT DB:
   As SYSTEM@TENANTDB:
   ALTER USER SAPHANADB password "MY_NEW_PASSWORD" NO FORCE_FIRST_PASSWORD_CHANGE;
   
   Changing the password in hdbuserstore of application server:
   su – <application server user>
   hdbuserstore -i SET DEFAULT <sap-hanadb-hostname>:3<instance>13@<TENANTDB> SAPHANADB
   
   Unlock and reset connect attempts count:
   As SYSTEM@TENANTDB:
   ALTER USER SAPHANADB1 RESET CONNECT ATTEMPTS;
ALTER USER SAPHANADB1 ACTIVATE USER NOW;
   
   Checking:
   su – <application server user>
   hdbsql -U DEFAULT
   
   SQL>
   SELECT * FROM T000;
   
   
   
4. Taking over SAP* in the client:
   su – <application server user>
   Check for the parameter login/no_automatic_user_sapstar = 0 in the SAP application server’s profiles.
   
   As SAPHANADB@TENANTDB:
   Check and remove the created SAP* user to remove its override:
   select * from USR02 where MANDT = <MANDT> and BNAME=’SAP*’;
   delete from USR02 where MANDT = <MANDT> and BNAME=’SAP*’;
   
   Login with SAP* user and default password “pass”.
   Do not forget to bring it all back!