Hi,
I have solved the problem. I did the following:
I have corrupted /
myinstance/sqllib/cfg/IBMLDAPSecurity.ini file which is Tivoli client file. I have commented lines where LDAP group is specified in ini file and DB2 was returning errors but let me be an instance owner again.
Then I have set dbm cfg GROUP_PLUGIN to NULL thanks to
Stolze tip.
Then I have set dbm cfg SRVCON_PW_PLUGIN to NULL.
And db2set to DB2_ENABLE_LDAP=NO
Then I have restarted the instance and now Linux is authenticating users again.
Now first of all I have to make a backup of database...
Regards,
Grofaty