Category Archives: Unix/Linux

Can’t su to oracle user

Last week, got this issue reported by a DBA that he wasn’t able to su to oracle user from root on a Oracle Base Database VM in OCI. The login of opc user worked fine and he could do sudo su to root but he couldn’t su to oracle. When he did it just came back to root shell.

[root@xxx ~]# su - oracle
Last login: Fri Jan 12 10:20:38 UTC 2023
[root@xxx ~]#

There was nothing relevant in /var/log/messages or /var/log/secure. I tried it for some other user and it worked fine. Then I suspected something with the profile of oracle user and voila ! The .bashrc looked like this

[root@xxx oracle]# pwd
/home/oracle
[root@xxx oracle]# more .bashrc
exit
[root@xxx oracle]#

So the moment it logged in with user oracle, there was an exit command in .bashrc and it used to exit. Problem solved. I don’t know who did it but it looks like a mischief done by someone.

Smokescreen detects traffic from an Exadata VM

A customer who is using an Exadata X8M-2 with multiple VMs had Smokescreen deployed in their company recently and they reported an issue that one of the Smokescreen decoy servers in their DC was seeing traffic from one of the Exadata VMs on a certain port. That was rather confusing as that port was the database listener port on that VM and why would a VM with Oracle RAC deployed try to access any random IP on the listener port. Also it was happening only for this VM. Nothing for so many other VMs.

We were just looking at the things and my colleague said that he had seen this IP somewhere and he started looking through the emails. In a minute, we found the issue as he found this IP mentioned in one of the emails. This was the VIP of this VM from where the traffic was reported to be originating. While reserving IPs for Smokescreen decoy servers, someone made the mess and re-used the IP that was already used for one of the VIPs of this RAC system !

TNS-12543: TNS:destination host unreachable

Scenario : Setting up a physical standby from Exadata to a non-Exadata single instance. tnsping from standby to primary works fine but tnsping from primary to standby fails with:

TNS-12543: TNS:destination host unreachable

I am able to ssh standby from primary, can ping as well but tnsping doesn’t work. ¬†From the error description we can figure out that something is blocking the access. In this case it was iptables that was enabled on the standby server.

Stopping the service resolved the issue.

service iptables stop
chkconfig iptables off

The error is an obvious one but sometimes it just doesn’t strike you that it could be something simple like that.

Manually booting an OS from GRUB

One of my friend today asked me about removing Linux partitions & GRUB (from a dual boot system) and return back to windows alone. Removing Linux involves just formatting/removing the partitions. Now to remove GRUB either do fdisk /mbr from a Windows 98 bootable CD or do fixmbr after booting into repair mode with Windows XP CD. But if you have none then to remove GRUB you will need some utility like this one and if you reboot before doing that it might make GRUB unable to boot into Windows. It will get stuck at GRUB> prompt only. So there is an option: to manually boot the OS you want (ie Windows). A quick search gave link to this thread. It involves few commands on the GRUB prompt:

grub> rootnoverify (hd0,0)
grub> makeactive
grub> chainloader +1
grub> boot

It will load the NTLDR where your Windows is installed in Partition 1 on HDD 1.

Unxutils for Windows

If you are used to work in Unix enviroment and then sometime, in between have to sit on Windows and tail -f alert_DB.log, its a real pain. There is a small bundle of utilities, called Unxutils which can make you feel at home in Windows too. These are the exe’s of all major commands in Unix like more, less, ls, grep etc…
To use it just download the zip file from the link above, extract it to some folder and add the path of exe’s to your Windows PATH. Restart your machine and you are done.
Happy more’ing…less’ing…