How to restore root access on a KVM guest running Oracle Linux 7 on Exadata (X8M)

A few days ago, I made a handling error on an Oracle Linux 7 virtual machine on a freshly configured Exadata X8M. I inadvertently renamed the files “/etc/pam.d/password-auth” and “/etc/pam.d/system-auth”. Result: I was no longer able to connect to the VM in ssh, or even via the virsh console.

I will describe here the steps to regain access by renaming the files with the right name, but it is also applicable if you have lost your root password.

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Simulate a where clause on a “long” type column from SQLPlus

As a DBA you sometimes have to take time to look for tricks to accomplish tasks that seem simple at first glance. A few days ago, I was asked to identify tables that had sequences prefixed by the schema name as a default value in the columns. You may think: it’s an easy task, just filter on the “data_default” column of the “dba_tab_columns” view, but unfortunately it’s not that simple using SQLPlus. The “data_default” column is in “longdatatype, so you cannot include it directly in the “where” clause of a query.

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Retrieve serial numbers and other useful information from Exadata

It’s been a while since my last post!
Today, I wanted to share with you some useful commands to extract information from Exadata (product name, serial numbers, …).
This can be helpful for the opening of an new SR for example, or for inventorying components in a CMDB.

Here is the list of interesting elements that can be extracted (the list is not exhaustive, but these are the ones I use most often):

Exadata product name
Exadata rack serial number
Compute nodes and cell nodes serial number
Compute nodes and cell nodes internal component’s serial number
Inifiniband switches serial number
Cisco switch serial number
PDU’s serial number

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How user authentication works in a shared MongoDB cluster

Today, I want to clarify an important point about users authentication in a MongoDB sharded cluster because this seems to be misunderstood by some people.

In a such environment, there are two notions to understand about user authentication, especially when you are DBA:

  • cluster¬†authentication, that is, the authentication made when connected trough a “mongos” process.
  • local¬†authentication, that is, the authentication made when connected locally on a shard trough a “mongod” process.

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Install EM13c agent and add targets using the Linux command line only

A few days ago, I was asked to find a way to automate the addition of newly created Linux virtual machines and databases in our EM13c console. Of course, no action should be performed via the EM web interface!

For the first part (installing the EM13c agent on newly created virtual machines), it’s quite simple, because Oracle gives you many methods (for example, “agent pull” method), in order to carry out this task. But the second part seemed more delicate according to the documentation and my constraints: everything must be done on the virtual machine. I am not allowed to connect to the EM server using SSH.

Fortunately, there is a simple solution that only requires a few extra lines in your shell script!

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Elasticsearch: useful commands for DBAs

As a production DBA, you can fall into a situation where you have to act on an environment you do not know.

It can be very difficult to understand how the architecture was designed, but if you know the right commands, you can get a quick overview and all the information you need to start working.

Today, I’m going to give you these basic commands that will help you understand how an Elasticsearch installation was performed on an RHEL system.

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Retrieve the exit code of all the commands in a pipeline with “PIPESTATUS”

When developing shell scripts, it is common usage to check the exit code of a command in order to check if its execution was successful or not. It is pretty easy when you execute only one command, because the exit code can be find using the special parameter “$?”. But if you use pipelines (“command1 | command2 | …”), it is not that simple because “$?” will only give you the exit code of the last command of your pipeline.

So, today, I’m going to show you how to get the exit code for each command in a pipeline. Unfortunately, this only works in bash.

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