Category: Sys Admin

Nagios Monitoring of Directories

I had a recent occurrence at work that caused me to look around for a tool to monitor a directory for any changes made. Since there didn’t seem to be anything out there, I created a check called dirchanged. It looks at all the files in a directory and creates an sha256 has of the names and contents of the files. That hash is compared to a known value to determine if there have been any changes made.

There are a couple of issues with this check specifically that it doesn’t look into subdirectories and that the hash for comparison is passed on the command line from within the Nagios configuration files. I think the first issue will be fixed soon enough w/ a flag to indicate if the directory tree is to be traversed. The second issue is more cumbersome in that the hash value has to be stored somewhere. I’m not yet certain that putting it in the Nagios configuration files is better than putting it somewhere on the target file system. From the security standpoint, having the check not stored on the target file system is better, much less chance of it being changed by bad guys.

I’ll let it run for a while and see how it behaves and if changes are warranted.

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Customer Service

It seems that there is still some good customer service out there. This conversation took place after a few second wait and lasted around 1 minute.

Thank you for choosing Adobe. A representative will be with you shortly. Your estimated wait time is 0 minute(s) and 3 second(s) or longer as there are 1 customer(s) in line ahead of you.

You are now chatting with Abhinandan.

Abhinandan: Thank you for contacting Adobe chat support, my name is Abhinandan, I have received your query. Please allow me a moment to review the details of your request.

Abhinandan: Hello Peter, how are you?

peter: doing ok

Abhinandan: Thank you.

Abhinandan: May I please have your email address registered with Adobe?


Abhinandan: Thank you.

Abhinandan: Could you please provide me the serial number of your product?

peter: nnnn nnnn nnnn nnnn nnnn nnnn

Abhinandan: Thank you.

Abhinandan: May I know what exact error you are facing?

peter: my laptop was stolen. i’ve purchased a replacement laptop, restored from my backups and i’m now trying to use illustrator. when launching, it asks to be activated. when i try to activate, i receive “activation limit reached for adobe creative suite 5 web premium.”

Abhinandan: I will solve this issue for you.

peter: excellent

Abhinandan: You are welcome.

Abhinandan: I have made necessary changes from my end, request you to please try reactivating your product.

Abhinandan: Please close and re launch the product.

Abhinandan: Is it working?

peter: problem solved! you have my thanks.

Abhinandan: Great!

Abhinandan: Is there anything else I can help you with?

peter: that was my only issue.

Abhinandan: You may receive an email survey in reference to this interaction with Adobe. Your feedback is very much appreciated.

Abhinandan: Thank you for contacting Adobe.  We are available 7 days a week, 24 hours a day. Goodbye!

Thank you for chatting with us. Please click the “Close” button on the top right of the chat window to tell us how we did today.

Thanks Abhinandan and thanks Adobe!

Erasing a Hard Disk

I recently had the need to recycle several old computers and by old, I mean Power Mac G4 old. These systems were state of the art in 1999.

As any good IT professional knows, you don’t want to just recycle any computers without first erasing the data on the hard disks. Now I doubt that there’s anything of any importance on the disks but it’s better to erase them to be certain. A traditional way would be to reinitialize the disk and overwrite all the sectors several times. But why follow tradition when there are so many other, more creative ways to erase the contents!

I think I’ve come up with a method guaranteed to destroy the contents of a hard disk for those occasions when you need to be reasonably sure that the data can never be recovered.

What do you think? Too much?

Now before you think of trying this at home let me just say no, stop, don’t try this at home. That’s insane. This forge was running at approximately 2,300 degrees fahrenheit. There’s no way any appliance in your house generates nearly enough heat to reproduce this madness. Just put the thought out of your head.

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SSH and OS X

This has been driving me nuts for the past several months but I hadn’t made the time to figure out the problem. Basically, the only account that could be used to ssh into our OS X server was the admin account. The admin account lives in the traditional Unix /etc/passwd database. Any account that was created via Workgroup Manager, like mine, (that is one that lives in Open Directory, OS X’s LDAP authentication database) wouldn’t work. As I said, this has been driving me nuts and I finally spent some time digging through the man pages, configuration files and log files to figure out what was going on.

It seems that a previous sysadmin had added the AllowUsers keywords to the sshd configuration file in /etc/sshd_config. On the AllowUsers line were listed the users who were able to connect via ssh. And wouldn’t you know, my account wasn’t listed.

I got to this point by reading through the /var/log/secure.log file to see what OS X was recording as the problem with connecting. There was one line in particular that stood out:

Jan 18 15:13:09 xyzzy sshd[4656]: User peter from not allowed because not listed in AllowUsers

AllowUsers? That’s strange. I don’t remember anywhere in OS X that would use a convention like this to control the environment. But a quick search on Google shows that this was a keyword used in the sshd configuration file. Adding my account name to the list and I was able to ssh in without any problem. Oh yeah, life is good!

One cool side note, sshd didn’t have to be restarted. It’s smart enough to know the configuration file has changed. Makes it very easy to test configuration changes.

But modifying the /etc/sshd_config file every time I need to allow ssh access to someone isn’t an easy way to manage account priveleges on OS X. Looking a bit more at the sshd_config man page shows that there’s also a AllowGroup option. So I removed the AllowUsers line and replaced it with:

AllowGroup ssh

Then using the standard Workgroup Manager, I added a new group called ssh and put the various accounts that need ssh access into the group. Now any accounts that needs ssh access can easily be added (or removed) from the ssh group and sshd will automatically give them access.


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