Author Archives: amida168

Rocks Cluster Compute Node Installation Problem using PowerConnect N2024

We bought a PowerConnect N2024 switch for a small cluster. During the installation, the DHCP server did not seem to work. The compute node could not get an IP address and the installation failed. I saw a FAQ about the problem with PowerConnect 5224.

I had a hard time while trying to follow the guide. The first problem I had was with entering the command to assign an IP address for the switch. I didn’t know that there were two different modes for the switch. You need to enter


first to enter the command. After you enter the command, the prompt changes from > to #. You can then enter the command to assign an IP address for the switch.

interface vlan 1
ip address 255.0.0

The second problem I had was that I couldn’t find the place to change “edge port” settings. The guide suggested that this setting could be labeled as “fast link”. On the N2024 switch, it is not called either “edge port” or “fast link”; it is called Port Fast. You can enable this setting by going to Switching -> Spanning Tree -> Global Settings -> Port Fast.


Rocks Cluster Node Installation Problem “Unable to read package metadata” Solved

When I installed the first compute node in my Rocks cluster, the installation went smoothly and I didn’t have any problems. However, I ran into a lot of problems when I installed the second node.

The installation always failed with this error message:

Unable to read package metadata.This may be due to a missing repodata directory. Please ensure that your install tree has been correctly generated. Cannot retrieve repository metadata (repomd.xml) for repository: anaconda-base-201404140147.x86_64. Please verify it’s path and try again.

I searched the Rocks mailing list and found some suggestions. One suggestion was to rebuild the repository.

cd /export/rocks/install
sudo rm -rf rocks-dist
sudo rocks create distro

I did it and restarted the installation. Unfortunately, this did not fix the problem. I could not find other solutions besides rebuilding the master node.

I then began to track down the problem by myself. My clue was that the node cannot retrieve repomd.xml. I found the file under /export/rocks/install/rocks-dist/x86_64/repodata and then found the problem when I tried to list the parent directory. Here is the output:


total 20
drwxr-xr-x 5 root root 4096 Jul 29 15:41 build
drwxrwx--- 3 root root 4096 Jul 29 15:41 force
drwxr-xr-x 2 root root 4096 Jul 29 15:42 images
drwxr-xr-x 4 root root 4096 Apr 14 04:26 RedHat
drwxrwx--- 2 root root 4096 Jul 29 15:42 repodata

Note that the force and repodata directories have different permissions than others had. In order for the computer node to retrieve the repomd.xml file, the permissions have to be fixed. I changed the permissions for these two folders and restarted the installation. The installation went past the point where it failed before. However, it failed again and complained about a different file. I checked the missing file and found that there were other directories with the same permission problem. I then used this command to fix all the permission problems.

sudo chmod -R o+r,o+x /export/rocks/install


How to Enable Debug Logging on CentOS 6.5

I have been doing a lot of works on machines running CentOS 6.5 lately. The debug logging was not enabled by default. Here is how to enable it.

  1. Use a text editor to edit this file /etc/rsyslog.conf.
  2. Insert this line
    *.debug                                     /var/log/debug
  3. Save the file
  4. Restart the service by running this command
    sudo /sbin/service rsyslog restart

After the rsyslog service has been restarted, you can check this file /var/log/debug for debugging info.

“Adobe Acrobat does not support Internet Explorer’s Enhanced Protected Mode (EPM)” Error Message

One user reported that whenever she opened up a link to a PDF file from Internet Explorer, this error message popped up.



Adobe Acrobat does not support Internet Explorer’s Enhanced Protected Mode (EPM). Either install the latest version of Adobe Reader or disable EPM in Internet Explorer.

This message puzzled me for a while because Enhanced Protect Mode is for IE 10 or above. My user still uses IE 8, and there was no EPM for IE 8. I then checked the version of Acrobat Reader and it was already the latest version, so there was no need to update it.

Later, I found out that there were two Acrobats installed on the machine. One was the Acrobat Pro 9 and the other was the Acrobat Reader 11. The default program to open PDF files was set to Acrobat Pro 9 and this was the cause of the error message. I tried to set the default program to Acrobat Reader 11 and the problem was fixed.

Here are the steps to set Acrobat Reader 11 as the default program for PDF files.

  1. Open Acrobat Reader 11.
  2. Click on Edit -> Preferences.
  3. Click on General on the side bar.
  4. Click on the button Select Default PDF Handler.
  5. Click on the drop down box and select Adobe Reader XI.
  6. Click on Apply and then OK to exit out the dialogs.

adb Not Working in KitKat

After I got a LG F3 as a backup phone, I started to flash different ROMs for my HTC One X. One recent ROM I tried is KarbonKat. It’s based on CM11, which is a KitKat ROM. The ROM seems to be more stable than the official CM11 nightly that I tried earlier.

One thing I noticed is that the adb command stopped working after I flashed my phone with KarbonKat. My computer does not recognize my One X either. I tried to change the USB mode and finally got it to work.

Here is what I did:

  1. Tap on Settings.
  2. Tap on Storage.
  3. Tap on the settings icon (looks like 3 vertical dots) on the top right corner.
  4. Tap on USB computer connection.
  5. Tap on Media Device (MTP).

I then connected the phone to my computer and adb started to work again.

How to List Members in an AD Group

We need to list all the members in an AD group from time to time for review purposes. The commands are dsget and dsquery. A problem I had was that I could not remember the proper syntax for this, and every time I needed to use them, I had to look them up again. Here are the commands.

dsquery group -name "GROUP-NAME" | dsget group -members -expand

Replace the GROUP-NAME with your group name. For the first part, query the AD using the GROUP-NAME provided. Its output will be sent to dsget to list the members in the group.

Again, if you are interested in details of the commands, try the following.

dsquery /?

dsget /?

For other Windows command line tips, check out this highly recommended book: Windows Command-Line Administrator’s Pocket Consultant, 2nd Edition

Black Screen After Windows 7 Upgrade

We have been doing a lot of XP upgrades since January. One problem I encountered was with how the machine boots to a black screen after upgrading to Windows 7. There are quite a few articles on how to fix the problem. Here is a short list.

I have tried some of these suggestions, but they did not solve my problem. In the end, I replaced the video card, and I was able to get the machine to boot normally.

I ran into the same problem yesterday. However, I could not just replace the video card because this machine had a more powerful card for a certain program. I do not have a video card with similar specs as a replacement.

I tried to re-install the video card driver but to no effect. I tried to install the driver from the manufacturer’s web site; still, it did not work. In the end, I replaced it with a different card just to test. if It worked after the card was replaced. I then took the video card out and put the original video card in. To my surprise, the machine booted up just fine with the original card.

So, if you have this problem, besides trying out the suggestions in those articles, you can try to swap a different video card and then swap back to the original card and see if it works for you.