I had a hard drive sitting around, and I decided to format it such that I could use it in my Linux CentOS box. When I decided to mount it, I got the following error message:

mount: /dev/sdb1: more filesystems detected. This should not happen,
       use -t  to explicitly specify the filesystem type or
       use wipefs(8) to clean up the device.

This message simply tells you that there are two or more file systems sitting in the hard drive partitions, and the system does not know which one to use to mount. We can take a closer look to see what’s going on:

sudo wipefs /dev/sdb1


offset               type
----------------------------------------------------------------
0x2d1b0fa8923        zfs_member   [raid]
                     LABEL: storage
                     UUID:  12661834248699203227

0x951                xfs   [filesystem]
                     UUID:  90295123-2395-7456-8521-9A1EE963ac53

As you can see, we have two file systems here. The easiest way is to wipe out the first few sectors of your disk, i.e.,

sudo dd if=/dev/zero of=/dev/sdb bs=1M count=10

And we will re-do everything again, i.e.,

sudo parted /dev/sdb1
...
...
sudo mkfs.xfs /dev/sdb1
sudo mount /dev/sdb1 /mnt/

That’s it!

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Today I reboot my CentOS 6 server, and I realized that the network connection was lost after the upgrade. To be exact, it seems that the problem was caused by the new kernel: 2.6.32-573.1.1.el6.x86_64. It modified the network settings of the server with manual settings (server with DHCP is not affected). Here is how I fix the problem (You will need physical access to the server):

I have noticed that the adapter profile has been modified to something that doesn’t make scenes. If you compare the network settings, you will notice the following differences:

#Before the upgrade
#cat /etc/sysconfig/network-scripts/ifcfg-em1  
PREFIX=24
#After the upgrade
#cat /etc/sysconfig/network-scripts/ifcfg-em1  
PREFIX=32

So I simply make the modifications to the adapter settings and restart the network service, i.e.,

sudo service network restart

And the network connection is back!

That’s it! Hope this tutorial saves you from heart attack.

–Derrick

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CentOS 7 was released about a week ago, so I decided to give it a try. As you probably know, CentOS is a clone of Red Hat Enterprise Linux(RHEL). Typically, Red Hat put the new features in Fedora first. If things go well, they will move the new features to the RHEL, which eventually will be available in CentOS. In this new version, I see a lot of familiar features which I found in the last few release in Fedora, such as the new GNOME shell, new system service, Linux Kernel 3, etc. However, since RHEL/CentOS is target to enterprise users, who want nothing more than stability and reliably. They put a lot of effect to maintain the backward compatibility, such as /etc/rc.local, firewall etc. Personally, I really like these kind of extra care because it doesn’t break my existing settings.

CentOS 7 EPEL Repository Location

sudo rpm -Uvh http://dl.fedoraproject.org/pub/epel/7/x86_64/e/epel-release-7-1.noarch.rpm

sudo rpm -Uvh http://rpms.famillecollet.com/enterprise/remi-release-7.rpm

And don’t forget to enable the new repository in the config file, i.e.,

sudo nano /etc/yum.repos.d/remi.repo

[remi]
....
enabled=1 ----------------- Set this to one
...

Notice that there are some common packages that were available in these repositories in CentOS 5/6, but missing in CentOS 7, such as hddtemp. So please don’t be surprised that your favorite packages are missing. However, you can always install all of these special packages from source.

–Derrick

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