Jamie Fargen's Weblog

The post is from the stand point of RHEL hypervisor with a KVM CentOS Linux guest using a raw image file as a backing store and the openssl package, but it could easily be applied to different distros, backing stores, or even booting a Linux livecd as long as you can get the necessary packages. Some steps may vary depending on what kind of backing store you are using for the image and the partitions your OS is installed. This process could also be used to do many other things like increasing the time for password expirations.

 

First mount the image as a loopback device:

$ sudo losetup /dev/loop0 /var/lib/libvirt/images/virtcort011ccxra.img       # note that is a zero at the end of /dev/loop

Next add the partition mappings:

$ sudo kpartx -av /dev/loop0

In my CentOS installation I was using LVM and the next few steps are LVM specific:

Use vgscan to find the LVM volume

$ sudo vgscan

This located the new LVM volume group VolGroup00   # again note that is zero zer at the end of VolGroup. You will use this group in the next step.

Activate LVM Volume Group:

$ sudo vgchange -ay VolGroup00

You can use lvs to find the Volume where your / (root) file system is mounted:

$ sudo lvs

Next mount the volume:

$ sudo mount /dev/VolGroup00/LogVol00 /mnt/linuxrescue

You should be able to see directories in the volume:

$ ls /mnt/linuxrescue

Now generate the new password for the guest:

$ openssl passwd -1 -salt ranNum    # for the salt substitute random numbers and letters for ranNum.

Password:

$1$ranNum$N6s5hhYltlYQPnMDdxYy1   # you can see your salt + hash

Now copy this string into /etc/shadow:

$ sudo vi /mnt/linuxrescue/etc/shadow

In editing your shadow file you will see something like below your salt+hash should be  substituted as below for the user password you would like to reset.

root:$1$ranNum$N6s5hhYltlYQPnMDdxYy1:15492:1:90:7:::

If you want to change the length of time for password expirations the next step will show you how.

$ sudo vi /etc/login.defs     # find the value PASS_MAX_DAYS and edit it to your needs

Now unmount the file system:

$ sudo umount /mnt/linuxrescue

Unactivate the LVM vol group:

$ sudo vgchange -an VolGroup00

Delete the partition mappings:

$ sudo kpartx -dv /dev/loop0

Unmount the loopback device:

$ sudo kpartx -dv /dev/loop0

 

The post is from the stand point of RHEL hypervisor with a KVM Windows guest using a raw image file as a backing store using the package chntpw, but it could easily be applied to different distros, backing stores, or even booting a Linux livecd as long as you can install the chntpw package. Some steps may vary depending on what kind of backing store you are using for the image and where your Windows OS was installed.

First get the chntpw package:
$ sudo yum install chntpw

Print the logical loopback device:
$ sudo losetup -f
/dev/loopo

Next mount the image file as a loopback device:
$ sudo losetup /dev/loopo /var/lib/libvirt/images/windows7.raw

Add partition mappings:
$ sudo kpartx -av /dev/loop0  #That is a zero at the end of /dev/loop0

Create a directory that can be used as a mount point:
$ sudo mkdir -p /mnt/winrescue

Mount the appropriate filesystem:
$ sudo mount /dev/mapper/loop0p2 /mnt/winrescue

Change to the directory where the SAM db is located:
$ sudo cd /mnt/winrescue/Windows/System32/config/

Now run the chntpw utility:
$ sudo chntpw -I SAM

Once complete you will want to unmount the filesystem and loopback device.

Get out of the mounted filesystem:

$ cd ~

Umount the filesystem:

$ sudo umount /mnt/windowsrescue/

Delete the partition mappings:

$ sudo kpartx -dv /dev/loop0

Unmount the loopback device:

$ sudo losetup -d /dev/loop0

The process is now complete.

Say you have 1 file that is 10TBytes, like a VM image, that you need to copy between say two nfs file stores (that you don’t control). Your only problem is a single host is only capable of 50MB/sec over a 1Gb/sec network connection. The good news is you have hundreds of hosts all mounting these two nfs filesystems. Maybe you can lash 10-12 hosts together to greatly the reduce the time it takes to copy the file? Then check out scp-tsunami – http://code.google.com/p/scp-tsunami.

Hopefully one day you won’t come upon a server running ESX / Linux that has become unresponsive to regular management tools and view something like this completely filling your console:

sd 7:0:2:0 still retrying after 360s

I knew instantly 7:0:2:0 was a SCSI mapping for host, bus, scsi id, etc, etc. These hosts are using SATA drives and I needed to be able to us hdparm to determine the serial number of the drive for local support to replace.  After digging I came up the command sg_map matched with -x option prints after each active sg device name is displayed there are five digits: <host_number> <bus> <scsi_id> <lun> <scsi_type>.

When I ran sg_map -x this provided me with exactly what I need: /dev/sg2  7 0 2 0  0  /dev/sdc.  You can see that sdc is mapped to SCSI address 7:0:2:0. With this information I was able to use hdparm -i /dev/sdc to extract the serial number of the drive and provide it to local hands and feet support in Germany to swap out the failing hard drive.

A lot of people do backups with rsync and 99% of the time it works pretty well. There is one file type that rsync handles rather poorly and that is sparse files, even though rsyncs documentation indicates that sparse files are handled efficiently it is simply not true. These sparse files are becoming more prominent because they are used to store VM images, like KVM, Xen, even VMWare. So what is a good way to copy them? It turns out that tar is much better at handling sparse files than rsync, it has had support for sparse files for over two decades, and can represent the holes in sparse files more efficiently.

In my testing using Tar instead of Rsync has resulted in cutting the time to backup a sparse file by 8-10 times.

Just pipe tar over ssh and compare your results to rsync:
tar cvzSpf – sparse.file | ssh user@hostname ‘(cd /tmp; tar xzSpf -)’

 

Start off by writing your text using the visual editor. Once your text has been entered go to the Youtube video you would like displayed and click the embed button, there are some settings below allowing you to configure the layout. Copy the embed code which should look something like this:

<iframe title=”YouTube video player” width=”425″ height=”349″ src=”http://www.youtube.com/embed/bsjbkOX7gUA?rel=0″ frameborder=”0″ allowfullscreen></iframe>

Next click the HTML tab in the Add New Post editor and copy and paste this iframe code above or below your text depending on the desired layout. You can then preview the page and change back to the Visual tab of the editor if you need to change the text or layout. Wash, rinse, repeat.