Saturday, June 9, 2012

Mounting a USB Device In a Xen Guest

​Mounting a USB device
 Attach the USB device to the Dom0 and run ‘dmesg’ to see if the device attached
 Run ‘fdisk -l’ to see if the drive is partitioned the way you want it
 For instance:
[[email protected] ~]# fdisk -l /dev/sdc
Disk /dev/sdc: 1000.2 GB, 1000204886016 bytes
255 heads, 63 sectors/track, 121601 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
dev/sdc1 1 121601 976760001 8e Linux LVM
Now find a drive letter that is not being used on the DomU, in this instance we’ll use /dev/sde
To attach the USB device to the DomU run the following command
    xm block-attach exampledomu phy:/dev/sdc sde w
You should now see the device on the DomU, run either ‘dmesg’ or ‘fdisk -l’ to verify
Mount the device as normal
    mount /dev/sde1 /mnt/usb
Unmounting the device
You first need to get the device id number from the block list. Do this by running:
    xm block-list exampledomu
This will return:
    Vdev BE handle state evt-ch ring-ref BE-path
    51712 0 0 4 9 8 /local/domain/0/backend/tap/23/51712
    2176 0 0 4 10 1338 /local/domain/0/backend/vbd/23/2176
The number you need to use to remove the device is 2176
Unmount the USB device from the DomU
     umount /mnt/usb

 Now on the Dom0 run:
     xm block-detach exampledomu 2176
 You may now remove the USB device

Getting Linksys AE2500 to work with Fedora 17

​In order to get the AE2500 wireless USB adapter to work you must install ndiswrapper. First, the ndiswrapper-1.57 version is not compatible with the 3.3 or 3.4 version of the Linux kernel so you must install the ndiswrapper-1.58rc1 which is still in test as of this writing. Next, download the AE2500 Windows XP drivers from the Linksys website ( Link ). Unzip the drivers into a directory and load the bcmwlhigh5.inf file into ndis. Once this is done, you can run the 'ndiswrapper -l' command to verify that it is installed correctly. Finally, run 'modprobe ndiswrapper' to load the driver into the kernel. Once this is complete you should see the wireless USB device come up as wlan0 and ready for use.

Saturday, June 2, 2012

MySQL Backup Script

I needed a place to host my scripts, so I opened an account on GitHub. If you are unaware of what GitHub is, its a great place to publish code to the public by using Git; they also offer private hosting for a fee. Even if you do not have a need for this I recommend looking through the site as its a great place to view open source projects.
There are a lot of examples and scripts out on the Internet to automate MySQL backups but not a whole lot written in Python. This was developed to use in a MySQL replication environment and should be run on the slave server. This is an optimal solution as backup’s can run without affecting production. The script dumps each database individually, calculates the size of the sql backup, tarball them up, and emails a log when its done.
To run this the MySQLdb module must be installed on the server. You should also create a user specifically designed to run backups. You can effectively do this by running:
    grant select, lock tables on *.* to backup@'localhost' identified by 'password';
The password is stored in base64 format. To encrypt the password for use in the script, run the following command within the Python terminal:
    >>> from base64 import b64encode as encode
    >>> encode("password")
    'cGFzc3dvcmQ='
Though this is not the most secure way to encrypt a password to use within a script, it will prevent shoulder surfers.