CentOS Remove Old Kernels

Tonight when upgrading a CentOS Linux server it was noted by YUM that 15MB more disk space was needed to upgrade grub and the kernel itself. Below are four quick steps to verify what kernels are installed, install yum-utils if it is not installed already, delete previous kernels and set YUM to remove old kernels…

Technology Insights

Ubuntu apt-get upgrade – The following packages have been kept back

When upgrading packages on Ubuntu using the apt-get upgrade command you may notice that some packages are not upgraded. Ubuntu will not upgrade packages that could have a major impact to service on the server such as the kernel, kernel headers, MySQL packages, and various others. The packages are held back by aptitude as a safeguard to keep people from upgrading packages that might keep the server from rebooting or that might corrupt something like a database. Below we show the error in more detail and explain the command that can be run to upgrade the packages that are being held back.

Technology Insights

JTR – John The Ripper Compile Error – /usr/bin/ld: cannot find -lOpenCL

The article below describes an error received while attempting to compile John The Ripper with GPU support via OpenCL on Ubuntu Linux version 12.04 LTS also known as Precise Pangolin. Many compile errors are related to necessary packages not being installed on Linux though other errors could be related to all sorts of different issues such as incorrect Library versions or files in the incorrect locations. In this case the specific error states that ld cannot locate the OpenCL library so below we describe the error in more detail, how to search to see if the proper libraries are installed, and the resolution by simply creating a symbolic link to the proper OpenCL library.

Technology Insights

JTR – John The Ripper Compile Error – common-opencl.h:8:19: fatal error: CL/cl.h: No such file or directory

Recently while attempting to get John The Ripper 1.7.9 jumbo-7 working on a Ubuntu 12.04 LTS Linux server with multiple AMD GPU cards in it I ran across an error during the compile process. The error complained about the VL/cl.h file not being installed and thus could not finishing compiling. Below I describe the compile error, how to locate the Ubuntu package that installs the necessary file to move past the previously mentioned compile error, and then how to install the correct package.

Information Security

arping – Backtrack 5 – Information Gathering – Network Analysis – Identify Live Hosts – arping

The arping application is a simple command that will allow you to ping devices by hostname, IP address, or MAC address. The unfortunate part is that most device will not respond to the arp requests, which are directed broadcast ICMP echo requests, though there are some out there that do. I go into more detail below regarding pinging via MAC address by providing an example of the typical output, example output when a MAC address responds to the ICMP echo requests, and details about how to configure hosts to respond to these ICMP echo requests. I also show a couple of the switches available with arping and provide examples of using arping to ping devices by IP and host.