rpm command: list packages

Q. How do I search and query the packages installed on my Linux box using rpm? (OpenSUSE, FedoraCore, Red Hat, CentOS, etc).

A. You can query the packages using:

rpm -qa

This will output all packages installed, if you are looking for a particular package, you can pipe your results into grep. Here's for example a search for all packages that have "kernel" in the name:

rpm -qa | grep "totem"

Save previous choice in GRUB bootloader

Q. I would like GRUB to remember my last OS choice and make that the selected option on the next boot. How do I do that?

A. This example is for GRUB2 - for GRUB 1 the options are slightly different.

Boot into Linux and make a backup of the following file:

sudo cp /etc/default/grub /etc/default/grub.bak

Special device UUID does not exist

Q. I'm trying to mount a drive using UUID, but I get the following error: 

mount: special device /dev/disk/by-uuid/87470c42-4b34-475c-86d0-bf0df06d4f3c does not exist

A. You've just created the new partition and the OS doesn't see it. You can either reboot or run the following command 

sudo partprobe

Convert SSL certificate from CRT format to PEM

Q. Ubuntu 8.04 is setup by default to accept PEM certificates instead of CRT, is there any way to convert it?

A. You can convert the SSL certificates using the following commands:

openssl x509 -in server.crt -out server.der -outform DER

and:

openssl x509 -in server.der -inform DER -out server.pem -outform PEM

Measure disk I/O in Ubuntu

Q. I think I'm having disk I/O problems on my system. How do I check what it is or measure it?

A. First, you'll have to install some applications/tools:

apt-get install sysstat
apt-get install iotop

iotop command, much like top, will give you the real-time overview of your Read/Write requests. It's fun to look at, but we find useless for measuring I/O.

Enable Internet Explorer in Windows 2008 Server

Q. How can I disable all those warning in Internet Explorer on my server and just the browser?

A. You have to disable Internet Explorer Enhanced Security Configuration (IE ESC).

1. To do that, go to Start -> Administrative Tools -> Server Manager