openssl version -a
OpenSSL 1.0.1e 11 Feb 2013
built on: Mon Apr 7 20:33:19 UTC 2014
If build on line says Apr. 7 or after: you're good. Otherwise: you're in trouble.
UBuntu and Debian
On Ubuntu and Debian, you can update by typing:
sudo apt-get update
sudo apt-get dist-upgrade
If you only want to upgrade the affected packages, and not update the entire system (only recommended if you have reason to believe that upgrades to other components will break your system), you can selectively upgrade the OpenSSL packages by typing:
sudo apt-get install --only-upgrade openssl
sudo apt-get install --only-upgrade libssl1.0.0
This will upgrade the vulnerable packages while leaving the rest of your system in an un-upgraded state.
CentOS and Fedora
On CentOS and Fedora, you can type this to update the entire system:
If you wish to only upgrade the affected package, you can instead issue this command:
yum update openssl
Again, this is only recommended if you have a specific reason for not updating the complete system.