Ansible Facts Caching With Redis

Ansible is an amazing tool for automation of tasks. Facts are details about the host that Ansible gathers when it connect to the machine. It will gather a significant amount of useful information that can be used in Playbooks e.g. OS version, IPv4/IPv6 addresses. To make Ansible go faster we can store the facts in a cache the first time in connects to the hosts. On subsequent Playbook executions Ansible will only look up the facts in the cache instead of gathering them again. There is a cache option fact_caching_timeout that can be modified to define how long the cache should be valid for in seconds.

Setup Redis for Ansible Caching

On Arch Linux install redis and enable it

  $ pacman -S redis
  $ systemctl enable redis
  $ systemctl start redis

Install the Python Redis packages

$ pacman -S python2-redis python-redis

Check redis is responding

$ redis-cli ping
PONG

Update /etc/ansible/ansible.cfg in a text editor

gathering = smart
fact_caching = redis
fact_caching_timeout = 86400
fact_caching_connection = localhost:6379:0

After running a Playbook redis-cli can be used to view the keystore e.g.

$ redis-cli 
127.0.0.1:6379> keys *
1) "ansible_cache_keys"
2) "ansible_factsDB1"

ssh agent and forwarding on Arch Linux for Ansible

I have been using Ansible a lot for automation of deployments recently. One of my deployments had the need to clone a git hosted project from a server in the cloud. I did not want to have to place my private key on the cloud server for security reasons. The answer for me was setting up an ssh agent on my Arch Linux workstation to simplify working for ssh keys. With the ssh agent in place I could use ssh agent forwarding to authenticate using the private key on my workstation. The same process would work for any version of Linux.

SSH Agent set-up

On the Arch Linux Wiki there is a number of suggestions but the one I found was the easiest was from this StackOverflow article by adding the following to my ~/.bash_profile

SSH_ENV="$HOME/.ssh/environment"

function start_agent {
echo "Initialising new SSH agent..."
/usr/bin/ssh-agent | sed 's/^echo/#echo/' > "${SSH_ENV}"
echo succeeded
chmod 600 "${SSH_ENV}"
. "${SSH_ENV}" > /dev/null
/usr/bin/ssh-add;
}

# Source SSH settings, if applicable

if [ -f "${SSH_ENV}" ]; then
. "${SSH_ENV}" > /dev/null
ps -ef | grep ${SSH_AGENT_PID} | grep ssh-agent$ > /dev/null || {
    start_agent;
}
else
start_agent;
fi

This will check if you already have an ssh-agent running and if not will start a new agent. You can always check its running:

$ pgrep -a ssh-agent
23409 /usr/bin/ssh-agent

The ssh-agent daemon will automatically import the private key ~/.ssh/id_rsa which can be listed with:

$ ssh-add -L

Other private keys can be included for use by the ssh-agent with :

$ ssh-add <path to private key>

Agent Forwarding

Within my /etc/ansible/ansible.cfg file I set the following ssh settings

[ssh_connection]
ssh_args = -o ControlMaster=auto -o ControlPersist=60s -o ForwardAgent=yes

When Ansible is on the remote machine and clones from the git project the authentication will automatically be forwarded to my Arch workstation to be authenticated by the ssh-agent.

Obtain Random Words from a Dictionary in Linux

It can be very useful to be able to quickly generate random words from a dictionary in Linux. One common use case I have is generating random responses for the Security Questions on web sites. This is to avoid anyone easily guessing what the answers are. Typically the questions tend to be the same and not very difficult to guess. I save the actual responses in the Notes section of the Password Manager than I use.

Obtain A Dictionary Text File

There is a great dictionary list that is available with GNU Aspell (ftp://ftp.gnu.org/gnu/aspell/dict/0index.html) which provides a collection of International ‘words’ files for /usr/share/dict.
To install on Arch Linux :

$ pacman -S words
$ wc -l /usr/share/dict/usa
119095 /usr/share/dict/usa

There are a number of dictionaries installed under /usr/share/dict/ that you can choose from

$ ls /usr/share/dict/
american-english british british-english catala catalan finnish french german italian ngerman ogerman spanish usa

shuf - generate random permutations

We can use the shuf command to generate random words using a dictionary. Install shuf if its not installed :

$ pacman -S shuf

Then use the n argument to define the number of words you would like e.g.

$ shuf -n5 /usr/share/dict/usa
macroeconomic
visualizes
shabbiest
sen
chortler

To easily access this I have an alias :

alias GenerateRandomWord=’shuf -n5 /usr/share/dict/usa’

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How To: Automatically cd to a directory after you create it

The majority of the times that I create a directory I would then change to that directory. To make this happen automatically I add the following to my .bashrc :

mkcd () { mkdir -p "$@" && eval cd "\"\$$#\""; }

Example :

$ mkcd ~/tmp/FOO

$ pwd

/home/cw/tmp/FOO

How To: Display your Top 10 cli commands




Its useful to be able to see which command you use most often on a Linux box. I add the following to my .bashrc :

cli-top-10() {

  history | awk '{a[$2]++ } END{for(i in a){print a[i] " " i}}' | sort -rn | head

}

Example output :

57 ls

49 cd

26 mv

25 curl

18 wget

17 rm

15 sudo

13 packer

12 docker

12 vim

How To: Permanently Display line numbers for Vim or Vi

It can be very useful when troubleshooting to display line numbers in Vim or Vi. To enable this in your ~/.vimrc file add :

:set number

which can also be manually set within Vim or Vi. Within the editor to remove the line numbers :

:set nonumber

VirtualBox slow on installation of Guest OS

I use VirtualBox for testing in many environments. Normally the defaults are fine for installing Linux but on one environment it was really slow to just install. Installing Debian Jessie from an ISO would normally take 15 minutes but in this environment after an hour it was still only at 35%. The host OS was not over taxed and has lots of spare CPU + RAM resources free.

After some testing I found the issue was resolved by :

1. Open Settings
2. Navigate to System->Motherboard
3. Change the Chipset to ICH9 (see below)
4. Press OK

Now the installation will be fast.