Random notes go here!

This might feel a little redundant to the hacks section, and truthfully a lot of things that I add here, I might also include there. The main difference is that I'm going to strive to only put things here which are setup in a more reusable way. If it doesn't work out, I'll probably end up combining the sections later.

Articles on Notes

Docker Tips

Here are a few tips that I've found useful while delving in to Docker. For an introduction to Docker, see my post on the YP Engineering Blog. Enjoy!

Making smaller images.

Docker image size does matter. The larger your image, that more unweildy it starts to feel. Pulling a 50MB image is far preferable to pulling a 2G image. Some tips on building smaller images:

  • Use the smallest linux distro which meets your needs; busybox < debian < centos < ubuntu. I try to use progrium/busybox whenever possible (which isn't all that often without serious work), otherwise, I tend to use debian.
  • Install as little as possible to meet your needs -- apt-get build-essential is going to bloat your image, don't use it unless absolutly necessary.
  • Do as much as you can in a single RUN, as opposed to breaking things up. The downside to this is longer builds with less caching. However, it can make a huge difference in resulting image size. I once took an image from 1.3G to 555MB, just by collapsing all my commands to a single RUN. Additionally, clean up after yourself in that same RUN if possible. Example:

      # BAD
      RUN apt-get install git
      RUN apt-get install wget
      RUN apt-get install build-essential
      RUN tar xzf somefile.tgz
      RUN cd somefile
      RUN ./configure && make && install
      # GOOD
      RUN \
          apt-get install -y git wget build-essential && \
          curl -sSL -O && \
          tar xzf somefile.tgz && \ 
          cd somefile && ./configure && make && install && \
          cd - && rm -rf somefile somefile.tgz && \
          apt-get remove -y build-essential && \
          apt-get autoremove -y && apt-get clean

Search private registry.

sudo docker search <private domain>/<term>

Removing images and containers in bulk.

# remove all containers
sudo docker rm $(sudo docker ps -a -q)
#... or ...
sudo docker ps -aq | xargs sudo docker rm

# remove all images
sudo docker rmi $(sudo docker images -q)
#... or ...
sudo docker images -q | xargs sudo docker rmi

# remove specific images in bulk
sudo docker rmi myimage:{tagone,tagtwo,tagfive}

# remove image containing TERM
sudo docker rmi $(sudo docker images | grep TERM | awk '{ print $3 }')
#... or ...
sudo docker images | grep TERM | awk '{ print $3 }' | xargs sudo docker rmi

# remove all non-running containers
sudo docker ps -a | grep Exited | awk '{ print $NF }' | xargs sudo docker rm

Interacting with the most recent continer started.

# view last container
sudo docker ps -l 

# view last container sha only
sudo docker ps -lq

# stop, start, attach, logs, etc. last container
# $ sudo docker <action> $(sudo docker ps -lq)
sudo docker start $(sudo docker ps -lq)
sudo docker stop $(sudo docker ps -lq)
sudo docker logs $(sudo docker ps -lq)
sudo docker attach $(sudo docker ps -lq)

Pushing to a private registry.

# assuming image 'jmervine/centos6-nodejs'
#               <current image name>    <private registry>:<port>/<image name>
sudo docker tag jmervine/centos6-nodejs
sudo docker push

# I then recommend removing your old image to avoid accidentally pushing it to the public registry.
sudo docker rmi jmervine/centos6-nodejs


# running randomly assigning host port
sudo docker run -d -p 3000 image/name

# running with exposed ports randomly assigned on host
sudo docker run -d -P image/name

# printing randomly assigned ports (only)
sudo docker port image_name | awk -F':' '{ print $NF }'

Copying Files TO Containers

# Directly in to a running container.
sudo docker exec -it <container_name|name> \
    bash -c "echo \"$(cat /path/to/host/file.txt)\" > /path/to/container/file.txt"

# When running a container.
sudo docker run -i <container_id|name> \
    bash -c "echo \"$(cat /path/to/host/file.txt)\" > /path/to/container/file.txt; /bin/bash ./"

# Via Docker volume.
# - where 'file.txt' is /path/to/host/dir/file.txt
sudo docker run -v /path/to/host/dir:/path/to/container/dir <container_id|name>

#... or ...
sudo docker run -v /path/to/host/dir:/path/to/container/dir <container_id|name>
cp /path/to/host/file.txt /path/to/host/dir/file.txt

# Via file system -- untested as of yet.
sudo cp -v /path/to/host/file.txt \
    /var/lib/docker/aufs/mnt/**$(sudo docker inspect -f '{{.Id}}' <container_id|name>)**/root/path/to/container/file.txt

Based on comments in

Building Docker Machine

What's Docker Machine?

Machine makes it really easy to create Docker hosts on local hypervisors and cloud providers. It creates servers, installs Docker on them, then configures the Docker client to talk to them

This wasn't as clear as I was hoping, so here's what I did.


$ uname -sm
Darwin x86_64

$ docker version
Client version: 1.3.0
Client API version: 1.15
Go version (client): go1.3.3
Git commit (client): c78088f
OS/Arch (client): darwin/amd64
Server version: 1.4.1
Server API version: 1.16
Go version (server): go1.3.3
Git commit (server): 5bc2ff8

$ mkdir -p $GOPATH/src/
$ cd $GOPATH/src/
$ git clone
$ cd machine

$ make test
$ ./script/build -os=darwin -arch=amd64
$ mv docker-machine_darwin-amd64 $GOBIN/docker-machine


$ uname -sio
Linux x86_64 GNU/Linux

$ sudo docker version
Client version: 1.4.1
Client API version: 1.16
Go version (client): go1.3.3
Git commit (client): 5bc2ff8
OS/Arch (client): linux/amd64
Server version: 1.4.1
Server API version: 1.16
Go version (server): go1.3.3
Git commit (server): 5bc2ff8

$ mkdir -p $GOPATH/src/
$ cd $GOPATH/src/
$ git clone
$ cd machine

$ sudo make test
$ sudo ./script/build -os=linux -arch=amd64
$ sudo chown $USER: docker-machine_linux-amd64
$ mv docker-machine_linux-amd64 $GOBIN/docker-machine

Simple Timing in Node.js

I just stumbled upon a cool feature of Node.js for adding timing to applications using console.time and console.timeEnd`.

// pointless example that show all parts
setTimeout(function() {
}, 500);

// => timer: 511ms

Note: I've heard (and in somecases proven) that in most cases console. method are not asynchronous (i.e. blocking) and therefore should never be used in production code. Notice that in the above example, console.time and console.timeEnd appear to have about 11ms of overhead on my machine.

Jade Bootstrap Layout Template

After using the Express command line generation untility, you get a very basic layout.jade. Here's the standard modifications I make for use with BootstrapCDN.

Notes: Mosh IPTable Rules

I recently picked up a Note 3 and with the larger screen I found myself want to use it for shelling in to my machines. So I started playing with Mosh on one of my boxes. I (like hopefully most of you) set strick IPTable rules to keep things locked down as much as possible. I quickly found that (obviously) things weren't working due to this.

To make things work, I added this line to /etc/sysconfig/iptables:

-A INPUT -p udp -m udp --dport 60001:61000 -j ACCEPT

Here's the diff:

diff --git a/tmp/iptables.old b/etc/sysconfig/iptables
index d4229ca..b950f1f 100644
--- a/tmp/iptables.old
+++ b/etc/sysconfig/iptables
@@ -8,6 +8,7 @@
 -A INPUT -p icmp -j ACCEPT 
 -A INPUT -i lo -j ACCEPT 
 -A INPUT -p tcp -m state --state NEW -m tcp --dport 22 -j ACCEPT 
+-A INPUT -p udp -m udp --dport 60001:61000 -j ACCEPT
 -A INPUT -j REJECT --reject-with icmp-host-prohibited 
 -A FORWARD -j REJECT --reject-with icmp-host-prohibited 

Once you've added the line, simply restart IPTables like so:

sudo /etc/init.d/iptables condrestart 


Notes: JavaScript `median(Array)`

function median(values) {
    values.sort( function(a,b) {return a - b;} );
    var half = Math.floor(values.length/2);
    if (values.length % 2) {
        return values[half];
    } else {
        return (values[half-1] + values[half]) / 2.0;

Notes: Disable SSH Strict Host Checking

What automating tasks with ssh, it can be annoying to be prompted to confirm the authenticity of host.

The authenticity of host ' (NN.NN.NN.NN)' can't be established.
RSA key fingerprint is af:78:f8:fb:8a:ae:dd:55:f0:40:51:29:68:27:7e:7c.
Are you sure you want to continue connecting (yes/no)? 

Here's a simple way around that:

# This automatically adds the fingerprint to 
# ~/.ssh/known_hosts
ssh -o StrictHostKeyChecking=no

# This doesn't add fingerprint
ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no

Notes: Finding Older Files

In this example, I'm finding all files older then 14 days and removing them.

$ find . -type f -mtime +14 | xargs rm

In this example, I'm finding top level directoies in /foo/bar/bah that are more then 30 days old and removing them.

$ find /foo/bar/bah -type d -mtime +30 -maxdepth 0 | xargs rm -rf

I typically use this for removing, which is why I've used that as an example. This type of thing is great for a cronjob...

# remove old files daily at 1am
* 1 * * * find /foo/bar/bah -type d -mtime +30 -maxdepth 0 | xargs rm -rf

Stubbing Binaries for Testing

Being a Dev Ops guy, I write gems, scripts and hacks that tend to hook in to system binaries. I know, it would probably be better to write C bindings, but heretofore that hasn't been something I really want to tackle. Additionally, I almost always write tests for my stuff. I've come across the problem where my tests pass locally, but not on Travis-CI.

WiFi/Bluetooth Hack for the HP Folio 13

Someone asked for this recently, I'm not going to go in to great detail at this time, but I found it while looking through my gists and thought I would share.

Simple replace your /etc/rc.local with the following and it should unlock the hardware airplane mode on startup.

#!/bin/sh -e
# rc.local
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
# In order to enable or disable this script just change the execution
# bits.
# By default this script does nothing.

rfkill unblock wifi
sleep 5
rmmod -w -s hp-wmi
#modprobe -r -s hp-wmi

exit 0

get the gist

Node.js forever handing via make


  • start :: starts application using forever
  • stop :: stops application using forever
  • restart :: restart application using forever

    # This set's your local directory to to your NODE_PATH
    # This is for local (non `-g`) npm installs.
    # NODE_MODS    = ./node_modules/.bin
    # Some good `forever` options.
    FOREVER_OPTS = -p ./logs  \
                    -l server_out.log \
                    -o ./logs/server_out.log \
                    -e ./logs/server_err.log \
                    --append \
                    --plain \
                    --minUptime 1000 \
                    --spinSleepTime 1000
    start: setup/dirs
        # starting app in server mode
        $(NODE_EXEC) $(NODE_MODS)/forever $(FOREVER_OPTS) [email protected] server.js
        # stopping app in server mode
        $(NODE_EXEC) $(NODE_MODS)/forever $(FOREVER_OPTS) [email protected] server.js
    restart: setup/dirs
        # restarting app in server mode
        $(NODE_EXEC) $(NODE_MODS)/forever $(FOREVER_OPTS) [email protected] server.js
        # creating required directories for `forever`
        mkdir -p logs pids

Get the gist.

Installing Node.js from Source

Note: This has been tested on Ubuntu 12.01. It should also work on most CentOS (Redhat) version and Mac's, but I haven't personally tested it.

Copy and save this to a script called something like and run bash It expects sudo access.

#!/usr/bin/env bash
set -x
cd /tmp
rm -rf node

set -ue
git clone git://

cd node
git checkout v0.10.20

./configure --prefix=/usr
sudo make install

# vim: ft=sh:

Get the gist.

Hello World: Sinatra vs. Node.js


require 'sinatra'
get '/' do
  "Hello World"


var app = require('express');
app.get('/', function(req, res) {
    res.send("Hello World!");

Install MySQL on CentOS 6

A simple script to install MySQL on CentOS 6.

# sudo bash < <(curl -s

set -x
cd /tmp

rpm -qa | grep mysql-libs && yum remove -y mysql-libs

yum install -y MySQL-shared-5.6.10-1.el6.x86_64.rpm
yum install -y MySQL-client-5.6.10-1.el6.x86_64.rpm
yum install -y MySQL-server-5.6.10-1.el6.x86_64.rpm
yum install -y MySQL-devel-5.6.10-1.el6.i686.rpm

Link to gist.