ikarandeep.

I recently installed an SSD in my machine which meant I had reinstall OS X.

After downloading the OS X Dropbox app and syncing the directories I wanted, I noticed that my directories I had setup as symlinks were not working "out of the box".  I had my Documents & Desktop symlinked to Dropbox.  To fix it I did the following:

1. Pause dropbox from syncing

2. Open terminal and rename the directory you had symlinked to something else.  I had a directory called "documents symlink".

$ mv "Dropbox/documents symlink" Dropbox/temp

3. Create a new symlink

$ ln -s "/Users/karandeepsingh/Documents "Dropbox"

4. Rename the newly created "Documents" symlink that is in your Dropbox directory

$ mv Dropbox/Documents "Dropbox/documents symlink"

5. Move all the files from temp to documents symlink

$ mv Dropbox/temp/* Documents/

Thats it!

I wanted my page to have a full width.  I set it as so in the CSS:

body{width: 100%;}

However, this actually made the page width look bigger than 100%.  The horizontal scroll bar existed even when the entire page was visible.

The fix?

Throw all the content into a class called .container-fluid:

<div class="container-fluid">

<!---content here-->

</div>

I love to send GIFs to my co-workers, however, there is a 500 kb limit on the size of the GIF.  This brings me to my latest hack...

https://gifs.ng.bluemix.net https://gifs.mybluemix.net

A weird looking URL, right?  Instead of using Heroku or Openshift, I decided to build my app on IBM's PaaS, BlueMix.  Why? I use BlueMix daily at work so I felt most comfortable with it.

However, before this I had absolutely no experience with combination Django + Python + BlueMix.  Infact, I've only used Django a few times.  This would be fun.

Using the Giphy API, I quickly built a script to grab the data I wanted and search for GIFs under an N size.

The next step would be implement it into a Django web application on my machine.  This part was fairly easy.

Finally I wanted to deploy my app to BlueMix.  BlueMix uses buildpacks to deploy. Similar to Heroku.  It doesn't support Python right out of the box.  After some googling and various attempts I was able to launch my app.

I tried a few different buildpacks and finally found one that worked: https://github.com/ephoning/heroku-buildpack-python

Another key requirement to deploying onto BlueMix is the "requirements.txt" file.  This file lists the dependencies that are needed to run the application.  Here's mine.

Also, BlueMix chooses the port number to run the application.  Luckily they provide the port number in an Environment Variable.  However, getting it to work took me some time.  I ended up coming across this shell script.  I modified it and created my own here.  When pushing the app to BlueMix, we provide the appname, buildpack, and the start command (the shell script which runs "manage.py runserver" with the port we need).

Using the following command, I was finally able to launch my app :)

$ cf push gifs -b https://github.com/ephoning/heroku-buildpack-python -c "sh run.sh"

If you're deploying an app on BlueMix with Python and Django, be sure to do the following:

1. Use this buildpack

2. Add a requirements.txt file to the root of your app with all the dependencies listed out

3. Include a shell file to start the server

I've learned that one of the best ways to understand something is to teach it.  Lately I've been spending time learning different algorithms.  The very basic sorting algorithm is Insertion Sort.  It basically works like this:

You have an array of unsorted numbers that you want to sort in either ascending or descending order.  You iterate through each item in the array checking to see whether its greater (or less than) the current number (the key).

Example in psuedocode:

// a list or array of numbers

nums[9,3,6,2,5,7,1,8]

// iterate through the list

// the index will be 0, 1, 2, 3, etc (the position in the array)

// we want to go through each position hence the <length of nums>

for index <the index of each number> in the range of <length of nums>

        // create a key and set it to the item at the current index

        key = nums[index]

       // initalize another variable called i because we need to iterate through the array again but starting at one lower than the current index

        i = index - 1

         // we need a while to check to see if the key is smaller than the number after it...if its smaller, then we should keep going through this loop. Once the key is bigger than the num[i], then we exit the loop

        while i >= 0 and num[i] > key

              // put num[i] into the num[i+1] position

              num[i+1] = num[i]        

             // decrease the i

             i = i -1

// once we are out of the loop, its because num[i] is less than the key, so we can move the key to the num[i+1] position

     num[i+1] = key 

  Here's the code in python with my comments on Github

Dropbox is some pretty great software.  However, copying files into the "Dropbox" folder is quite a hassle.  Luckily, Dropbox allows us to create symlinks to other directories to easily sync them.  Here's a link to a script I wrote that will easily do it.

Here's the command:

$ ./dropboxSymlinks.sh /Users/karandeep/Documents/code /Users/karandeep/Dropbox

https://github.com/ikarandeep/dropboxsymlink

Run this before syncing the Selected folder from Dropbox.  For example, if you have a "photos" directory in Dropbox and you want it in your "Documents" directory, do the following:

$ cd Documents

$ mkdir photos

$ ls

It's output is kind of boring. You get a simple list of files.  Not very useful sometimes.  What if you want to see more.  You want to know permissions, who created it, a modification date, and in order.  Try this:

$ ls -lrta

the "l" displays the files in a nice column format

the "r" reverses the order in which they are listed

the "t" sets the ordering by modification date

the "a" displays everything including hidden

It's annoying to remember passwords and host names when logging into servers.

Typically to ssh into a server we would need to enter:

$ ssh server.karandeep.com

But if the username on the account didn't match the current user on the local machine we'd have to login like this:

$ ssh [email protected]

Then we would be prompted to enter a password.

 There's a way we can easily get around this.  Enter the "config" file.

The config file is stored in the .ssh directory, the same place we store our private key and public keys.  

The first thing we need to do is generate a public-private key pair if we do not have one. You can easily do this by running the following command:

$ ssh-keygen

Generating public/private rsa key pair.

Enter file in which to save the key (/home/karandeep/.ssh/id_rsa):

Enter passphrase (empty for no passphrase):

Fill in the details.  A passphrase is optional.

This will produce two files for you.  A public key and a private key.

The public key: this goes on your server that you want to login to.

The private key: this lets you access a server that has your public key.

So now lets copy over that public key to our server.  We can easily do that in a few simple commands:

1. ssh into the server

$ ssh [email protected]

2. create the .ssh directory if it does not exist.  Note that "." before "ssh"

$ mkdir .ssh

3. in a separate terminal, run the following to copy over the key

$ cat ~/.ssh/id_rsa.pub | ssh [email protected] 'cat >> .ssh/authorized_keys'

4.  make sure the permissions are correct.  if the permissions are wrong, you will be required to enter a password. The ".ssh" directory should be 700 and the files should be 600

$ chmod 700 .ssh

$ chmod 600 .ssh/*

Now the keys should be all setup.  You should be able to easily login to the server without a password.  Go ahead and try it:

$ ssh [email protected]

Success!

But now wouldn't it be cool to just login without having to enter all of that?  I want to be able to enter "ssh test" to login to my test instance.

Here's how we can do that with the config file:

1. Create a config file in the .ssh directory

$ vi .ssh/config

2. Enter the following information

Host (the nickname we are using)

HostName (fully qualified hostname)

IdentityFile (location of your PRIVATE key)

User (theuser to login with)

See the example below:

Host test HostName server.karandeep.com IdentityFile ~/.ssh/id_rsa User karandeep

3. Save the file by enter ":wq!"

Now try to ssh into the server with the following command:

$ ssh test

You should now be logged in! No need to remember host names or passwords or wasting time typing in things.  You can also sftp with the config file!

Hope you found this useful :)

Troubleshooting & notes

1. check permissions on the files.  The public and private key should both be 600