Quick Tip: How to convert a pdf into an image file using ImageMagick

The other day I needed to convert a pdf document into an image file using ImageMagick and here are a few things I learned. Note: The following conversion examples were performed in the Linux terminal but ImageMagick is not limited to a Linux OS.

How to convert a single-page pdf into an image file:

convert file.pdf file.png

How to convert a multi-page pdf into multiple image files:
Note: The following command will output image files where the file names will following the pattern file_pg_#.png. e.g. file_pg_0.png, file_pg_1.png, etc.

convert file.pdf file_pg_%d.png

Additional options:

  • You can replace an alpha background with a white background using the parameters -background white and -alpha remove. See example below.
    convert -background white -alpha remove file.pdf file.png
  • You can change the density of an image (i.e. specify the dots per inch value) using the -density parameter. See example below.
    convert -density 300 file.pdf file.png

Want to learn more about ImageMagick? Check out their site here.

Advertisements

How to create symbolic links

Occasionally you will need to make a link to a file or directory in Linux. To create a symbolic link you will need to use the ln command, which will follow the form of;

ln -s <target> <link name>

Example: Assume you frequently use gnome-calculator and decide you want a link on your desktop so you can quickly start that application in the future. To accomplish this with a symbolic link you could do the following;

ln -s /usr/bin/gnome-calculator ~/Desktop/calculator

You can also update an old symbolic link by overwriting the link using the following command.

ln -sf /usr/bin/gnome-calculator ~/Desktop/calculator

or when linking to directories you will need to include an n option

ln -sfn /mydir/ linkname

Quick Tip: Local Port Forwarding

Recently I needed to learn how to access a http resource from work from my home computer. Being relatively new to ssh, I was completely unaware I could forward a port and access the required resource form my home computer.

If you can ssh into your work server, you can perform local port forwarding using the following ssh command.

Syntax:

ssh <username>@<hostname> -L <localport>:<host>:<hostport>

Example:

ssh myusername@mypretendworkserver.com -L 8080:localhost:8057

The above example, forwards localhost:8057 from my work server’s to my home computer’s localhost:8080, giving me local access to a resource previously not accessible.

To learn more about local and remote port forwarding check out this website.

Quick-Tip – Netstat: Processes and Port Numbers

Earlier today I needed to kill a process that was occupying a specific port of a network. After a quick search online I learned from a website that Netstat can list listening sockets and provide the program PID’s which are using a specific port. The command to do this is as follows;

netstat -lp

This approach can be further refined if you know which port to look for, by piping a grep command afterwards with a specified port number;

netstat -lp | grep <port #>