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Server login

Learning outcomes

Note

You might already be able to do some or all of these learning outcomes. If so, you can go through the corresponding exercises quickly. The general aim of this chapter is to work comfortably on a remote server by using the command line.

After having completed this chapter you will be able to:

  • Use the command line to:
    • Make a directory
    • Change file permissions to ‘executable’
    • Run a bash script
    • Pipe data from and to a file or other executable
  • Program a loop in bash

Choose your platform

In this part we will show you how to access the cloud server, or setup your computer to do the exercises with conda or with Docker.

If you are doing the course with a teacher, you will have to login to the remote server. Therefore choose:

  • Cloud notebook

If you are doing this course independently (i.e. without a teacher) choose either:

  • conda
  • Docker

Exercises

First login

If you are participating in this course with a teacher, you have received a link and a password. Copy-paste the link (including the port, e.g.: http://12.345.678.91:10002) in your browser. This should result in the following page:

Info

The link gives you access to a web version of Visual Studio Code. This is a powerful code editor that you can also use as a local application on your computer.

Type in the password that was provided to you by the teacher. Now let’s open the terminal. You can do that with ++ctrl+grave++. Or by clicking Application menu > Terminal > New Terminal:

For a.o. efficiency and reproducibility it makes sense to execute your commands from a script. With use of the ‘new file’ button:

Material

Exercises

First login

Docker can be used to run an entire isolated environment in a container. This means that we can run the software with all its dependencies required for this course locally in your computer. Independent of your operating system.

In the video below there’s a tutorial on how to set up a docker container for this course. Note that you will need administrator rights, and that if you are using Windows, you need the latest version of Windows 10.

The command to run the environment required for this course looks like this (in a terminal):

Modify the script

Modify the path after -v to the working directory on your computer before running it.

docker run \
--rm \
-p 8443:8443 \
-e PUID=1000 \
-e PGID=1000 \
-e DEFAULT_WORKSPACE=/config/project \
-v $PWD:/config/project \
geertvangeest/ngs-longreads-vscode:latest

If this command has run successfully, navigate in your browser to http://localhost:8443.

The option -v mounts a local directory in your computer to the directory /config/project in the docker container. In that way, you have files available both in the container and on your computer. Use this directory on your computer to e.g. visualise data with IGV. Change the first path to a path on your computer that you want to use as a working directory.

Don’t mount directly in the home dir

Don’t directly mount your local directory to the home directory (/root). This will lead to unexpected behaviour.

The part geertvangeest/ngs-longreads-vscode:latest is the image we are going to load into the container. The image contains all the information about software and dependencies needed for this course. When you run this command for the first time it will download the image. Once it’s on your computer, it will start immediately.

A UNIX command line interface (CLI) refresher

Most bioinformatics software are UNIX based and are executed through the CLI. When working with NGS data, it is therefore convenient to improve your knowledge on UNIX. For this course, we need basic understanding of UNIX CLI, so here are some exercises to refresh your memory.

If you need some reminders of the commands, here’s a link to a UNIX command line cheat sheet:

UNIX cheat sheet

Make a new directory

Make a directory scripts within ~/project and make it your current directory.

Answer 
cd ~/project
mkdir scripts
cd scripts

File permissions

Generate an empty script in your newly made directory ~/project/scripts like this:

touch new_script.sh

Add a command to this script that writes “SIB courses are great!” (or something you can better relate to.. 😉) to stdout, and try to run it.

Answer

Generate a script as described above. The script should look like this:

#!/usr/bin/env bash

echo "SIB courses are great!"

Usually, you can run it like this:

./new_script.sh

But there’s an error:

bash: ./new_script.sh: Permission denied

Why is there an error?

Hint

Use ls -lh new_script.sh to check the permissions.

Answer 
ls -lh new_script.sh

gives:

-rw-r--r--  1 user  group    51B Nov 11 16:21 new_script.sh

There’s no x in the permissions string. You should change at least the permissions of the user.

Make the script executable for yourself, and run it.

Answer

Change permissions:

chmod u+x new_script.sh

ls -lh new_script.sh now gives:

-rwxr--r--  1 user  group    51B Nov 11 16:21 new_script.sh

So it should be executable:

./new_script.sh

More on chmod and file permissions here.

Redirection: > and |

In the root directory (go there like this: cd /) there are a range of system directories and files. Write the names of all directories and files to a file called system_dirs.txt in your working directory.

Answer 
ls / > ~/project/system_dirs.txt

The command wc -l counts the number of lines, and can read from stdin. Make a one-liner with a pipe | symbol to find out how many system directories and files there are.

Answer 
ls / | wc -l

Variables

Store system_dirs.txt as variable (like this: VAR=variable), and use wc -l on that variable to count the number of lines in the file.

Answer 
FILE=~/project/system_dirs.txt
wc -l $FILE

shell scripts

Make a shell script that automatically counts the number of system directories and files.

Answer

Make a script called e.g. current_system_dirs.sh: 

#!/usr/bin/env bash
cd /
ls | wc -l