##### Page tree
Go to start of banner

# An Introduction to Research Computing at York

You are viewing an old version of this page. View the current version.

Version 116

This course has been designed to help users access the research/teaching and Viking Linux servers. The aim is to provide you with some basic Linux commands to get you going.  You can access these machines using Windows, Mac or Linux.

# Introduction

There are a number of different computing facilities available at the University of York.  Have you found any of the following when doing research on your own computer?

• It uses all your machine's resources (compute cores or memory)

• You need lots of memory

• You need GPUs

• You are either using or producing a lot of data

• You think you could cut your job into smaller chunks and process them at the same time
• You know you want to analyse larger datasets in the future.

We have a few different machines to use when you have these problems: individual large machines known as the research and teaching servers, and the Viking compute cluster, a connected group of hundreds of machines. Here we will give you a very brief introduction on how to access these machines.

# The research and teaching servers

These servers are also known as the Linux Managed Service or LMS for short. There are currently four research servers (research0, research1, research2 and research3) and two teaching servers (teaching0 and teaching1). Detailed information on the server specifications can be found here.  These machines are Desktops, similar to what you may have at home or in your office, but with a large number of compute cores and memory.  This means that work that your local machine is struggling with may easily be run on one of these machines. You can log on to these machines from anywhere on campus, or off campus if you use the Virtual Private Network (VPN) or SSH gateway service. Some caveats:

• They are a shared machine which means a number of users may be logged on at the same time
• They run Linux so you need a little bit of Linux command line knowledge to get started
• They get rebooted on the first Tuesday of every month, so any jobs running then will be killed

## Exercise 1 - Logging into the research or teaching servers.

There are different ways to login to the LMS depending on what operating system you are running.  We will break down the different options here.

### Accessing research and teaching servers off campus

To access the research and teaching servers off campus you can either use the Virtual Private Network - VPN or the SSH gateway service (registration required). The instructions below should work if you log on through the VPN; the SSH service works slightly differently.

### Access from a Windows desktop

#### Command-line access using PuTTY

PuTTY is available on all IT Services Managed Windows systems. It is pre-installed on Classroom PCs; on Office PCs you can install it from Run Advertised Programs / Software Center. It appears under "Internet Tools" on the start menu.

When you run PuTTY for the first time, enter the following settings to log on to the research0 server (or replace research0 with teaching0, research1 etc):

1. Add the name "research0.york.ac.uk" to the 'Host Name' field
2. Check the 'Connection Type' to SSH
3. Type the name "research0"  in 'Saved Sessions'
4. Click 'Save'

1. Expand the 'SSH' tab from the 'Connection' list in the 'Category' box
2. Choose 'X11' from 'SSH' list
3. Check 'Enable X11 Forwarding'

1. Choose 'Session' from the 'Category' box
2. Click 'Save'

##### Connecting to research0
1. Start PuTTY
2. Select 'research0' from the 'Saved Sessions'
3. Click 'Open'
4. The first time you connect you will get a security alert showing the fingerprint of the server, labeled as 'ssh-rsa' or 'ssh-ed25519'. Check the fingerprint below for the label shown and click "Yes" to proceed if it matches.

```ssh-ed25519 255 SHA256:J4Bqti3rhC4qhnU0YLPX7jScNOlm+rXcHUBzl9AMqNE research0
ssh-ed25519 255 SHA256:lRu6KP3DviVUg1fxr39b1bzCRv5lsIlZrORA6qjVRTM research1
ssh-ed25519 255 SHA256:nOrLWS02W5Dk8SsspFutMd/z1Jh2mq7rzo27vyYwl4w research3
ssh-ed25519 255 SHA256:lpdXExChAcX3xaEkknD8YBIGz1cQaFKQmAcJ710DYaI teaching1

ssh-rsa 2048 5c:43:e5:e6:57:e0:4d:9f:f8:b5:ca:52:2f:30:39:ef research0
ssh-rsa 2048 bb:1f:6e:58:fa:d7:23:0d:ae:b2:b2:e8:62:a0:e7:5c research1
ssh-rsa 2048 99:da:16:61:09:e0:19:1f:53:0e:2b:e9:2a:22:50:99 research3
ssh-rsa 2048 ac:7e:1e:2a:05:d8:a1:3b:cf:b5:77:48:d0:bb:8a:22 teaching0

ssh-ed25519 5a:c9:c1:76:16:00:42:45:f9:e5:bd:63:5d:87:db:8a research0
ssh-ed25519 f4:51:59:b7:b5:74:1c:14:a7:2c:78:1c:11:1f:72:cc research1
ssh-ed25519 76:93:b3:2d:e0:73:cb:25:a5:9e:c7:bd:ce:76:8f:a2 research2
ssh-ed25519 64:b2:f0:11:93:fc:d7:ea:12:bb:90:bc:7d:06:75:cc research3
ssh-ed25519 f4:ff:10:59:1e:5f:21:10:14:59:6e:04:16:63:7d:95 teaching0
ssh-ed25519 bc:73:f8:4f:40:7a:6b:41:73:90:f6:77:2b:4f:aa:d5 teaching1```

The previous methods using NX Client and eXceed are now deprecated.
x2go client is available on all IT Services Managed Windows systems. It is pre-installed on Classroom PCs; users on Office PCs can install it from Run Advertised Programs / Software Center. It appears under "Internet Tools" on the Start Menu and there are pre-defined menu entries for research0 and teaching0.

On unmanaged PCs you can download the installer from the x2go Website. You will need to configure the settings as follows for research0 (or replace research0 with the name of the server you want to use):

1. If the "New session" panel does not appear, select the menu item "Session | New session..."
2. Enter "research0" in the 'Session name' field at the top
3. Enter "research0.york.ac.uk" to the 'Server: Host:' field
4. Change the 'Session Type' to XFCE
5. Click "OK" (all other settings can stay on default).

If you wish to change any settings:

2. Click the pull-down on the corner of the panel and select "Session preferences..."

### Access from a Mac

Go to the Finder on your Mac, find Applications, open the Utilities folder in Applications and then start the Terminal app from the Utilities folder. (You may wish to add Terminal to your Dock.) Then type the following, using your university username (abc123) instead ofusername. You don't need to type the $; this is an example of a prompt, which tells us the terminal is ready for us to type something. You should see something similar when you open Terminal, though it may be a bit longer (it may show your username for example). Just type anything from after the$.

Logging into research0

$ssh username@research0.york.ac.uk For a graphical login, install and configure the x2go client software as described in the unmanaged Windows section above. teaching0 and the other servers can be accessed in the same manner. ### Access from a UNIX server or desktop To login from a terminal window, type the following from your local machine with your university username (abc123): Logging into research0$ ssh username@research0.york.ac.uk

If you require X forwarding, type:

Logging research0 with X forwarding

$ssh -X username@research0.york.ac.uk You will be prompted for your IT Services password. Accessing teaching0 is done in the same manner. # Using the research/teaching servers with the Linux command line interface Once you have successfully logged into the research or teaching servers, they may look very different to what you are used to, particularly if you are used to using Windows. Please do not let this put you off. The research computing team have successfully managed to help many people use these computers who have never used the Linux command line before. It takes a bit of getting used to but the more you use it the easier and quicker it will become over time. The command line, or shell, has been the major interface for the Unix/Linux operating system since it was first conceived in the late 1960s. The shell allows interaction with the operating system through a text based interface, rather than the graphical interface you are used to. While the graphical interface is easy to learn, and usually makes simple things easy to do, it can be hard to do complex things like operate on large numbers of files, or make different tools work together. The shell can be hard to learn, but is much more powerful and flexible than most graphical interfaces, so can be very useful for research, where we often want to try new things on large data sets. In this tutorial, we will only scratch the surface of the shell's features, just to get you started, but we will note some further features at the end of the tutorial that you may want to look into. The user starts the shell by logging into the computer with a userid and password: Logging in ```****************************************************************************** *** THE UNIVERSITY OF YORK IT SERVICES *** *** *** *** THIS IS A PRIVATE COMPUTER *** *** UNAUTHORISED ACCESS STRICTLY PROHIBITED *** ****************************************************************************** login: user001 password: Last login: Mon Sep 8 14:12:44 2014 from gallifrey.york.ac.uk -bash-4.1$

```

The last line is a command prompt and it is the means by which the computer is telling you that it is ready to accept a command from you. If you do not see the prompt, the computer is probability still executing the last command you have typed. The user types commands which take the form:

program [ options ] [ arguments ]

Roughly speaking, program is the name of the program we want to run, arguments are objects we want to process (typically data files or folders), and options modify how the program will run. Options to a command are usually proceeded by a '-' or '- -' to differentiate them from arguments. The following exercise demonstrates using the echo program with a series of arguments and the ls program with or without options.

## Exercise 2 - Running commands in the Linux shell

When you see the prompt type the following command (you can also copy and paste the command into your terminal).

`echo I love York`

What happens?  The terminal should write out "I love York".  echo is a small program that takes a series of arguments and repeats them to the user.

Now try typing the following commands.

```ls
ls -l```

What do you see? Something like this?

Example of command execution
```-bash-4.1$ls bin Chemistry Desktop examples Experiments intel jobs logs tmp -bash-4.1$ ls -l
total 296
drwxr-xr-x 2 abs4 csrv        4096 Jun 24 09:39 bin
drwxr-xr-x 3 abs4 csrv        4096 Jun  6 09:23 Chemistry
drwxr-sr-x 2 abs4 elecclust   4096 Mar 11 10:53 Desktop
drwxr-xr-x 3 abs4 csrv        4096 Jun 30 12:21 examples
drwxr-xr-x 5 abs4 csrv        4096 May 23 11:34 Experiments
drwxr-xr-x 3 abs4 csrv        4096 Aug 14 12:26 intel
drwxr-sr-x 3 abs4 elecclust   4096 Aug 15 12:49 jobs
drwxr-xr-x 2 abs4 csrv      266240 Aug 15 13:48 logs
drwxr-xr-x 3 abs4 csrv        4096 Aug 14 14:50 tmp
-bash-4.1$``` The ls command lists all of the files in your current directory. A directory is equivalent to a folder. The ls -l command gives you a long list, showing more information about each file or folder such as who is the owner of the file, who can access it, when it was last accessed. You can use most Linux programs in a number of ways by adding extra options. Here for ls -l we added the -l option. If you need to know more about a program you can use either of the following: ```ls --help man ls``` ls can also take arguments as input. For example, to see the contents of a directory in your current directory, pass the name of the directory to ls as an argument. You can combine options and arguments, like the second command below: ```ls Desktop ls -l Desktop``` ### Filesystem organisation The file system is the component of the operating system that organises data into files. These files are organised into directories (just like directories in Windows Explorer or the Mac Finder). When you have logged in you will be placed in a directory which is called your home directory. To find the name of the directory use the program pwd (print working directory). Now try running the following commands. Here we have shown the prompt (-bash-4.1$) followed by the command to type on one line, then the output of the command on the following line (e.g after the -bash-4.1$, the first command is pwd, and the output is /home/userfs/e/ejb573; do not type the prompt as well, only the command). Your output will be slightly different as it will display the path to your home directory. Locating your home directory and files ```-bash-4.1$ pwd
/home/userfs/e/ejb573
-bash-4.1$cd /home -bash-4.1$ pwd
/home
-bash-4.1$cd -bash-4.1$ pwd
/home/userfs/e/ejb573
-bash-4.1$cd .. -bash-4.1$ pwd
/home/userfs/e
-bash-4.1$cd -bash-4.1$ pwd
/home/userfs/e/ejb573
-bash-4.1$``` The output of the pwd command, /home/userfs/e/ejb573, is called a pathname, and this specifies the location of user ejb573's home directory. The first '/' in the pathname is called the root directory, the top-level directory in the hierarchy. Names following the '/' are directory names. Directories within directories are called sub-directories. Path names can also specify the location of files. The last part of a pathname (after the last /) is typically the name of a file or directory. The cd program lets you change your working directory to another directory in the file system. cd with no arguments places you back in your home directory. The special argument '..' means the directory above your current directory (known as the parent directory). ### Creating, moving and copying files and directories You can create new files with the touch program and new directories with mkdir. You can move or copy files or directories to other locations with the mv (move) and cp (copy) programs. First, let's create a new file and directory. Create a new directory ```-bash-4.1$ touch afile
-bash-4.1$touch bfile -bash-4.1$ mkdir new-dir
-bash-4.1$ls afile bfile Chemistry examples intel logs tmp bin Desktop Experiments jobs new-dir ``` You should now see the files afile and bfile and the directory new-dir. Let's experiment with afile and new-dir: Create a new directory ```-bash-4.1$ ls
afile  bin        Desktop   Experiments  jobs  new-dir
bfile  Chemistry  examples  intel        logs  tmp
-bash-4.1$mv afile new-dir -bash-4.1$ cp bfile new-dir
-bash-4.1$ls bfile Chemistry examples intel logs tmp bin Desktop Experiments jobs new-dir -bash-4.1$ ls new-dir
afile  bfile
-bash-4.1$mv new-dir/afile . -bash-4.1$ ls
afile  bin        Desktop   Experiments  jobs  new-dir
bfile  Chemistry  examples  intel        logs  tmp
-bash-4.1$``` This example creates a new directory, 'new-dir', We then move the file 'afile' to it and create a copy of 'bfile'. We then move the file 'afile' back to our current working directory. The '.' argument in "mv new-dir/afile ." means the current working directory, so this command moves 'afile' to your working directory. Copying a directory is a little more complicated as the directory may contain files and directories. We use cp's '-r' option (recursive) to do this. Copying a directory ```-bash-4.1$ ls
afile  bin        Desktop   Experiments  jobs  tmp
bfile  Chemistry  examples  intel        logs
-bash-4.1$ls tmp icc-start ifort-start logs mpi-stop start test icc-stop ifort-stop mpi-start new-dir stop -bash-4.1$ cp tmp/test .
cp: omitting directory `tmp/test'
-bash-4.1$cp -r tmp/test . -bash-4.1$ ls
afile  bin        Desktop   Experiments  jobs  test
bfile  Chemistry  examples  intel        logs  tmp
-bash-4.1$ls test test.c test.cpp test.f test.f90 test.x -bash-4.1$

```

In this example we wish to copy the contents of the directory 'tmp/test' into the current directory. cp will not copy a directory; we have to use the '-r' (recursive) option to tell cp to copy all files and directories within the directory.

### Deleting files and directories

You can use the rm (remove) program is used to delete files. Please be careful with these commands, because Linux has no undo!

`rm filename`

To remove a directory and all of its contents use the rm -r (recursive) option to the rm command. To be safe and check the files before you remove them use -ri (recursive and interactive) options.

`rm -ri dirname`

# Displaying and editing the contents of files

There are a variety of different tools to help you display and edit the contents of your files.  We will provide some examples below but you may find other ones which you prefer to use in the future.

## Exercise 3 - Displaying the contents of files

File contents can be displayed with several different Linux programs. cat (concatenate files) will print your file to the screen, but this is not a good idea when the files are large. Instead, we can use less to view the file one screen at a time. Try them both on an existing file on the research/teaching servers (here we are using a file we already have called snark2).

cat and more
``` -bash-4.1$cat snark2 The Hunting of the Snark By Lewis Carroll Fit the First The Landing "Just the place for a Snark!" the Bellman cried, As he landed his crew with care; Supporting each man on the top of the tide By a finger entwined in his hair. "Just the place for a Snark! I have said it twice: That alone should encourage the crew. Just the place for a Snark! I have said it thrice: What I tell you three times is true." -bash-4.1$ less snark
The Hunting of the Snark
By Lewis Carroll
Fit the First
The Landing
"Just the place for a Snark!" the Bellman cried,
As he landed his crew with care;
Supporting each man on the top of the tide
By a finger entwined in his hair.
"Just the place for a Snark! I have said it twice:
That alone should encourage the crew.
Just the place for a Snark! I have said it thrice:
What I tell you three times is true."
The crew was complete: it included a Boots—
A maker of Bonnets and Hoods—
A Barrister, brought to arrange their disputes—
And a Broker, to value their goods.
A Billiard-marker, whose skill was immense,

```

To move through the file with less, or to quit back to the command line, use the following keys:

• SPACE - display the next screen of text
• q - quit displaying the file
• b - skip backwards through he file
• /pattern - search for text in the file

There are many text editors available on Linux. The easiest to use is probably nano:

```nano filename
```

To edit text within nano, just type; to move around the file, use the arrow keys; to exit nano, type Control+X (^X is shown in the shortcuts at the bottom of the screen); to save the file, type Control+O (^O) and hit Enter when prompted for a filename. You might explore the other shortcuts shown at the bottom to try out some other features.

You might also try vi or emacs, which are harder to learn and use but very powerful once you get used to them. If you are using X forwarding (see above), you might also try gedit, which is a graphical text editor.

# Copying files and directories remotely

You may need to copy files from your machine at home to one of the research/teaching servers.  There are a number of ways to do this.

## Exercise 4 - Copying files from your machine to the research machines

There are different exercises on copying files dependent on what operating system you use on your local machine.

### Copying Files To/From a Windows Desktop

WinSCP is an open source free SFTP client, SCP client, FTPS client and FTP client for Windows. Its main function is file transfer between a local and a remote computer. WinSCP is available on IT Services supported desktops or can be downloaded from http://winscp.net/eng/index.php.

Run WinSCP  from the Start menu or double clicking on the icon on the desktop;

#### Running WinSCP

You can click the "Save" button to save the session details for future use:

The file manager window will be displayed:

The drag-and-drop interface is a similar to Windows file manager and its use should be intuitive.

### Copying Files To/From a Linux/MacOS desktop

There are a number of ways to copying files and directories using Linux command line.

you can copy your data from any Linux device to Viking using the following commands

• scp
• rsync

Here are a couple of examples.

#### scp

This is recommended for a small number of files.

You wish to copy your data from local machine to your home area on the research machines.  Run the following commands on your local machine in the terminal.

```-bash-4.1$touch cfile -bash-4.1$ touch dfile
-bash-4.1$mkdir new-dir2 -bash-4.1$ mv dfile new-dir2
-bash-4.1$ls cfile Chemistry examples intel logs tmp bin Desktop Experiments jobs new-dir2 ``` Here we have created some test files and directories on your local machine. We will now copy these to your home directory on research0. You will need to enter your University of York password and replace abc123 with your University of York username. ```-bash-4.1$ #For an individual file
-bash-4.1$scp cfile abc123@research0.york.ac.uk:~/ -bash-4.1$ #For a folder with lots of files
-bash-4.1$scp -r new-dir2 abc123@research0.york.ac.uk:~/ ``` Now login to research0 you should now see the following files and folders in your home area. ```-bash-4.1$ ls
cfile new-dir2
```

The scp command securely copies these files and folders to the research machine.  The -r flag means scp will recursively copy everything within the folder new-dir2.  The :~/ at the end of the command is the location of where to send the files on the research machine.  In this case it is your home directory. If we wanted to send a copy of dfile directly to new-dir2 folder use the following command.

```-bash-4.1$#For an individual file -bash-4.1$ scp dfile abc123@research0.york.ac.uk:~/new-dir2/```

This can save you an extra step of moving files on the research machines. Note there was already a copy of dfile in new-dir2 on research0 - we copied it there when we uploaded new-dir2. scp will silently write over any existing file without warning you, so be very careful.

What if you want to copy files from research0 to your local machine?  Run the following commands on your local machine.

```-bash-4.1$#For an individual file -bash-4.1$ scp abc123@research0.york.ac.uk:~/cfile .

-bash-4.1$#For a folder with lots of files -bash-4.1$ scp -r abc123@research0.york.ac.uk:~/new-dir2 .
-bash-4.1$ls ``` After running ls, do you see the files on your local machine? There are many options you can use with scp. To view these options either run `man scp ` on the device you are using scp on or have a look at this scp wiki page. #### RSYNC Rsync is another command that will let you copy files and folders to the research machines. If you have a large number of files it is always best to use Rsync. The Rsync command will compare the files on your computer to the files already on the server, so if the network is interrupted you can run the command again and it will pick up where you left off. It will only copy files that do not exist on the other server or files that have been changed on your computer. To copy a folder new-dir2 from your local machine to your home directory on research0, run the following command on your local machine. `rsync -avz new-dir2 abc123@research0.york.ac.uk:~/` The flags on rsync mean different things. This would recursively transfer all files from the directory new-dir2 on your local machine onto the home directory on the research machine. The files are transferred in "archive" mode, which ensures that information about the files such as timestamps and permissions are preserved in the transfer. Additionally, the files will be compressed during the transfer so the transfer will be faster. There are many options you can use with rsync. To view these options either run `man rsync ` on the device you are using rsync on or consult the rsync webpage. # Finding and running programs on the research/teaching machines There are many programs available on the research/teaching machines. Some programs can be used all the time (like ls, scp and rsync). Some programs need to be loaded using the module system. In this next section we will try both options and show you the best way to find the program you need for your teaching or research. If you find the software you need is not installed, please email itsupport@york.ac.uk and we will aim to install the software for you. ## Exercise 5 - Running applications on the research/teaching machines. ### Running applications on the command line. You will need to login to the research machines with X forwarding enabled. If you followed the steps in Exercise 1 you will have already set this up. From linux or MacOS ssh with the -X flag `ssh -X abc123@research0.york.ac.uk:~/` Once logged in (either with putty or ssh) type matlab on the command line and wait for the gui to pop up. `matlab` There are a number of programs installed this way. If you have ever used linux on the classroom PCs all the programs available there are also available here. # Working with modules Modules allow us to support many permutations of application versions, built with different compiler versions and technologies. We can thus support new application versions, or optimised builds, without disruption to users who still require earlier editions. There are many programs installed for use on these machines. To see what programs are available type 'module avail' in the terminal. Do you see a list of available software? ```ejb573@research0:~$ module avail
--------------------- /usr/lib/Modules/3.2.10/modulefiles ----------------------
dot         module-git  module-info modules     null        use.own
----------------------- /usr/lib/Modules/uoymodulefiles ------------------------
its-hdd      its-net      Ubuntu/16.04 Ubuntu/18.04
--------------- /opt/york/phys/pkg/Modules/modulefiles/compilers ---------------
clang/3.8.0(default)  gcc/5.4.0(default)    gcc/7.4.0
clang/4.0.0           gcc/7                 intel/17.0.0(default)
gcc/4.8.3             gcc/7.1.0             miniconda/3.7
gcc/4.9.0             gcc/7.3.0             Tcl/8.6.1
------------------ /opt/york/phys/pkg/Modules/modulefiles/mpi ------------------
mpich/3.2      mpich2/1.5     openmpi/1.10.7 openmpi/2.1.1
--------------- /opt/york/phys/pkg/Modules/modulefiles/libraries ---------------
cube/4.3.5           otf2/2.0             slepc/3.6.3
CUDA/10.1.160        petsc/3.4.5          slepc/3.7.4
CUDA/7.5.18          petsc/3.5.4          slepc/3.9.1
CUDA/8.0.61.p02      petsc/3.6.4          slepc-complex/3.11.2
fftw/3.3.6(default)  petsc/3.7.6          slepc-complex/3.5.4
fftw/3.3.8           petsc/3.8.4          slepc-complex/3.7.4
ghost/1.0            petsc/3.9.0          spglib/1.10.4
hdf5/1.8.16          petsc-complex/3.11.4 spglib/1.9.10
hdf5/1.8.18          petsc-complex/3.5.4  sundials/2.7.0
lapack/3.7.0         petsc-complex/3.7.7  szip/2.1.1
lz4/1.9.1            scalasca/2.3.1       Tk/8.6.1
MESASDK/22Aug2018    scorep/3.1           uda/1.0.0
netcdf/4.4.1.1       slepc/3.4.4          zlib/1.2.11
opari2/2.0.2         slepc/3.5.4
```

If you need to search for an application run module avail application-name on command line.  How many versions of python are there available on the research/teaching machines?

```ejb573@research0:~$module avail python ------------------------- /opt/yarcc/Modules/compilers ------------------------- python/2.7.11 python/3.4.0 python/3.6.0 python/3.6.5-bm python/2.7.14 python/3.5.1 python/3.6.4 python/2.7.6 python/3.5.3 python/3.6.5 ``` There are 12 versions available using the module command. Now let us load a module. On the command line run the following command ```ejb573@research0:~$ python --version
Python 2.7.17
```

The default, system version Python version is 2.7.17.  We actually want a newer version of python to run our code.  Let us load a new version of Python with the module system

```ejb573@research0:~$module load python/3.6.5 ejb573@research0:~$ python --version
Python 3.6.5
```

We have now loaded a new version of python.  To check this you ran python --version.  You can also use module add python/3.6.5 to add a module.

To remove the module run

```ejb573@research0:~$module unload python/3.6.5 ejb573@research0:~$ python --version
Python 2.7.17
```

# Extra Information

This has been a very basic introduction to the command line, just to get you started. You may also want to look up the following features:

• Using pipes (|) to pass the output of one tool as input to the next, allowing you to make new tools by combining existing ones
• Redirecting input and output to files with >
• Using wildcard characters such as * to refer to many files or directories at once
• Writing scripts: saving a series of commands to a text file and then running the file as a program
• Running jobs in the background with &, nohup and nice
• Variables and options for environment customisation
• Command-line editing

If you wish to learn more about how to use Linux command line there are a number of online resources.  We do recommend The Unix Shell - Software Carpentry, where all the exercises and answers are available online. We also have our Online training resources page which provides various options depending on where you wish to get started.

# What shall I do if I need more computational power?

## The Viking Cluster

If you are finding that your code is still taking a long time to finish or you wish to scale your work, the Viking cluster may be what you need.

Viking is a large Linux compute cluster aimed at users who require a platform for development and the execution of small or large compute jobs.

See our Viking Quick Start Guide to get started.  There will also be a similar online course 'introduction to Viking' available by November 2021.

### What is a cluster?

A cluster consists of many (hundreds or thousands) rack mounted computers called nodes. It would be similar to having hundreds of desktop computers sitting in the same room and able to talk to each other.  Clusters are often accessed via login nodes, which can send jobs to the other nodes in the cluster. Your commands will not be run immediately, but will be sent to a queue, and run when there is space on the cluster to run them.

The Viking cluster is Linux based and can be accessed in a similar manner to the research servers, but instead of accessing, say, research0.york.ac.uk, you would access viking.york.ac.uk. We have extensive wiki pages on how to get started on Viking. Please see here for further details and if you ever need help email itsupport@york.ac.uk where one the research computing team can assist you.

Viking is a multidisciplinary facility, supporting a broad spectrum of research needs, free at the point of use to all University of York researchers. Viking is as much a facility for learning and exploring possibilities as it is a facility for running well-established high-performance computing workloads. In this light, we encourage users from all Faculties, backgrounds and levels of ability to consider Viking when thinking about how computing might support their research.

To access Viking you need a user account, and your user account needs to be associated with a project code. Project codes are typically given to research groups; ask your PI for their code, and if they don't have one, ask them to fill in the Project Application Form. Once you have a project code, you can apply for a user account by filling in the User Application Form. It can take 24 hrs for new accounts to be processed. The Viking Wiki has more help on How to access Viking.

• No labels