General Center Questions

NCF Cluster Questions

  Getting Started

  SLURM Topics: How to use the compute cluster

  Basic UNIX Topics

  Advanced Topics

  NCF Troubleshooting

CBSCentral Questions

Quality Control


  Quantitative QC: Extended BOLD QC via CBSCentral

  Qualitative QC: Looking at your data

  Preventive QC: at the scanner

Matlab Questions

Scanner Questions

        Getting Started

      Interactions with your Experiment

       SMS/Multiband topics

      Operating the Scanner

        Scanner Troubleshooting

Basic MRI Physics and Protocol Questions

       Analysis tips

What should I acknowledge or cite when writing up my work?

ALL published work resulting from research studies fully or partially undertaken at the Center for Brain Science must include formal acknowledgement, using the standardized language below, of support from the Harvard Center for Brain Science. If the research involves data collected on the Prisma MRI scanner, the NIH Shared Instrumentation Grant must also be acknowledged.
Acknowledgements should also be included on any posters or presentations.

Please use the following language when acknowledging the Center and the NIH instrumentation grant in all publications.

“This research was carried out in whole or in part at the Harvard Center for Brain Science. This work involved the use of instrumentation supported by the NIH Shared Instrumentation Grant Program; specifically, grant number S10OD020039.”

If you used the SMS/multiband sequences, you should also cite them. Instructions for this can be found here.

How can I get help?

For assistance with NCF related issues contact: rchelp [at] fas [dot] harvard [dot] edu or call (617) 299-9724 and leave a message. Please provide as much detail as possible so that the Helpdesk staff can address your problem quickly. In addition, RC has office hours weekly at 38 Oxford St., behind the Northwest building.

Questions about network, desktop or laptop support should be directed to Harvard University IT support (HUIT) at ithelp [at] harvard [dot] edu or (617) 495-7777.

For questions about CBSCentral (XNAT) or the NRG tools (i.e. fcfast) contact the neuroinfomatics group at at cbssupport [at] neuroinfo [dot] org. You can visit their page to find out more about what they do.

For questions about the scanning facility, including safety issues, contact Tammy at tmoran [at] fas [dot] harvard [dot] edu, and see here.

For questions about setting up scan parameters or MR physics questions, talk to Ross at rmair [at] fas [dot] harvard [dot] edu.

For questions about experimental paradigm design, data analysis issues, or comments/questions about anything on the FAQ page, contact Stephanie at smcmains [at] fas [dot] harvard [dot] edu.

What is the NCF?

The Neuroimaging Compute Facility (NCF) is a central enabling infrastructure for neuroimaging teaching and research whose mission is to provide high performance, high power, robust, reliable and secure computer systems and human expertise to meet the challenges of neuroimaging research and teaching. The NCF is a collaboration between the Center for Brain Science and the Life Sciences Division of Research Computing. It consists of a compute cluster with a vnc (ncfood) interface and several login nodes.

Who may use the NCF?

The NCF is a resource for the Harvard Neuroimaging Community and their collaborators. To access, just sign up for a user account indicating your laboratory and Principal Investigator.

How do I use the NCF?

There are several main uses for the NCF. With modern technology and advanced analysis techniques, datasets can be very large and can often fill up a users’ personal computer quickly. Therefore, the NCF provides a safe and secure location to store data. In addition, the data is backed up automatically and regularly, providing peace of mind.

Second, the NCF provides a compute cluster for running your data analysis on. This can be done in several ways, but mainly by logging in remotely to the cluster via a VNC session. This is where you can run graphical programs to look at your data, and where you can submit jobs to the cluster for number crunching. In addition, if you need both graphical abilities and number crunching abilities, you can use an interactive session.

How do I get an NCF User Account?

To request a new account, fill out the online Account Request form. If you select a PI that is for the NCF, the last page should say that NCF compute resource access has automatically been included. If for some reason it doesn't, please email RC (rchelp [at] fas [dot] harvard [dot] edu) and let them know.

If you are an outside user or just want access to the Spinal calendars, select Users without a Harvard Key (or with a key if you have one), Caroline West as your PI, and then select the Spinal calendars on the instrument tab.

You can also go to the second tab on that page, instruments, and request access to the Spinal calendars.

How do I set up my user environment/access software on the NCF?

If you are working in bash, which is the default on the NCF, you should have a file in your user directory called .bashrc. You can open/create this file using your favorite text editor, such as gedit. Copy and paste the lines from below.  This will get you all the default programs, including the NRG tools (fcfast, procfast), and many brain analysis packages.  Many of the defaults are very old versions, given that people often don't want these to be randomly changing on them.  To see how to select a different version, go here.

# writen by Luis Silva 02/10/2012
# For assistance please contact rchelp [at] fas [dot] harvard [dot] edu
# NCF Base setup install script #

#default environment, by using 'current' it will be updated automatcially with new releases.  This should not change the default versions of software without assuring backwards compatibility.

. /ncf/tools/current/code/bin/env_setup.sh

#this makes your history file larger and easier to read so RC can more easily help you

#This makes your command prompt pretty, including having the pathname to where you are


# Insert additional configuration below this line, like module loading and alis setting #


If you have questions about setting up your environment, you can contact Stephanie (smcmains [at] fas [dot] harvard [dot] edu) or RC help (rchelp [at] fas [dot] harvard [dot] edu). See below for how to change versions of software via modules.


How do I access the NCF network remotely (VPN)?

The latest Neuroimaging Compute Facility (NCF 2.0) uses two-factor authentication, which requires users to use their username and password as well as second factor, which is now (5/18/2012) an openauth token, in order to gain entry to NCF infrastructure. This is not the same two-factor authentication you have to do for the Harvard key system. Its also not the same vpn server, though you can use the same vpn app, just with a different address.

You must first install the openauth software.  The link below will provide instructions for how to install this on your smart phone and/or your computer. This software creates a token that is specific to you, so if you use a different computer, you will need to set it up again, or use the token from your phone.  Therefore, if you plan on VPNing to the cluster from multiple locations it is highly recommended to install the phone app also.  Just follow the instructions on the page below, until you get the java application installed, then continue on with these instructions to see how to VPN. Importantly, they provide two options for download, most likely you want the second one, which provides a more traditional application for you to download, with an icon for your desktop. The other one creates more of a file (JAuth.jar) that you need to run.


Once you download the software click on the JAuth.jar (or JAuth.app) file to launch the program.  This will make a little black and green box appear with a 6 digit code that is updated every minute or so. This code will be needed to successfully VPN to the NCF.

If you have a new Mac, you might get an error message telling you to download the Java Developer Kit. This means you will need to install java to get the program to run. This can be downloaded from here.

Now that you have the openauth token generator, you will need the actual VPN client. These steps will only need to be followed once per machine you want to install it on, and this application is not specific to a user, so if you find it already installed on a machine you can use it if you have your own personal openauth token. It is also the same one you use to VPN more generally to Harvard, you just need to change the address as listed below. To get the VPN client (if you don't already have it) go here. Again, you will only have to do this step once, as this will install the Cisco AnyConnect VPN Client onto your system.

The web based installation of the client almost always fails. However, after it fails, it gives you the option to download the disk-image. Go ahead and do that. When you try and open the installer package, it may give you an error that it is broken and can't run. This is usually due to your security preferences in your web browser.

On a mac:

  • Go to System Preferences -> Security & Privacy
  • Click on the General tab
  • Click on the lock to allow changes
  • Under the heading "Allow applications downloaded from:" chose Anywhere

Then double lick on the vpn.pkg and the installation should work. Afterwards, you can go back and set the "Allow applications downloaded from:" to be Mac App Store and identified developers.

Once you launch the VPN client, make sure the "Connect to" path name at the top is vpn.rc.fas.harvard.edu

If this isn't in the drop down menu, you will have to type it in. It should then be remembered for future sessions.

Next you will be prompted for your username: @ncf i.e. jsmith@ncf, DON'T FORGET THE @NCF!! Next you will be prompted for your password: The second password field is for the 6 digit passcode from your openauth app. Once you enter this information, you should be able to connect.

Occasionally, you may have to try logging in once or twice, particularly if the token is getting ready to expire right as you put it in. Once you are connected, you want to start a VNC session by following these directions.

How do I access the NCF - VNC - Open On-Demand remote desktop?

This partly depends on what you want to do. We have a VNC server, a remote desktop session that is great if you need graphics. You can also ssh directly to the cluster via ncflogin if you don't like the remote desktop option, or if it is full or down for any reason.

The biggest thing you can do to speed things up is GET A WIRED CONNECTION!!! The wireless network is much slower, and while convenient, is not great for remotely working with the cluster. We also now have the ability to take advantage of virtual GL which speeds up graphic intensive programs.

Also, please keep in mind the VNC remote desktop should be more for graphic intensive processes. If you need to do number crunching, make sure you are using the compute cluster, either by submitting your scripts, or if you still need graphics (like with matlab), you can run an interactive sessionfrom your VNC session.

Open On-demand Remote Desktop (VNC)

1. From Chrome (preferred) or Firefox while on the VPN, go to: https://ncfood.rc.fas.harvard.edu and login with your RC credentials.

Research Computing has written a nice FAQ on their website about this: https://www.rc.fas.harvard.edu/resources/documentation/ncf-vdi-apps/ This covers the interactive apps, including the remote desktop session, Jupyter notebook, and Rstudio. >/span>

For info on the other tabs available on the site see their FAQ, which was written for the general Odyssey cluster, though the general features are the same: https://www.rc.fas.harvard.edu/resources/documentation/virtual-desktop/. Scroll down to where it says: Quick Tour of the Dashboard.

Tips for using the interface

Graphics intensive programs: If you are running a graphics intensive program like Freeview or FSLeyes, or Workbench (this must be used with workbench for it to work!), you can vglrun before the name of the process:

vglrun freeview -v mysubj/mri/T1.mgz

Copy and Paste between local machine: This can be done via the clipboard, on the far right. To open it, click the little arrow on the left side of the desktop.

Then click on the image that looks like a clipboard. The window it opens is a place to copy and paste things back and forth, always with your laptops copy/paste commands. To get something from the cluster to show up there, highlight and middle click, or copy with your remote desktop copy commands.

Text editor: The default text editor is sublime, you will see it as an icon. To launch from the command line use:

subl name_of_file_to_open

How to make text look nicer: To make the text look a little 'smoother'. From within your remote desktop session, go to the top left corner to Applications ->Settings -> Appearance -> Fonts and change Hinting to None.

Edit keyboard shortcuts To change the command combinations for copy and paste: From within your remote desktop session, go to the top left corner to Applications ->Settings -> Appearance -> Settings and check Enable editable accelerators. Then go to a terminal window, click on Edit, and hover over Copy or Paste with your mouse. Then perform the key combination you would like to use. You should see the key combination listed on the right change. For reference, you can use ctrl-c for copy, and the system will smartly figure out when you want to copy something or kill a running process, for which the UNIX command is ctrl-c.

How do I access the NCF - ssh?

To ssh to the cluster, you must be on the VPN. You can then ssh to a login node. From a mac you can use Terminal. From a PC see here. This is a great place to submit scripts from, or edit files, but you shouldn't be doing any number crunching. Especially as the hardware differs fro the cluster, so if you do number crunching here and on the cluster the numbers could differ slightly.


ssh -YC ncfusername [at] ncflogin1 [dot] rc [dot] fas [dot] harvard [dot] edu


ssh -YC ncfusername [at] ncflogin [dot] rc [dot] fas [dot] harvard [dot] edu

p>This will put you on ncflogin5 through ncflogin8, which ever is least busy. You can also choose a specific one if you prefer.

How do I connect to the NCF from a PC?

The process is the same if you want to use the Open On-Demand remote desktop client. If you want to ssh to one of the login nodes like described here. To enable X11 forwarding in PuTTY you need to configure your settings.  

RC has some nice instructions here, see below for some basic steps.

Start up PuTTY.  In the configuration box you need to give it the Host Name of the vncserver. The hostname should be ncflogin.rc.fas.harvard.edu for centOS7, or ncflogin1.rc.fas.harvard.edu for centOS6. You can also save these settings by giving your session a name in the Saved Sessions box and then click Save.  You should save it again once you set the X11 forwarding.

Next, under the Connection Category, expand SSH (click where red arrow pointing) and choose X11.  Click on the Enable X11 Forwarding checkbox (where red arrow pointing).  

Then, click on the Session Category, and save your settings again.  Next time when you open this program, you can Load the saved settings.

Finally, click on Open.  You should then be prompted for your username and password.  When you are done, make sure you end your SSH session by typing exit at the command prompt before you X out of the PuTTY program.


What software is available on the NCF?

We use the lmod module system on the NCF. For some basic instructions from RC see here. If you don't see something you want, there are a couple of options for getting it. If you think it might be of use to others, you can email RC (rchelp [at] fas [dot] harvard [dot] edu) and ask for it. If you think others wouldn't be interested, you are always welcome to download software yourself. RC has a page on this, but keep in mind it was written for Odyssey. This page also has links for how to add packages to R and python. There are two main places software might be depending on who installed it.

Research Computing

To see a full list of their software, and which version of CentOS they work with, check out their software portal.


To see the NCF specific ones, you need to first load the ncf modules. This command should already be in your .bashrc. The name will indicate if it is CentOS7 compatible.

module load ncf

To see the modules available to us:

module avail ncf

This will show a list that looks something like:

To select a module, for instance, a newer freesurfer:

module load freesurfer/5.3.0-ncf

If there is a module missing that you would like, for instance a matlab version, just email RC (rchelp [at] fas [dot] harvard [dot] edu).

See the instructions below for setting SPM, as there is an additional step.

The old system will continue to work for awhile, and is described below. But please start transitioning to the new system.

Old system

Thanks to Tim O'Keefe from the Neuroinfomatics group, we have a simple script to change between most of the major brain analysis software packages.  If there is a version you want not listed below, contact Tim (timothy_okeefe [at] harvard [dot] edu) and CBS help (cbssupport [at] neuroinfo [dot] org) for support.

For the following 'loader' scripts to work, you must be using the default enviornment (see here). 

To get a list of availabe versions, type:


This should give you something that looks like the list below. Which has the software package name followed by the available versions.  To select one, type the command (load_??) followed by the version:

load_fsl 4.1.7


load_freesurfer 5.1.0

IMPORTANT: If you want this change to be permenant, you need to add it to your .bashrc file (located in your home directory).  Add it below the area saying "Insert additional configuration below this line".

Changing SPM is a little more compliated, because your matlab path must be updated.  See here.


load_afni: 2011_05_26_1457
load_caret: 5.0
load_dcmtk: 3.6
load_freesurfer: 4.0.2  4.5.0
load_fsl: 4.0.3  4.1.6  4.1.7
load_java: 1.5  1.5.0_22  1.6  1.6.0_21_64  1.6.0_24
load_matlab: 7.11  7.4  7.7  7.8  7.9
load_mricron: 2009_12
load_nit: 1.0  1.0.1  1.0.2  1.1  1.2  1.2.1  1.2.2  1.3.2  1.3.3  1.3.4  1.4  1.4.1  1.5.0b  dev
load_php: 5.3.10
load_python: 2.7.0  2.7.2
load_sd: 1.5.1
load_spm: 2.0  5.0  8.0  8.1  8.4667
load_xjview: 8.4


How much space will I be allocated to process and store my data?

Work and data storage space are allocated to the Principal Investigator of each laboratory. Within a lab, the PI is responsible for dividing up space, so see your PI for space requests. In addition, each user will have 20 GB of space in their home directory. Please do not use the home directory for data storage - it will run out fast!  And definitely don't run jobs from your home directory as it can slow everyone's account down.  In that case your account could be deactivated.

How do I set my permissions so that everything is readable and writable by my group?

Initially, your permissions on the cluster are set up so that new directories and files are readable and writable to you, and readable by your group, and by the world (in this case, everyone with access to our cluster). You can tell what the permissions of a file are by typing ls -l. You will see something like this:

For a file:

-rw-r--r-- 1 mcmains cnl 54 Oct 5 2012 file_name

For a directory:

drwxr-xr-x 1 mcmains cnl 54 Oct 5 2012 directory_name

For a script: -rwxr-xr-x 1 mcmains cnl 54 Oct 5 2012 script_name

The first slot is either - for a file or d for a directory. The next three slots designate the owner's permissions (r=readable, w=writable, x=executable). The next three are the permissions for the group, and the last three are everyone else. Following this is the user name of the owner (mcmains) and then the owner's group (cnl).

Often, you will share files with other people in your group. In this case, you might want other members of your group to be able to read and write (edit) your files. In addition, you may not want other's on the cluster to be able to read your files. The default permissions can be set by adding a line to your .bashrc file. What you add depends on the permissions you want.

The command is umask followed by three numbers that designate the permissions separately for the three designations (users, group, everyone else).

0=rwx   1=rw   3=r  7=nothing 

So if you wanted to make your files readable, writable, and executable by you and your group, but no one else, you would add the line:

umask 007

to your .bashrc file. For more information on permissions, including how to change them for just a single file or directory of files, see: https://en.wikipedia.org/wiki/Chmod

How do I get files back and forth between the NCF and my computer?

This can be done in two main ways, either via the command line or via a GUI. Both have two different ways depending on how much data you are trying to transfer.


1. Command line via rsync:

This command is great for a large amount of data or big files, as it is more of a sync than a copy. This means if the transfer gets interrupted for any reason, you can relaunch it and it will pick up where it left off. Launch this from a terminal window. RC has a page for this with more details. I will show a simple command below, since their instructions are for Odyssey.

rsync -av your_username [at] ncflogin [dot] rc [dot] fas [dot] harvard [dot] edu:directory_or_file_you_want_to_transfer .

You can also transfer to specific location on your computer by replacing the ending "." with a directory path.


2. Command line via sftp:


This is good for small to mid size files. If you have a large directory, or very large files you should use rsync. Start an sftp session from your laptop. To do this you will need to have a VPN session going, and a terminal window open:

sftp username [at] ncflogin [dot] rc [dot] fas [dot] harvard [dot] edu

You will be prompted for your password. It is important to note that it is easiest to start the sftp session from the directory that contains the files you want to put on the NCF or from the directory where you want files from the NCF to be placed, as the starting directory is the default directory and ‘tab completion’ doesn’t seem to work (at least not for me).

If you want to PUT files from your laptop to the NCF, go to the directory on the NCF where you want the files to end up and then type:

put <filename>

If you want to get files from the NCF, go to the directory where the files are (cd, ls, and most unix commands should work). Then:

get  <filename>

You can put or get multiple files using the * character to select multiple files.


3. GUI based via Open On-demand:

See the instructions on the Open On-demand, and go to the Files tab at the top. This is good for individual files that aren't too large.


3. GUI based via Filezilla:


You can also use a program to link the NCF to your computer so that you can surf through the directory structures easily on both, and just drag and drop files or folders that you want.  

There are a few free downloadable choices. Research computing has recently changed their recommendation from Cyberduck, to Filezilla. They have made nice instructions found here .  We strongly recommend using Filezilla, as it will be supported by RC going forward. You can follow their instructions, except when you specify the host. You want the host to be ncflogin.rc.fas.harvard.edu

How do I look at and/or edit a text file on the NCF or my laptop?

There are several ways to ‘read’ files on the cluster.

1. If you just want a quick view of the contents without opening up the file you can use ‘more’:

more <filename>

Press the space bar to advance the document, and ‘q’ to quit.

2. If you want to open the file up for editing or easier viewing, one of the nice text editors installed on the cluster is sublime.

subl  <filename> &

This will open up a nice GUI based text editors that has all the bells and whistles like find/replace, go to line, and such. The & sign means to gedit in the background so that you can still type and do things in the terminal window you launched gedit from.

3. On your Mac, you also have several options. The one I recommend is Text Wrangler, which is now called BBEdit. Make sure to install the command line editor. You can use this to open any text file. From the Finder, by right clicking, selecting ‘Open With’, and then BBEdit. The main reasons I recommend BBEdit are it has a powerful find/replace function and has a unix friendly newline character. In addition, it has a command line tool, so that when you are in a terminal, you can open things right there, just like sublime on the cluster, via:

edit  <filename>

It will also let you edit ‘protected’ files by prompting you for a username and password, where other programs like the default text editor will often just deny you permission.

How do I change or reset my password?

To reset or change your password, use the Research Computing website here.

What if I want to VPN to the NCF from a different computer than usual?

The openauth token code required for the two-factor authentication is specific to your username. Therefore, if you want to VPN from a different machine, you will have to set this up again. An alternative is to get the openauth app for your iphone, blackberry, or android. The instructions for doing so are here.

How do I check how much space I have left?

From ncfood or an SSH session, type:

df –h <directory_you_want_to_check>

How do I compress my dicoms to save space?

From ncfood or an SSH session, go to the directory that contains all of your dicoms. Type:

tar -czvf name.tar.gz what_you_want_to_tar

For instance: tar -czvf mydicoms.tar.gz subjid* or tar -czvf mydicoms.tar.gz *.dcm

To uncompress them:  tar -xzvf name.tar.gz

How do I use the internet during VPN or from ncfood?

NCF system users will have access the Internet while connected to the NCF VPN, with any compatible web browser that will get an automated proxy configuration. For most browsers you should not have to do anything. You should also have access to your email. If this is not true please contact rchelp [at] fas [dot] harvard [dot] edu. There maybe some issues with the VPN if you have to access other remote secure networks simultaneously. In that case, please contact rchelp [at] fas [dot] harvard [dot] edu. You should also be able to access the internet from the remote desktop interface. If you launch firefox and get the message it is already running, see here If you experience any trouble accessing the internet, please contact rchelp [at] fas [dot] harvard [dot] edu.

How do I set or change my SPM version?

You can change your SPM version similar to any other brain analysis software using the tools described above.  However, you also need to add the SPM version to your matlab path.  You can do this by using one of the variables set in the default unix environment (see here), $_HVD_SPM_DIR.  To check what that variable is set to, type:

echo $_HVD_SPM_DIR

Remember, if you want to use a different version of SPM on future logins and in different terminals, you must add it to your .bashrc file. Once you have the SPM you want you can add this variable to your ~/matlab/startup.m file (See here for editing files).


This will prepend SPM and its subdirectories to your matlab path, which means it will supersede any version you had previously set in your path.  You should be aware that if you make changes to your path in matlab and then save it, this version of spm will become part of your 'permanent' path, as it was added on the fly at startup, but then you just saved the whole current thing.  This can become a problem if you are swiches versions back and forth.  This is also true of Freesurfer, who likes to add things to your matlab path, so make sure to check this occasionally and make sure mutliple things aren't added (via file - set path in matlab).

How do I streamline my SPM analysis?

A collaboration with IQSS (Alex Storer), a previous graduate student, Caitlin Carey, and our local Tim O'Keefe have resulted in a set of python scripts to help you with your SPM analysis. They are designed to take a batch script you create for a single subject, and apply it to a bunch of subjects. They start by downloading your data from CBSCentral. So even if you don't want to use them for analysis, you might want to use them for grabbing your data and converting to SPM niftis. The instructions for using them are located on GitHub. The scripts do not have to be downloaded, but you do have to load the module for them. In your script, or in your terminal window, you will need to have the following commands before you can use or even see them.

source new-modules.sh
module load ncf
module load cbs_spm/master-ncf

The first two lines might become optional, but are needed at the moment.

The instructions for use are located here: https://github.com/harvardinformatics/CBS_SPM/blob/master/README.org

Essentially, they replace the path information in your batch script with that of the new subject. You can easily check the new batch created, if you want to do anything nonstandard. They have been tested with basic preprocessing (including SPM12 where you can include slice timing information for SMS/multiband scans), through your first level analysis.

Firefox won’t open because it thinks it is already running.

The reason this happens is because Firefox uses one profile by default, and this profile gets “locked” when in use. To resolve this issues, when logged into the ncf, open a terminal session and type in the command line:

firefox -profilemanager

A “Firefox – Choose your profile ” dialogue box will come up. Click on “Profile” -> “next” -> fill in a description, such as “second”, then click “finish” Then highlight the new profile, by clicking on it once with the mouse, and click on “Start firefox” Firefox should start up now.

Gedit is generally misbehaving.

Most issues, like random warnings, not opening, or not copy pasting correctly can be solved by deleting your local gedit preference file.

rm -R .gnome2/gedit/*

Once on the NCF, I can’t start applications such as Firefox or Matlab.

There are a few possibilities:

1) Please make sure that you are either typing the full path, or that the application is in your path. To check if an application is in your path, type:

which <program_or_script_name>

If that returns a path for the application, then you shouldn’t need the whole path, see other possibilities below.

2) Please verify that your home directory has not reached it’s max quota. Go here for instructions on checking your space.

3) If you are remotely logged in, the problem could involve X11 forwarding. On the Mac, make sure that you used the –X or –Y flag when sshing (example). On the PC if you are using Putty, there should be an option to check ‘Enable X11 Forwarding).

4) Make sure you are sourcing the default environment that includes most packages and sets your path.  Go here to see what it should look like. 

4) If you are still having issues, email rchelp [at] fas [dot] harvard [dot] edu.

I tried to ssh to a login node and it gave me a scary message about the token or IP address changing, what should I do?

RC actually has a pretty good FAQ for this,which you can check out for up to date instructions. The error message looks something like:

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @ WARNING: POSSIBLE DNS SPOOFING DETECTED! @ @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ The RSA host key for ncfws01.rc.fas.harvard.edu has changed, and the key for the corresponding IP address has a different value. This could either mean that DNS SPOOFING is happening or the IP address for the host and its host key have changed at the same time. Offending key for IP in /Users/stephanie/.ssh/known_hosts:8 @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @ @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY! Someone could be eavesdropping on you right now (man-in-the-middle attack)! It is also possible that the RSA host key has just been changed. The fingerprint for the RSA key sent by the remote host is ee:bf:41:7d:3f:00:29:1a:8f:05:99:b2:51:28:a0:93. Please contact your system administrator. Add correct host key in /Users/stephanie/.ssh/known_hosts to get rid of this message. Offending key in /Users/stephanie/.ssh/known_hosts:16 RSA host key for ncfws01.rc.fas.harvard.edu has changed and you have requested strict checking. Host key verification failed.

To fix it, you need to edit the file it tells you: /Users/username/.ssh/known_hosts.

For instance, if you got this message when trying to ssh to ncfws01.rs.fas.harvard.edu (which doesn't exist anymore!!), you would open up the requested file and delete the line containing information for that login node (highlighted in gray below).