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Tips for Remote Sessions

SSH from outside Oxford

The Oxford supercomputers and office machines cannot be directly accessed from outside the Oxford network, and wrangling with VPNs is often nightmarish. Thankfully, you can register for the "Linux service" and from outside the Oxford network, ssh directly to

ssh [USER]@linux.ox.ac.uk

where [USER] is your SSO account name. Once connected, your session will be inside the Oxford firewall, and you can subsequently SSH again into the office machines or the ARC supercomputers.

SSH to a specific directory

Linux and MacOS

To SSH directly into a target remote directory [DIR], run:

ssh [USER]@[ADDRESS] "cd [DIR]; bash"

It is convenient to save this as a bash script to run each time when connecting. For example, I access ARCUS-B via a script ~/arcusb_connect.sh with contents:

ssh [email protected] "cd /data/oums-quantopo/corp2627 ; bash"

which is previously given permission to run via chmod +x arcusb_connect.sh

SSH without passphrase

Linux and MacOS

Do not use passphraseless SSH on the ARC facilities, to avoid fiascos like this. Please only use the below guide for access to the office workstations, as required for remote Mathematica kernels.

These instructions currently do NOT apply to Igor.

Punching in your password every time you SSH to the same machine can be a chore. We have RSA keys, let's use them! Here we'll setup passphrase-free SSH. This is sometimes necessary for running Mathematica kernels on remote machines, like Victor and Fritz.

All the below commands are to be entered in your local machine's terminal, unless specified otherwise.

  1. Ensure you have an RSA key:

    ssh-keygen -t rsa

    Do not overwrite your existing key if prompted (hit n).

  2. Add your key to the remote machine (USER@ADDRESS):

    cat ~/.ssh/id_rsa.pub | ssh USER@ADDRESS 'cat >> ~/.ssh/authorized_keys'

    If this fails, reporting "directory nonexistent", then first SSH into the remote machine:

    ssh USER@ADDRESS

    then on the remote machine, run:

    mkdir ~/.ssh; chmod 700 ~/.ssh; touch ~/.ssh/authorized_keys; chmod 600 ~/.ssh/authorized_keys

  3. Add the key to the SSH agent:

    ssh-add -K ~/.ssh/id_rsa

  4. If you're on MacOS, you may additionally need to permit the SSH agent to use the key chain. Do this by editing ~/.ssh/config to feature:

    Host *
    UseKeychain yes

  5. You should now be able to SSH straight into the remote machine without a password prompt!

    ssh USER@ADDRESS

Mount remote drive

MacOS

Copying files back and forth with a remote machine can be a pain. Mounting the remote drive will make it appear as a regular directory on your client machine, so you can edit remote files in software as if they were local.

All the below commands are to be entered in your local machine's terminal.

  1. Ensure you have Homebrew installed:

    ruby -e "$(curl -fsSL https://raw.github.com/mxcl/homebrew/go)"

  2. Install osxfuse from Homebrew:

    brew cask install osxfuse
    1. Restart your computer

    I know I know, grr.

  3. Install sshfs from Homebrew:

    brew install sshfs

At this point, you can now use sshfs to create remote mounts. However, it's best to create a script to activate the mount, which will be deactivated each time you lose internet or shutdown your machine. Here's how:

  1. Create a new MountDir directory on the desktop (or elsewhere) which will become the remote filesystem:

    mkdir ~/Desktop/MountDir

    This folder must exist when you attempt to activate the remote mount, so don't delete it!

  2. Create a mounter.sh script (via sudo nano ~/mounter.sh) with contents:

    sudo sshfs -o allow_other,defer_permissions USER@ADDRESS:REMOTEDIR ~/Desktop/MountDir

    where USER@ADDRESS is your usual SSH target info, and REMOTEDIR is the directory on the remote machine to be mounted locally; this should be the root of your personal directory on the remote machine. You will only be able to access files/folders within this directory through the remote mount.

    For example, my command to mount my drive on Victor is

    sudo sshfs -o allow_other,defer_permissions [email protected]:/home/tyson ~/Desktop/MountDir

    To exit nano, hit keys control x then y then Enter.

  3. Give the mounter.sh script permissions to run:

    chmod +x ~/mounter.sh

The setup is complete. To activate the mount, run:

~/mounter.sh

This will require you enter both your MacOS root password, and your password for the remote machine. Afterward MountDir on your Desktop will have changed to OXFUSE and contain your remote directory.

To unmount (not often necessary), run:

sudo umount ~/Desktop/MountDir

Spontaneous disconnection will sometimes require you to restart your machine in order to run ~/mounter.sh again.