Accessing Remote Shell

So far, we have been accessing the Unix computing environment locally, on your laptop or desktop computer.

Using the shell, however, opens up a whole new world -- you can now access a remote computer over the Internet using the same interface.

Let's try this out, using one of the two remote servers:

sunfire

A Unix computing server called sunfire, hosted by the School of Computing. To access this, you need to have a SoC Unix Account. If you do not have one yet, you can create a new account here: https://mysoc.nus.edu.sg/~newacct

After that, activate "General Unix Servers" and "The SoC Compute Cluster" in MySoC here: https://mysoc.nus.edu.sg/~myacct/services.cgi

sunfire is a shared machine running Solaris.

To log into sunfire, type:

$ ssh sunfire.comp.nus.edu.sg
or 
$ ssh <username>@sunfire.comp.nus.edu.sg

The first option above assumes your SoC Unix account name is the same as your username on your local machine (Remember we advised you to choose the same username when you installed WSL? This is why!). In the second option, we have to explicitly provide our user name. For instance, 

$ ssh ooiwt@sunfire.comp.nus.edu.sg

These commands are too long to type so you could add an alias for this command into your ~/.bashrc.

sdf.org

For those students who do not have a NUSNET or SoC account, as a backup, you can apply for an account at public access Unix system provided by the Super Dimension Fortress at http://www.sdf.org.

Once you receive your account, you can ssh into sdf.org by

$ ssh sdf.org

Secure Shell

ssh stands for secure shell. It is called secure as it encrypts all communications between you and the remote server. It is an efficient way to access a remote computer since only texts are transmitted, not graphics.

The first time you access a remote computer using ssh, it will ask you a question, which looks sometimes like this: 

The authenticity of host 'sunfire (137.132.80.55)' can't be established.
RSA key fingerprint is SHA256:UUyiI25neTV5AT/q3CJi0BAA4ztfo+7doi77bkzpLJ4.
Are you sure you want to continue connecting (yes/no/[fingerprint])?

Type yes then hit Enter. You won't be asked the same question again.

Once you log in, you will be presented the same interface as you are used to -- a command prompt. You can do everything that you have learned at this command prompt, with the only difference being you are doing it on a remote computer (aka remote host or remote server).

Transferring Files Back and Forth

Secure copy, or scp, is one way to transfer files between the remote host and your local computer for archiving or storage. Let's say you want to transfer jfk.txt from the current working directory to your remote directory, then, on your local computer, run:

$ scp jfk.txt sunfire.comp.nus.edu.sg:~/

scp behaves just like cp, except that we add sunfire.comp.nus.edu.sg: in front of a path (add <username>@ as necessary) to indicate the name of the remote host to copy the files to. The path ~/ now refers to the home directory on the remote host.

If you have files with the same name in the remote directory, the files will be overwritten without warning. I have lost my code a few times due to scp.

scp supports -r (recursive copy) as well.