Remote Access to the CS Linux Machines

This page describes how to access the CS department's Linux machines remotely, i.e., how to use them if you are not sitting in front of them. For more about various options, or if anything described here doesn't work, see the section Questions below.

Contents

• What machines are available
• Logging in
  • From another UNIX/Linux system
  • From Windows
  • From Mac OS X
  
  
• Transferring files
  • From another UNIX/Linux system (command line)
  • From Windows (command line)
  • From Mac OS X (command line)
  • With a GUI program
  
  
• Remote access from off-campus
• Questions

What machines are available

The department maintains a number of computers that are accessible to anyone with an account on our system(s). Such machines include:

• The machines in the teaching labs (CSI 257, CSI 388, and CSI 488) and the other labs (CSI 270A, CSI 270L, and CSI 354). Almost all of these machines are dual-boot (Windows and Linux), so their availability for Linux remote access depends on which operating system is currently running. (You can check availability with the command ruptime; machines that show as “up” are available. Note however that output of this command includes both generally-available machines and some special-purpose machines such as faculty desktops and research machines to which you may not have access.)
• Several Linux-only machines housed by ITS. Ask your instructor or research supervisor for information about names and usage.

Logging in

From another UNIX/Linux system

To connect:

• From one department machine to another (say remoteMachine):

  ssh remoteMachine

• From another UNIX/Linux system:

  ssh username@remoteMachine.cs.trinity.edu

  where username is your username on the department machines.

The man page for ssh has complete information. Normally ssh will prompt you for a password; you can find instructions for setting up access using keys instead in my notes on passwordless login.

Once you've logged in, you can execute any text-based program (ls, vi, etc.). Depending on how your local machine is set up, you may also be able to run programs that need a graphical environment (firefox, gvim, etc.). If you have trouble, first try re-executing the ssh command with the -Y option and then ask for help if it doesn't work. Also note that running graphical-environment programs over a network is apt to be slow.

From Windows

What you need is a “terminal emulator” that can connect via SSH to a remote machine. You have some options:

• A simple option is KiTTY (a fork of PuTTY). Functionality is similar to what you get with the UNIX ssh command (i.e., a terminal window).

  It should be installed on all ITS-managed Windows machines on campus, including the department's Windows machines. (The icon is labeled PuTTY and shows a picture of two computers with something connecting them.)

  If you want to install it on your own computer, it's free and available at http://www.9bis.net/kitty.

  To use this program, start it up, make sure the SSH radio button is selected (probably on by default), type the name of the machine you want to access into the “Host name or IP address” box, and click “Open”. You should then get a terminal window prompting you for your (Linux) username and password. You may get an alarming message about possible security problems the first time you to try to access a remote machine and asking if you want to continue. You do.

  By default, what you get is a text-only window. If you want to run programs that require a graphical environment, you need to do two things:

  • Start an “X server”.¹ On ITS-managed machines, you do this by clicking the icon for VcXsrv. (You could probably install this on your own machine as well.)
  • Tell PuTTY/KiTTY before connecting that you want to use X11 forwarding: Navigate the menus on the left side to Connection->SSH->X11. Click the plus sign in front of SSH to view submenus. Then in the X11 forwarding configuration, check “Enable X11 forwarding”.
  Note, however, that running graphical-environment programs over a network is apt to be slow.

• A more complete solution is Cygwin (https://www.cygwin.com), which provides a UNIX-like environment under Windows. After it's installed, clicking on its icon should bring up something analogous to a terminal window under Linux, and most Linux commands should work, including the one for logging in described in section (Logging in) From another UNIX/Linux system.

  Supposedly if you install enough of Cygwin you will be able to log in with support for a graphical environment. (I have not tested this!)

• The bash shell that's part of the fairly recent Windows Subsystem for Linux (WSL). More about this option soon.

From Mac OS X

For Mac OS X, starting the Terminal application gives you something very like a Linux terminal window, from which you can connect using the command in section (Logging in) From another UNIX/Linux system. Running programs that need a graphical environment may or may not work; you may need to install additional packages.

Transferring files

From another UNIX/Linux system (command line)

Options here include:

• Command scp, which can transfer a single file or a set of files using a wildcard. It works much like cp, except that the source and destination can start with remoteMachine: or username@remoteMachine: For example, the command

  scp remoteMachine:/fullpath/*.txt .

  transfers a group of files matching the wildcard from remoteMachine to the current directory. The man page has more details and options.

• Command sftp, which opens an SFTP connection to another machine and allows you to move around in the local and remote filesystems and transfer multiple files, from local to remote and vice versa. Start it thus:

  sftp username@remoteMachine

  Once the connection is open, you can move around in the local or remote directories and transfer one or more files. Use command exit or control-D to end the connection. Command help lists available commands; some that are useful:
  • get and put transfer one or more files, from remote to local for get and from local to remote for put. Wildcards can be used, and newer versions of sftp support using the tab key for filename completion. Note that if a target file exists, it will be overwritten. Be careful!
  • ls works like the regular ls command to show information about the remote system; lls does the same for the local system.
  • cd works like the regular cd command to change directories on the remote system; lcd does the same for the local system.
  The man page for sftp has details of these and other commands.

From Windows (command line)

Tools that allow you to log in remotely typically come packaged with something for file transfer:

• If you're using PuTTY/KiTTY, it comes packaged with (Windows) command-line programs pscp and psftp. They can be found in the same directory as the main executable, and they work like the scp and sftp programs described in section (Transferring files) From another UNIX/Linux system (command line). (For ITS-managed machines, you should be able to find this directory by examining the properties of the shortcut on the desktop.)

• If you're using Cygwin, it should include implementations of the commands described in section (Transferring files) From another UNIX/Linux system (command line).

From Mac OS X (command line)

The commands in section (Transferring files) From another UNIX/Linux system (command line). should work in a Terminal window.

With a GUI program

If you want a program with a GUI, there are many options; the term to search for is probably “SFTP client”. We plan to install FileZilla on the department computers for fall 2019; we chose it because versions are available for Windows, Linux, and Mac OS X.

Remote access from off-campus

All of the above assumes that you are trying to log in from a computer inside the Trinity domain. For security reasons, ITS disallows direct access to most machines from outside this domain. There are two mechanisms for getting access from off-campus:

• The currently-recommended option for students is to use ITS's Virtual Desktop Infrastructure (VDI); it gives you a virtual Windows desktop, logically inside the Trinity domain, with a PuTTY/KiTTY icon you can use as described in in section (in) .

  To use it, point a Web browser at https://vdi.trinity.edu and follow the prompts.

  You should at some point be given a choice between “installing a client” and using an HTML interface. The HTML interface should work in any supported browser and is fine for occasional use. If you do this often, however, consider installing a client: Clients are available for several operating systems; they offer additional features (such as USB connections) and are apt to be faster.

  For more information, go to ITS's Service Catalog: There's a short text explanation and a link to a video with screenshots, plus information about connecting from different kinds of devices and about installing clients. (For Windows, note that you should not select the Windows 10 UWP version.)

• If this option is too cumbersome, talk to your instructor or research supervisor about other options.

Questions

For more information about anything described in this document, or if something doesn't work, you should probably start by talking to your instructor or research supervisor; if he or she can't help, communicate with the department's ITS liaison and occasional Linux admin Dr. Massingill (bmassing@trinity.edu).

Footnotes

... .¹

In UNIX-speak, an X server is a program that runs on a local machine and services graphical programs (the X clients) -- somewhat unusual use of “server” but reasonable in context?)