SSH

ssh, the secure shell

Reviewed by Bil Hays 6.29.2017

The ssh client program is a secure shell replacement for the telnet and rlogin and rsh programs.  You should never use telnet or rlogin to login to UNIX machines, because these programs are insecure.  Both telnet and rlogin send your user name and password in the clear text over the network, and this information can be “sniffed” by someone.  Below is information about ssh on UNIX, Windows, and Macs.

ssh on Linux

The ssh program we use is the Open SSH software:

http://openssh.com

To use ssh on a UNIX system, type “ssh hostname”.  You will be prompted for your password, which ssh encrypts before sending it over the network.  The first time you login to a UNIX system, you will also be prompted to “register” the remote machine’s “public key”; which in UNIX is stored in your home directory in the $HOME/.ssh/known_hosts.  Answer “Yes” so you will not be prompted to register on subsequent logins.

The ssh program is available on all department UNIX machines under /usr/local/bin/ssh.  There are many features and utility programs that are in the ssh suite.  For further information, see the online manual at the Open SSH web site.

There is a secure replacement for the UNIX ftp client called “sftp”.  You can use this to connect to Computer Science UNIX systems.  Like telnet, the standard ftp clients send your password over the internet in clear text.  Both ftp and sftp have a command line interface once you connect.  The sftp commands are a bit different from the standard ftp commands; enter “?” when using the sftp client for help on the commands.  See our article on SFTP for more information.

ssh on Windows

***We used to recommend SSH SecureShell, that software is no longer supported and will not connect to many of our servers.

Our current recommends ssh client for windows is Putty, and we are transitioning to installing it on all windows computers. It works very much the same as SecureCRT described below.

If you are logging into a UNIX machine from a Windows platform, you should use the SecureCRT terminal program to start up an ssh window.  (While SecureCRT also supports telnet, you should only use ssh; otherwise you may be giving a hacker your password.)  SecureCRT is installed by default on all department Windows systems.

To connect to a UNIX machine, start up SecureCRT, click the “File” menu, and select “Quick Connect”.  You will be presented with the following (under version 6.5):

copy_of_SecureCRT

Enter the hostname of the system you want to log into, e.g., login.cs.unc.edu; enter your UNIX login name, and click “Connect”.

The campus has a site license for SecureCRT that allows UNC employees and students to run SecureCRT on their personal systems.  See the campus shareware web page for more info on SecureCRT:

https://shareware.unc.edu/software.html#s

Questions

Please send email to help@cs.unc.edu if you have any questions on how to use these programs.