SSH is short for Secure Shell. It allows you to execute commands on a remote computer and much more. It uses encryption for the data transfer.
- SSH is more secure than telnet thus it is recommended for use with Linux systems.
- In Red Hat & fedora these RPM packages must be installed: openssh-clients, openssh
Main article: Using ssh
# ssh firstname.lastname@example.org
In this case, 192.168.0.2 is your target's IP address, where you have a user youruser. You can also use a hostname, in our examples target instead of an IP address. 1st time you log in to a system a mesage will come up:
The authenticity of host 'xxxxx' can't be established. DSA key fingerprint is 94:68:3a:3a:bc:f3:9a:9b:01:5d:b3:07:38:e2:11:0c. Are you sure you want to continue connecting (yes/no)? <-- type in y for yes or n for no
If you type yes then:
Warning: Permanently added 'xxxxxxxx' (RSA) to the list of known hosts.
2. Now type in the password
3. If you don't want to log in but you want to execute a command, do this:
# ssh youruser@target date
You can even run GUI programs with this. For example, if you wanted to run a GUI text editor like kate or a web browser like firefox, try something like this:
ssh -X username@servername firefox
This will cause firefox to load on the remote machine, however the interface will be forwarded to your local machine giving you remote control over an encrypted ssh connection. Pretty cool, huh? ;-) If this doesn't work out-of-box then it probably means that it is turned off in the openssh server configuration.
If ssh does not work, you may have switched on the firewall. Make sure your target computer has port 22 open towards your computer:
telnet target 22 Trying 192.168.0.2... Connected to target. Escape character is '^]'. SSH-2.0-OpenSSH_4.6
SSH Client Software
Some implementations for other OS:
- SSHDOS - client for MS-DOS.
- PuTTY - client for console access and X-Windows forwarding on Windows.
- WinSCP  - open source SFTP and SCP client.
- The Cygwin UNIX environment for Windows includes OpenSSH's client and server.
Troubleshooting SSH Connections
Get debug information
SSH clients and servers can generate a lot of debug information.
On the server, kill sshd, and then start the server in debug mode.
$ killall sshd PID $ /usr/sbin/sshd -ddde
Leave the window open, so you can see the output it generates.
Then on the client, run:
$ ssh -vvv (target-host)
ssh -X does not work
If ssh -X works, but you still do not get the graphical display from your remote machine, check /etc/ssh/sshd_config. There must be a line