If you want to Administer Your Ubuntu Server Remotely in secure manner for your daily tasks or some maintenance for this you need to install SSH server.SSH provides you with the ability to remotely log in to your server and run commandsall over an encrypted channel. Plus, SSH offers a number of advanced functions that can make remote administration simpler.
Install SSH server in Ubuntu
sudo apt-get install openssh-server
This will complete the installation.the package will take care of creating the initial RSA and DSA keys you need, as well as providing you with a default SSH config.
Connecting to the server
Now you can connect to the server from other machines using the following command
ssh serveripaddress
Example
ssh 195.14.2.1
Configure SSH
The main configuration file located at /etc/ssh/sshd_config and the default configuration will enables remote root logins and X11 forwarding which is not good for your server security.So now we will disable these two options.
Disable remorte root logins
For this you need to search for the following line in /etc/ssh/sshd_config file
PermitRootLogin yes
and chnage this to the following one
PermitRootLogin no
Disable X11 forwarding
For this you need to search for the following line in /etc/ssh/sshd_config file
X11Forwarding yes
and chnage this to the following one
X11Forwarding no
After finishing your configuration you need to restart SSH server using the following command
sudo /etc/init.d/ssh restart
X11 Forwarding
If you want to use X11 Forwarding option so that you can connect your remote machine desktop using Xterm if you want to connect the X11 session you need to use the following command
ssh -X serveripaddress
Copy Files Securely using SCP
Another common need is to be able to copy files between servers you are administering. While you could set up FTP on all of the servers, this is a less-than-ideal and potentially insecure solution. SSH includes within it the capability to copy files using the scp command. This has the added benefit of copying the files over a secure channel along with taking advantage of any key-based authentication you might have already set up.
To copy a file to a remote machine use the following command
scp /path/to/file user@remotehost:/path/to/destination
If you need to copy from the remote host to the local host, reverse the above command
scp user@remotehost:/path/to/file /path/to/destination
if you need to copy an entire directory full of files to a remote location, use the -r argument
scp -r /path/to/directory/ user@remotehost:/path/to/destination/
If you are transferring logfiles or other highly compressible files, you might benefit from the -C argument. This turns on compression, which, while it will increase the CPU usage during the copy, should also increase the speed in which the file transfers.
Use the -l argument to limit how much bandwidth is used. Follow -l with the bandwidth you want to use in kilobits per second. So, to transfer a file and limit it to 256 Kbps use the following command
scp -l 256 /path/to/file user@remotehost:/path/to/destination