Difference between revisions of "SSH"

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From the local machine to a remote machine:
 
From the local machine to a remote machine:
  
*<code>scp '''FileName'<nowiki/>'''''user@MACHINENAME:Destination'<nowiki/>''</code>
+
*<code>scp '''FileName''' '''<nowiki>user@MACHINENAME:Destination</nowiki>'''</code>
  
 
From a remote machine to the local machine:
 
From a remote machine to the local machine:
  
*<code>scp '''user@MACHINENAME:FileNameDestination'''</code>
+
*<code>scp '''user@MACHINENAME:FileName Destination'''</code>
  
 
From a remote machine to another remote machine:
 
From a remote machine to another remote machine:

Revision as of 19:38, 21 September 2021

How To Enable SSH in Linux Mint

Passwordless SSH

Using SSH to get stuff done

Make it easier to connect

Don't use password authentication. Use Public Key Authentication.

  • ssh-keygen
    • (Note: You only have to do this step once on any particular machine.)
    • The passphrase is optional.
  • ssh-copy-id user@MACHINENAME
    • This can be done for as many remote machines as you like.

This will simplify your life. From this point on, any time you SSH into (or SCP to/from etc...) the machine known as MACHINENAME while working at the machine you've done this on, you'll be automagically authenticated.

Signing in to a machine

Pretty straightforward:

  • ssh user@MACHINENAME

This will securely give you a terminal session of the remote machine. (Much like good old telnet... But not quite so sketchily insecure.)

Executing commands remotely

Also, pretty straightforward...

  • ssh user@MACHINENAME "Command to be executed"

One thing to note...

If you want to execute a command remotely that requires sudo, you'll have to add a -t to the command line or else sudo with tell you where to go.

  • ssh -t user@MACHINENAME "Command to be executed"

This is because sudo intentionally will NOT run without a local terminal session.

Transferring files

There are at least 3 ways you can securely transfer files using SSH (via the SCP command)

From the local machine to a remote machine:

  • scp FileName user@MACHINENAME:Destination

From a remote machine to the local machine:

  • scp user@MACHINENAME:FileName Destination

From a remote machine to another remote machine:

  • scp user@MACHINENAME:FileName user@OTHERMACHINENAME:Destination

Starting to see a pattern?

As a bonus, RSYNC will use SSH as a transport layer.

Port forwarding (AKA Tunnelling)

Working on this part...

One description

An example

Troubleshooting

(somebody remind me to clean this crap up & make it easier to follow...)

If you get crap like:

Warning: the ECDSA host key for '<snip>' differs from the key for the IP address '<snip>'
Offending key for IP in /home/<snip>/.ssh/known_hosts:14
Matching host key in /home/<snip>/.ssh/known_hosts:12
Are you sure you want to continue connecting (yes/no)?

or maybe:

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that a host key has just been changed.
The fingerprint for the RSA key sent by the remote host is
SHA256:'<snip>'
Please contact your system administrator.
Add correct host key in /home/user/.ssh/known_hosts to get rid of this message.
Offending RSA key in /home/user/.ssh/known_hosts:102
  remove with:
  ssh-keygen -f "/home/user/.ssh/known_hosts" -R '<snip>'
RSA host key for '<snip>' has changed and you have requested strict checking.
Host key verification failed.

when you try to ssh to a machine...

  • sudo ssh-keygen -f ~/.ssh/known_hosts -R HOSTIP

Messages like:

Warning: the RSA host key for '<snip>' differs from the key for the IP address '<snip>'
Offending key for IP in /home/user/.ssh/known_hosts:102
Matching host key in /home/user/.ssh/known_hosts:103
Are you sure you want to continue connecting (yes/no)? 

mean that you have an extra entry in your known_hosts file & indicates the line you want to delete...

If you see:

  • Failed to add the host to the list of known hosts (/Users/USER/.ssh/known_hosts).

Check permissions & ownership on that file...

Some SSH reference Links