Ssh fails for one of two users on the same server. Post: 303037390

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Top Forums Shell Programming and Scripting Ssh fails for one of two users on the same server. Post 303037390 by rbatte1 on Wednesday 31st of July 2019 06:48:04 AM

07-31-2019

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The client side needs to generate the key-pairs and the server side needs to have the public keys for each acceptable key-pair added to ~/.ssh/authorized_keys file for the user account on the server being connected to. Never copy the private key between users or servers (except for backups I suppose) because these are the critical identity proof for the client. If misused, you have little idea what has used them. If you feel that the integrity might have been compromised on a client, you can change the public key for just that client on the server rather than on all the clients, which is prone to error from clients being switched off or you not having the rights to sign on to the client to change the keys etc.

The server uses the keys for the requested user in ~/.ssh/authorized_keys in turn to encrypt a challenge to any connecting client. A client can prove it's identity by decrypting the challenge and responding, so keep the private key (used for decryption) separate for each user of each client and you will know what is permitted or not. The server can have multiple public keys authorised for any particular account by adding the multiple public keys on separate lines in ~/.ssh/authorized_keys for the target user(s) that the client is permitted to connect to.

You can go further and the client could generate multiple pairs of keys and save them to different pairs of files. The client can then be directed to use the appropriate private key for each user/server combination it wishes to connect to. Some may think this as overkill but it is an option should you deem it necessary and it is your choice. We use single client key-pairs for many things but specific user/server key-pairs for our most critical connections.

Remember that security is important and SSH (and related services) enforce this. Generally try to ensure that client's ~/.ssh directory and contents must not be readable by anyone else. Open permissions get rejected. Similar for the target account on the server. Openning permissions up to 'help' it will not work.

I hope that this helps,
Robin

rbatte1

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LEARN ABOUT FREEBSD

ssh-copy-id

SSH-COPY-ID(1)						    BSD General Commands Manual 					    SSH-COPY-ID(1)

NAME

     ssh-copy-id -- copy public keys to a remote host

SYNOPSIS

     ssh-copy-id [-lv] [-i keyfile] [-o option] [-p port] [user@]hostname

DESCRIPTION

     The ssh-copy-id utility copies public keys to a remote host's ~/.ssh/authorized_keys file (creating the file and directory, if required).

     The following options are available:

     -i file
	     Copy the public key contained in file.  This option can be specified multiple times and can be combined with the -l option.  If a
	     private key is specified and a public key is found then the public key will be used.

     -l      Copy the keys currently held by ssh-agent(1).  This is the default if the -i option was not specified.

     -o ssh-option
	     Pass this option directly to ssh(1).  This option can be specified multiple times.

     -p port
	     Connect to the specified port on the remote host instead of the default.

     -v      Pass -v to ssh(1).

     The remaining arguments are a list of remote hosts to connect to, each one optionally qualified by a user name.

EXIT STATUS

     The ssh-copy-id utility exits 0 on success, and >0 if an error occurs.

EXAMPLES

     To send a specific key to multiple hosts:
	   $ ssh-copy-id -i /path/to/keyfile.pub user@host1 user@host2 user@host3

HISTORY

     The ssh-copy-id utility was written by Eitan Adler <eadler@FreeBSD.org> as a drop-in replacement for an existing utility included with
     OpenSSH.

BSD
								 February 28, 2014							       BSD