Secure Shell (ssh)
Secure Shell is a cryptographic network protocol for operating network services securely over an unsecured network.
Table of Contents
SSH provides a secure connection between the host machine and a remote server.
ssh -i <path-to-private-key> <host> where <path-to-private-key> can be ~/.ssh/id_rsa for instance.
Authentication key pairs
Algorithms and key size
Currently, the relevant algorithms are rsa and ed25519.
The algorithm is selected using the -t flag and key size using the -b option:
ssh-keygen -t rsa -b 4096ssh-keygen -t ed25519size is fixed for this algorithm, no need to specify it.
Copy pubkey to server
To use public key authentication, the public key must be copied to a server and installed in an authorizedkeys file.
This can be conveniently done using the ssh-copy-id tool.
ssh-copy-id -i ~/.ssh/id_rsa user@host
File tranfer
Copy a file from/to the remote host and vice-versa.
- Local to host:
scp file host:path - Host to local:
scp host:path file
Configuration file
When connecting to multiple remote systems over SSH, it can be difficult to remember all of the remote IP addresses, different usernames and ports.
To better manage those connections, we can create a config file at /.ssh/config to shorten the connection command.
Example:
Host targaryen
HostName 192.168.1.10
User daenerys
Port 7654
IdentityFile ~/.ssh/targaryen.key
Host tyrell
HostName 192.168.10.20
Host martell
HostName 192.168.10.50
Host *ell
user oberyn
Host * !martell
LogLevel INFO
Host *
User root
Compression yes
Then we can simply do ssh targaryen to remotely connect to the 192.168.1.10 host.