What is the SSH command line tool? (OpenSsh)

Host Key Not Cached Putty


The ssh cli is the ssh client of openssh



See OpenSSH installation


  • user's private key location: ~/.ssh/id_rsa


ssh-agent is a background process where you can store keys (encrypted by a passphrase or not).


You can check which configuration files is loaded by initiating a SSH connection with the verbose flag. Example

ssh -v badDestination # badDestination is a unknown hostname and will force ssh to stop early
OpenSSH_8.4p1 Debian-5+deb11u3, OpenSSL 1.1.1n  15 Mar 2022
debug1: Reading configuration data /Users/YOU/.ssh/config
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: include /etc/ssh/ssh_config.d/*.conf matched no files
debug1: /etc/ssh/ssh_config line 21: Applying options for *

As you can see with the above output, there are 2 standard loaded configurations

  • a User scoped at ~/.ssh/config
touch ~/.ssh/config
chmod 600 ~/.ssh/config
vim ~/.ssh/config
  • a System wide at /etc/ssh/ssh_config
# This is the ssh client system-wide configuration file.  See
# ssh_config(5) for more information.  This file provides defaults for
# users, and the values can be changed in per-user configuration files
# or on the command line.

# Configuration data is parsed as follows:
#  1. command line options
#  2. user-specific file
#  3. system-wide file
# Any configuration value is only changed the first time it is set.
# Thus, host-specific definitions should be at the beginning of the
# configuration file, and defaults at the end.

# Site-wide defaults for some commonly used options.  For a comprehensive
# list of available options, their meanings and defaults, please see the
# ssh_config(5) man page.

Host *
#   ForwardAgent no
#   ForwardX11 no
#   ForwardX11Trusted yes
#   RhostsRSAAuthentication no
#   RSAAuthentication yes
#   PasswordAuthentication yes
#   HostbasedAuthentication no
#   GSSAPIAuthentication no
#   GSSAPIDelegateCredentials no
#   GSSAPIKeyExchange no
#   GSSAPITrustDNS no
#   BatchMode no
#   CheckHostIP yes
#   AddressFamily any
#   ConnectTimeout 0
#   StrictHostKeyChecking ask
#   IdentityFile ~/.ssh/identity
#   IdentityFile ~/.ssh/id_rsa
#   IdentityFile ~/.ssh/id_dsa
#   IdentityFile ~/.ssh/id_ecdsa
#   IdentityFile ~/.ssh/id_ed25519
#   Port 22
#   Protocol 2
#   Cipher 3des
#   Ciphers aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc
#   MACs hmac-md5,hmac-sha1,[email protected],hmac-ripemd160
#   EscapeChar ~
#   Tunnel no
#   TunnelDevice any:any
#   PermitLocalCommand no
#   VisualHostKey no
#   ProxyCommand ssh -q -W %h:%p gateway.example.com
#   RekeyLimit 1G 1h
    SendEnv LANG LC_*
    HashKnownHosts yes
    GSSAPIAuthentication yes
    GSSAPIDelegateCredentials no

Connect / Login

ssh domain\username@servername  -p 3022

Logging with a private key

  • Posix Shell
ssh -i ~/.ssh/private_key.pem user@hostname
  • Powsershell
ssh -i $env:USERPROFILE\.ssh\private_key user@hostname


Executing a remote command

ssh user@host "command -arg1 'arg1value' -arg2 'arg2 value'"

Don't forget the quote to bypass the expansion mechanism


ssh -vvv hostname

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