SecureShell – SSH

Description

• TCP/IP port 22
• sshd ‑ ssh server
  • package openssh-server
  • default sshd server config /etc/ssh/sshd_config
• ssh ‑ ssh client
  • package openssh-client
  • default ssh client config /etc/ssh/ssh_config or ~/.ssh/config

Usage

# -v = verbose mode for debugging
# -4 = forces IPv4
# -6 = forces IPv6
# -i = specify the identity private key
# -p = port
ssh user@HOST
ssh -i private_key_file user@HOST
ssh HOST                  # if the ssh keys are already copied in the server

• Generating the SSH keys ‑ ssh-keygen

# -t = type of key, dsa, ecdsa, ecdsa-sk, ed25519, ed25519-sk, rsa, rsa-sha2-512(DEFAULT)
# -b = Key length
# -f = Specify file to write to
# -C = comment
ssh-keygen -t rsa -b 4096
ssh-keygen -t ed25519

• Securely copying public SSH keys ‑ ssh-copy-id

# -i = Specify the ssh key file
# -p = Port to login
ssh-copy-id -i ~/.ssh/id_rsa.pub user@HOST

• scp & sftp
• SSH Tunneling

# Any traffic send in the local machine 3306 is forwarded to 5432 port in the remote machine
ssh -L [local_port]:[destination_server_ip]:[remote_port] [username]@[hostname_or_IP]
ssh -L 3306:10.10.10.10:5432 user@hostname

# Remote port forward (any request direct in the remote machine port 3306 is forwarded to local machine 5432)
ssh -R [remote_port]:localhost:[local_port ssh_server_hostname]
ssh –R 3306:10.10.10.10:5432 user@hostname

Options

Options	Description
-i	specify private key, when doing key-based auth
-p	SSH port (default 22)
-v	enable verbose logging
-C	enable compression
-p	SSH port (default 22)

Installation

Distro/OS/Package Manager	Install Instruction
Centos/fedora(dnf, microdnf, rpm, yum)	yum install openssh openssh-server
Debian/ubuntu	apt install openssh-server openssh-client
Arch (pacman)	pacman -Sy openssh
Alpine (apk-docker)	apk add openssh

References

• Redhat Docs
• Ubuntu Docs