Tools

SSH Cheat Sheet — Keys, Connections, and Tunnels

SSH is how you reach remote machines securely. This reference covers connecting, key management, the config file that saves you typing, and tunnelling.

Put it into practice with the matching tool.

Calculate chmod permissions →

Connecting

ssh user@hostConnect to a host

ssh -p 2222 user@hostUse a non-default port

ssh -i ~/.ssh/key user@hostUse a specific private key

ssh user@host "ls -la"Run one command and exit

ssh -v user@hostVerbose — the first step when debugging

ssh -A user@hostForward your agent — use only on hosts you trust

ssh -J jump@bastion user@hostConnect through a jump host

~.Type this on a new line to kill a frozen session

Keys

ssh-keygen -t ed25519 -C "[email protected]"Generate a modern key pair

ssh-keygen -t rsa -b 4096RSA, for systems that do not support ed25519

ssh-copy-id user@hostInstall your public key on the server

ssh-keygen -p -f ~/.ssh/id_ed25519Change a key's passphrase

ssh-keygen -l -f key.pubShow a key's fingerprint

ssh-keygen -y -f key > key.pubRecover the public key from a private key

ssh-add ~/.ssh/id_ed25519Add a key to the running agent

ssh-add -lList keys the agent currently holds

~/.ssh/config

Host myserverA short alias — then just: ssh myserver

HostName 203.0.113.10The real address

User deployDefault username

Port 2222Default port

IdentityFile ~/.ssh/deploy_keyKey to use for this host

ProxyJump bastionAlways connect via a jump host

ServerAliveInterval 60Keep idle connections from dropping

Host *Settings applied to every host

Port forwarding

-L 8080:localhost:80Local — reach a remote service at localhost:8080

-L 5432:db.internal:5432Reach a database only the server can see

-R 9000:localhost:3000Remote — expose your local port on the server

-D 1080Dynamic — a SOCKS proxy through the server

-NNo remote command — tunnel only

-fDrop into the background once connected

Copying files

scp file user@host:/path/Copy a file to the server

scp user@host:/path/file .Copy a file from the server

scp -r dir user@host:/path/Copy a directory

rsync -avz dir/ user@host:/path/Sync — faster and resumable

rsync -avz --delete src/ host:/dst/Mirror, removing files deleted locally

sftp user@hostInteractive file transfer session

Permissions & troubleshooting

chmod 700 ~/.sshSSH refuses to work if this is too open

chmod 600 ~/.ssh/id_ed25519Private keys must not be group/world readable

chmod 644 ~/.ssh/authorized_keysPublic key list on the server

ssh-keygen -R hostRemove a stale host key after a rebuild

Permission denied (publickey)Key not installed, wrong key, or bad permissions

More cheat sheets

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