SSH and Remote Access

SSH is the normal way into Linux hosts. You should be comfortable connecting, copying files, and checking client-side config quickly.

Core commands

ssh user@host
ssh -i ~/.ssh/key user@host    # connect with a specific private key
scp file.txt user@host:/tmp/   # copy a local file to the remote host
scp user@host:/var/log/app.log .  # copy a remote file back locally
rsync -av ./dir/ user@host:/srv/dir/  # sync a local directory to the remote host
ssh-copy-id user@host          # install your public key on the remote host
ssh -v user@host               # connect with verbose debug output

A simple SSH config

Host web-01
  HostName 10.0.0.25
  User deploy
  IdentityFile ~/.ssh/id_ed25519
  Port 2222

Jump hosts

ssh -J bastion-user@bastion target-user@target

ProxyJump bastion-user@bastion

High-value checks

See the effective SSH client config for a host:

ssh -G <host>   # print the effective SSH client config for that host

Test with verbose output:

ssh -v user@host

Clear a stale known_hosts entry after a host key change:

ssh-keygen -R <host>

What matters

• SSH keys are preferred over passwords.
• ~/.ssh/config saves time if you use jump hosts, custom ports, or named identities.
• rsync is usually the better default for repeated remote copies or directory syncs.
• ssh -v is often enough to tell whether the failure is DNS, TCP reachability, auth, or host key mismatch.
• A “host key changed” error usually means the remote host was rebuilt, reprovisioned, or you hit the wrong host for that name or IP.

Common mistake

Do not debug SSH only from the server side. Client-side config, wrong key selection, or a stale known host entry are common causes.