Linux commands

SSH toolbox#

Connecting#

Command	Does	Where
`ssh homeserver`	Log in through your home shortcut	Mac / PC
`ssh homeserver-remote`	Log in through Tailscale	Mac / PC
`ssh alex@192.168.1.50`	Log in without a shortcut	Mac / PC
`exit`	Log out (back to your own computer)	server
`ssh homeserver 'df -h /'`	Run one command and come back	Mac / PC
`ssh -v homeserver`	Connect and show every step (for fixing problems)	Mac / PC

Keys#

Command	Does	Where
`ssh-keygen -t ed25519 -f ~/.ssh/id_ed25519_homeserver -C "mac-homeserver"`	Make a new key pair	Mac / PC
`cat ~/.ssh/id_ed25519_homeserver.pub`	Show the public key (safe to share)	Mac / PC
`ssh-copy-id -i ~/.ssh/id_ed25519_homeserver.pub alex@homeserver.local`	Put the public key on the server (Mac/Linux)	Mac
`ssh-keygen -lf ~/.ssh/id_ed25519_homeserver.pub`	Fingerprint of a key	Mac / PC / server
`ssh-keygen -lf ~/.ssh/authorized_keys`	Fingerprints of every key allowed in	server
`ssh-keygen -p -f ~/.ssh/id_ed25519_homeserver`	Change a key's passphrase	Mac / PC
`ssh-add -l`	Keys loaded in the agent (no passphrase needed)	Mac / PC
`ssh-add --apple-use-keychain ~/.ssh/id_ed25519_homeserver`	Remember the passphrase in Keychain	Mac
`ssh-add -D`	Remove all keys from the agent	Mac / PC

The file ~/.ssh/authorized_keys on the server = one line per allowed device. Delete a line to lock that device out.

Shortcuts file#

~/.ssh/config on your Mac (C:\Users\alex\.ssh\config on Windows):

Host homeserver
    HostName homeserver.local
    User alex
    IdentityFile ~/.ssh/id_ed25519_homeserver
    IdentitiesOnly yes

ssh -G homeserver shows the final settings SSH will use, handy to check which key and address a shortcut picks.

Copying files#

Command	Does
`scp photo.jpg homeserver:~/`	Mac/PC → server home folder
`scp homeserver:~/report.txt .`	Server → the folder your terminal is in
`scp -r FOLDER homeserver:~/`	A whole folder
`rsync -avh --progress FOLDER/ homeserver:~/FOLDER/`	Copy only what changed; can resume (needs `rsync` on both sides)

Tunnels#

ssh -N -L 18095:127.0.0.1:8095 homeserver

-L  18095 : 127.0.0.1 : 8095
    │        │           └── port on the server
    │        └────────────── address as seen from the server (itself)
    └─────────────────────── port on YOUR computer: open http://127.0.0.1:18095
-N  just hold the tunnel open, no shell

Tunnel	Command	Then open
AI chat	`ssh -N -L 18095:127.0.0.1:8095 homeserver`	`http://127.0.0.1:18095`
Agent dashboard	`ssh -N -L 18765:127.0.0.1:8097 homeserver`	`http://127.0.0.1:18765`
Cockpit	`ssh -N -L 19090:127.0.0.1:9090 homeserver`	`http://127.0.0.1:19090`

Add -o ExitOnForwardFailure=yes to make it stop with an error instead of silently not working.

Server side#

Command	Does
`sudo sshd -t`	Check the SSH settings for mistakes (no output = OK)
`sudo sshd -T \| grep -i password`	What SSH really uses for a setting
`sudo systemctl reload ssh`	Apply new settings without dropping current logins
`sudo journalctl -u ssh -n 50`	Recent logins and failures
`who`	Who is logged in now
`last -n 20`	The last 20 logins

Common errors#

Message	Fix
`Permission denied (publickey)`	Wrong key or no key on the server. Check `ssh -G homeserver`, and `authorized_keys` permissions (600)
`Could not resolve hostname`	Name not found. Use the number, or turn Tailscale on
`Connection timed out`	Server off, asleep, wrong network, or firewall
`Connection refused`	SSH isn't running: `sudo systemctl start ssh`
`REMOTE HOST IDENTIFICATION HAS CHANGED`	After a reinstall: `ssh-keygen -R homeserver.local`
`bind: Address already in use`	An old tunnel is still open. Close it
`administratively prohibited`	The server doesn't allow tunnels: check `AllowTcpForwarding`