How to fix unknown option -- in SSH

Review the exact command you're running and look for misspelled options:

# WRONG - typos in option
ssh -prot 22 [email protected]
ssh -kep ~/.ssh/id_rsa [email protected]

# CORRECT - proper option names
ssh -p 22 [email protected]
ssh -i ~/.ssh/id_rsa [email protected]

Common typos:
- -prot should be -p (port)
- -kep or -key should be -i (identity file)
- -usr should be -l (login username)
- -hosy should be understood as hostname (not an option)

SSH options must use a single dash (-), not double-dashes (--):

# WRONG - double-dashes not supported by ssh
ssh --port 22 [email protected]
ssh --identity ~/.ssh/id_rsa [email protected]

# CORRECT - single dash
ssh -p 22 [email protected]
ssh -i ~/.ssh/id_rsa [email protected]

SSH does not support GNU-style long options. Some tools support both -p and --port, but SSH only accepts the short form.

Check what options are available in your SSH version:

ssh --help

Or view the full manual:

man ssh

Look for your option in the list. If it doesn't appear, either:
1. You have a typo
2. The option doesn't exist in your SSH version
3. You're using the wrong command (scp, sftp, ssh-keygen, etc.)

Some SSH options are only available in newer versions of OpenSSH. Check your version:

ssh -V

If you're trying to use an option that requires a newer version:
- Upgrade OpenSSH if possible
- Or use the -o option with the older equivalent:

# Instead of: ssh -J jumphost user@target
# On older SSH: ssh -o ProxyCommand="ssh -W %h:%p jumphost" user@target

Different SSH tools use different options. A common mistake:

# WRONG - scp uses -P (capital) for port, not -p
ssh -P 2222 [email protected]
scp -p file.txt [email protected]  # -p means preserve permissions

# CORRECT - ssh uses -p (lowercase) for port
ssh -p 2222 [email protected]

# CORRECT - scp uses -P (capital) for port
scp -P 2222 file.txt [email protected]

Remember:
- ssh uses lowercase -p for port
- scp and sftp use uppercase -P for port

If you're connecting without explicit options, check your config files:

cat ~/.ssh/config
cat /etc/ssh/ssh_config

Remove any deprecated or invalid options. Example:

# BAD - unknown options
Host myhost
  Hostname host.example.com
  User ubuntu
  IdentityFile ~/.ssh/id_rsa
  UnknownOption value

# GOOD - only valid options
Host myhost
  Hostname host.example.com
  User ubuntu
  IdentityFile ~/.ssh/id_rsa
  Port 22
  StrictHostKeyChecking accept-new

If you need to pass options that might not be recognized, use the -o flag to test:

# -o allows passing options in config file format
ssh -o "Port=2222" [email protected]
ssh -o "IdentityFile=~/.ssh/id_rsa" [email protected]

# Multiple -o flags work too
ssh -o "Port=2222" -o "StrictHostKeyChecking=no" [email protected]

This way, if the option is invalid, you get a clearer error message from the config parser rather than the command-line parser.