How to fix /home/user/.ssh/config: terminating, X bad configuration options in SSH

Run this command to see which line has the bad option:

ssh -G hostname

or for sshd config:

sudo sshd -t

The output will specify the exact line number and option name causing the issue.

SSH config options are case-sensitive. Common misspellings:
- 'identifyfile' should be 'IdentityFile'
- 'identitiesonly' should be 'IdentitiesOnly'
- 'hostkey' should be 'HostKey'
- 'port' should be 'Port'

Open your ~/.ssh/config file and verify the exact spelling matches the OpenSSH documentation.

If you're using a shared config across Linux and macOS:

For UseKeychain (macOS only):

# Add IgnoreUnknown directive above the option
IgnoreUnknown UseKeychain
UseKeychain yes

This tells non-Apple SSH to ignore the option while macOS still uses it.

For other macOS-specific options, use the same pattern:

IgnoreUnknown AddKeysToAgent,UseKeychain
AddKeysToAgent yes
UseKeychain yes

Some options require a minimum OpenSSH version:

ssh -V

Common version requirements:
- 'ProxyJump' requires OpenSSH 7.3+
- 'PubkeyAcceptedAlgorithms' requires OpenSSH 7.8+
- 'Include' directive requires OpenSSH 7.3+

If your version is too old, either upgrade SSH or remove the unsupported option.

SSH config files must use UTF-8 encoding with Unix line endings (LF, not CRLF).

In Vim:

:set fileformat=unix    " Change CRLF to LF
:set nobomb             " Remove Byte Order Mark
:wq

On command line:

# Convert CRLF to LF
dos2unix ~/.ssh/config

# Or with sed
sed -i 's/\r$//' ~/.ssh/config

Check the OpenSSH release notes and comment out any deprecated options. Common ones:

# Deprecated in OpenSSH 7.0+ (use PubkeyAuthentication instead)
# RSAAuthentication yes

# Deprecated in OpenSSH 7.5+ (now the default)
# UsePrivilegeSeparation sandbox

# Deprecated in OpenSSH 7.4+
# GSSAPICleanupCredentials yes

You can find the current supported options with:

man ssh_config

After making changes, verify the syntax:

# For ~/.ssh/config
ssh -G hostname

# For /etc/ssh/sshd_config
sudo sshd -t

Both commands should exit with no output if the config is valid. Then test your connection:

ssh -v hostname    # Use -v for verbose output to debug further