phacility/phabricator · error · Exception

Unknown Mercurial command "%s"!

Error message

Unknown Mercurial command "%s"!

What it means

When Phabricator serves Mercurial over its SSH protocol endpoint, DiffusionMercurialWireProtocol keeps a fixed table of the wire commands it understands (between, branchmap, heads, hello, known, listkeys, lookup, pushkey, protocaps, stream_out, unbundle, ...). A client sending a command outside this table gets a hard 'Unknown Mercurial command' Exception before anything executes, because Phabricator must classify every wire command as read-only or mutating before serving it.

Source

Thrown at src/applications/diffusion/protocol/DiffusionMercurialWireProtocol.php:32

      'branches' => array('nodes'),
      'capabilities' => array(),
      'changegroup' => array('roots'),
      'changegroupsubset' => array('bases heads'),
      'debugwireargs' => array('one two *'),
      'getbundle' => array('*'),
      'heads' => array(),
      'hello' => array(),
      'known' => array('nodes', '*'),
      'listkeys' => array('namespace'),
      'lookup' => array('key'),
      'pushkey' => array('namespace', 'key', 'old', 'new'),
      'protocaps' => array('caps'),
      'stream_out' => array(''),
      'unbundle' => array('heads'),
    );

    if (!isset($commands[$command])) {
      throw new Exception(
        pht(
          'Unknown Mercurial command "%s"!',
          $command));
    }

    return $commands[$command];
  }

  public static function isReadOnlyCommand($command) {
    $read_only = array(
      'between' => true,
      'branchmap' => true,
      'branches' => true,
      'capabilities' => true,
      'changegroup' => true,
      'changegroupsubset' => true,
      'debugwireargs' => true,
      'getbundle' => true,

View on GitHub (pinned to 5720a38cfe)

Solutions

1. Use a Mercurial client version compatible with your Phabricator release (inspect the command table in src/applications/diffusion/protocol/DiffusionMercurialWireProtocol.php)
2. Update Phabricator: newer releases extend the command table as Mercurial evolves
3. Verify the client is speaking to the correct protocol endpoint (hg vs git vs svn) for the repository type

// server-side: check command membership before dispatch
$known = array('between','branchmap','heads','hello','known','listkeys','lookup','pushkey','protocaps','stream_out','unbundle');
if (!in_array($command, $known, true)) {
  // return a clean protocol error to the client instead of an unhandled throw
}

function isKnownMercurialWireCommand($cmd) {
  return in_array($cmd, array('between','branchmap','heads','hello','known','listkeys','lookup','pushkey','protocaps','stream_out','unbundle'), true);
}

try {
  $result = DiffusionMercurialWireProtocol::isReadOnlyCommand($command);
} catch (Exception $ex) {
  // reply with a formatted protocol error and close the session; a bad command must not kill the ssh daemon
}

When it happens

Trigger: An hg client (or raw protocol script) sends a wire command missing from the table: a newer Mercurial emitting a capability command this Phabricator release never listed, a script speaking the ssh:// protocol with a typo'd command, or a non-Mercurial client or scanner sending garbage to the endpoint.

Common situations: Client hg version newer than the Phabricator release; connecting with git tooling to an hg endpoint; automated probes or health checks hitting the Mercurial ssh service with junk.

Related errors

• This public key is already associated with another user or d
• Analyzing or decrypting SSH keys requires the "ssh-keygen" b
• A passphrase was provided for this private key, but it does
• This private key is not formatted correctly. Check that you
• This private key requires a passphrase, but the wrong passph

AI-assisted analysis of phacility/phabricator@5720a38cfe (2026-08-21). Data as JSON: /api/errors/efef96a92bfa2ef1. Report an issue: GitHub.