Errors and exceptions

A command can fail because tmux rejects it, or because the transport stops before returning a reply. Inspect the reported error and delivery state before retrying a mutation: tmux may already have received it.

For lookup failures caused by zero or multiple matches, see Filtering and queries.

A failed command, as a value¶

Fallible operations return expected<T, CommandFailure>. SCommandFailure records the failure kind, delivery status, exit code, and diagnostic.

Is it safe to retry?¶

Retry a mutation automatically only when you know it was not dispatched, or when repeating it is safe for your operation. A timeout, cancellation, or dropped connection can occur after tmux has acted. These APIs expose delivery information:

EDeliveryStatus distinguishes knot_started, kwritten, kreplied, and kindeterminate.

auto result = session.new_window({.name = "build"});
if (!result.has_value() && result.error().delivery == libtmux::DeliveryStatus::not_started) {
  // safe to retry
}

Treat unknown delivery as potentially executed.

A not_started result means the request did not reach tmux. A written result means the transport accepted the request but no terminal reply arrived.

For subprocess calls that complete normally, inspect the exit status. If a call is interrupted or times out without a delivery state, check tmux’s resulting state before repeating a mutation.