# engine.DaemonGuard

- **Module:** engine
- **Package:** @libtmux/libtmux
- **Language:** TypeScript
- **Kind:** typealias
- **Source:** https://github.com/libtmux/libtmux-ts/blob/2cb93308200da38a26b59876618116850f110607/packages/libtmux/src/engine.ts#L55
- **Page:** https://libtmux.org/reference/ts/engine-daemonguard/

Making a command refuse to run on a daemon that is not the one it was read from.

A tmux id is unique within one daemon and reissued by the next: `kill-server`
and a restart give a new daemon the same socket, and it numbers its panes from
`%0` again. A handle captured before the restart therefore names something
that exists, belongs to somebody else, and answers to the same command.

Checking first and sending second does not close that: the daemon can change
between the two. `if-shell -F` does, because it is not a shell — tmux expands
the format inside its command queue and `cmdq_insert_after`s the guarded
command into the same queue, so nothing runs in between. The condition is
`pid` and `start_time` together, since pids are reused.

The refusal has to be visible. tmux answers a false condition with no output
and status 0, which is indistinguishable from a command that printed nothing,
so the else branch is a freshly named unknown command. A 128-bit suffix makes
matching a pre-existing command alias a guess, and the exact diagnostic
distinguishes the refusal from the guarded command failing. The guarded
command keeps its own stdout and stderr either way.