2.2 Startup Sequence

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2.2.1 The sequence #

  1. The native socket. The runtime directory and the socket are created and given their modes and descriptors (§2.4). A failure to create the directory, set a mode, remove a stale socket file, bind, or make the listener nonblocking is fatal: resolvd logs native socket: <error> at error level and exits with status 1. A failure to write a descriptor is not fatal (§2.4).
  2. The stub listener. A UDP socket and then a TCP listener are bound to 127.0.0.53:53. A failure of either is fatal: resolvd logs stub listener on 127.0.0.53:53: <error> and exits with status 1.
  3. The registry. Machine\System\Network\Dns is read whole (§2.3). A missing or unreadable key is not an error; every value takes its default.
  4. The registry watch. A subtree watch is armed on Machine\System\Network (§2.3). If it cannot be armed, resolvd logs registry watch unavailable (<error>); configuration is read once and runs on the configuration it read in step 3 until it restarts.
  5. Query entropy. The engine is given a kernel-randomness provider. Every upstream transaction obtains fresh bytes through nonblocking getrandom; startup does not seed a userspace generator or read /dev/urandom. There is no clock fallback.
  6. The engine's inputs. The engine is given the kernel's hostname, the fallback servers and search domains, and the static names. A kernel hostname that is empty or (none) counts as no hostname.
  7. The control object is built from ControlSecurity (§5.2).
  8. netd. The first attempt to subscribe is made immediately (§3.1). Its failure is not fatal and is retried with backoff (§3.2).
  9. The listening line. resolvd logs listening on /run/resolvd/resolv.sock and 127.0.0.53:53 at info level.
  10. Readiness. READY=1 is sent (§2.1).
  11. The loop is entered (§2.5).

2.2.2 Answering from the moment of readiness #

Both doors are open, and answering, before readiness is reported, and neither waits for netd. A question asked the moment resolvd is ready is answered at once: synthetic and static names are answered, and anything that needs a server is answered unavailable until either a snapshot arrives or fallback servers are configured (§3.2).

2.2.3 Exiting #

resolvd has no shutdown path of its own. Apart from the startup failures above, nothing a client or an upstream server sends makes it exit.

2.2.3.1 Ending on a signal #

resolvd installs no signal handlers, so it ends when peinit signals it, with the default disposition, and leaves /run/resolvd/resolv.sock behind. The next start removes the stale socket file before binding (§2.4).

2.2.3.2 A poll failure exits #

When poll fails with anything other than EINTR, resolvd logs poll: <error> at error level and exits with status 1. EINTR is retried.

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