Daemon behavior - LXD documentation
Description: Introduction: This specification covers some of the daemon’s behavior, such as reaction to given signals, crashes, … Startup: On every start, LXD checks that its directory structure exists. If it d...

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# Daemon behavior

## Introduction

This specification covers some of the daemon’s behavior, such as reaction to given signals, crashes, …

## Startup

On every start, LXD checks that its directory structure exists. If it doesn’t, it’ll create the required directories, generate a key pair and initialize the database.

Once the daemon is ready for work, LXD will scan the instances table for any instance for which the stored power state differs from the current one. If an instance’s power state was recorded as running and the instance isn’t running, LXD will start it.

## Signal handling

### `SIGINT`, `SIGQUIT`, `SIGTERM`

For those signals, LXD assumes that it’s being temporarily stopped and will be restarted at a later time to continue handling the instances.

The instances will keep running and LXD will close all connections and exit cleanly.

### `SIGPWR`

Indicates to LXD that the host is going down.

LXD will attempt a clean shutdown of all the instances. After 30s, it will kill any remaining instance.

The instance `power_state` in the instances table is kept as it was so that LXD after the host is done rebooting can restore the instances as they were.

### `SIGUSR1`

Write a memory profile dump to the file specified with `--memprofile`.