Signal Handling

Describing Signals for the Master Process

• QUIT: Quick shutdown

• TERM: Graceful shutdown

  • Waits for workers to finish their current requests

• HUP: Reloads the configuration

  • Starts the new worker processes with a new configuration
  • Then, gracefully shuts down older workers
  • If the application is not preloaded, then Gunicorn will also load the new version of it
• TTIN: Increment the number of processes by one
• TTOU: Decrement the number of processes by one
• USR1: Reopens the log files

• USR2: Upgrades Gunicorn on the fly

  • This gracefully shuts down old master processes
• WINCH: Gracefully shuts down the worker processes when Gunicorn is daemonized

Describing Signals for the Worker Process

• Typically, sending signals to the workers is unnecessary
• If the master process is running, any exited worker will be automatically respawned

• The following are valid signals:

  • QUIT: Quick shutdown
  • TERM: Graceful shutdown
  • USR1: Reopen the log files

Reloading the Configuration

• The HUP signal is used to reload Gunicorn configuration
• An example looks like:

2013-06-29 [20682] [INFO] Handling signal: hup
2013-06-29 [20682] [INFO] Hang up: Master
2013-06-29 [20703] [INFO] Booting worker with pid: 20703
2013-06-29 [20702] [INFO] Booting worker with pid: 20702
2013-06-29 [20688] [INFO] Worker exiting (pid: 20688)
2013-06-29 [20687] [INFO] Worker exiting (pid: 20687)
2013-06-29 [20689] [INFO] Worker exiting (pid: 20689)
2013-06-29 [20704] [INFO] Booting worker with pid: 20704

• Sending a HUP signal will:

  • Reload the configuration
  • Start the new worker processes
  • Gracefully shutdown older workers

References

• Signal Handling