Starting an uWSGI server is the role of the system administrator, like starting the Web server. It should not be the role of the Web server to start the uWSGI server – though you can also do that if it fits your architecture.
How to best start uWSGI services at boot depends on the operating system you use.
On modern systems the following should hold true. On “classic” operating systems you can use init.d/rc.d scripts, or tools such as Supervisor, Daemontools or inetd/xinetd.
You can instruct uWSGI to write the master process PID to a file with the safe-pidfile option.
The uWSGI server responds to the following signals.
Signal
Description
Convenience command
SIGHUP
gracefully reload all the workers and the master process
--reload
SIGTERM
brutally reload all the workers and the master process
(use --die-on-term to respect the convention of shutting down the instance)
SIGINT
immediately kill the entire uWSGI stack
--stop
SIGQUIT
immediately kill the entire uWSGI stack
SIGUSR1
print statistics
SIGUSR2
print worker status or wakeup the spooler
SIGURG
restore a snapshot
SIGTSTP
pause/suspend/resume an instance
SIGWINCH
wakeup a worker blocked in a syscall (internal use)
SIGFPE
generate C traceback
SIGSEGV
generate C traceback
Note: there are better ways to manage your instances than signals, as an example the master-fifo is way more robust.
Reloading the server¶When running with the master process mode, the uWSGI server can be gracefully restarted without closing the main sockets.
This functionality allows you patch/upgrade the uWSGI server without closing the connection with the web server and losing a single request.
When you send the SIGHUP to the master process it will try to gracefully stop all the workers, waiting for the completion of any currently running requests.
Then it closes all the eventually opened file descriptors not related to uWSGI.
Lastly, it binary patches (using execve()) the uWSGI process image with a new one, inheriting all of the previous file descriptors.
The server will know that it is a reloaded instance and will skip all the sockets initialization, reusing the previous ones.
Note
Sending the SIGTERM signal will obtain the same result reload-wise but will not wait for the completion of running requests.
There are several ways to make uWSGI gracefully restart.
# using kill to send the signal kill -HUP `cat /tmp/project-master.pid` # or the convenience option --reload uwsgi --reload /tmp/project-master.pid # or if uwsgi was started with touch-reload=/tmp/somefile touch /tmp/somefile
Or from your application, in Python:
Or in Ruby,
Stopping the server¶If you have the uWSGI process running in the foreground for some reason, you can just hit CTRL+C to kill it off.
When dealing with background processes, you’ll need to use the master pidfile again. The SIGINT signal will kill uWSGI.
kill -INT `cat /tmp/project-master.pid` # or for convenience... uwsgi --stop /tmp/project-master.pid
If you’re running uwsgi in docker and you stop the container, docker sends a SIGTERM, which results in the action described in the table above. If you want the docker shutdown to gracefully stop uwsgi you should read over https://github.com/unbit/uwsgi/issues/849#issuecomment-118869386
The Master FIFO¶Starting from uWSGI 1.9.17, a new management system has been added using unix named pipes (fifo): The Master FIFO
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