The unix signal is a method of sending messages between processes. When a signal is sent, the operating system interrupts the target process's normal flow of execution. There are standard signals that are used to stop a process but there are also custom signals that can be used for other purposes. This document is an attempt to list all supported signals that Puma will respond to. In general, signals need only be sent to the master process of a cluster.
Sending Signals¶ ↑
If you are new to signals it can be useful to see how they can be used. When a process is created in a *nix like operating system it will have a PID - or process identifier that can be used to send signals to the process. For demonstration we will create an infinitely running process by tailing a file:
$ echo "foo" >> my.log $ irb > pid = Process.spawn 'tail -f my.log'
From here we can see that the tail process is running by using the
ps
command:
$ ps aux | grep tail schneems 87152 0.0 0.0 2432772 492 s032 S+ 12:46PM 0:00.00 tail -f my.log
You can send a signal in Ruby using the Process module:
$ irb > puts pid => 87152 Process.detach(pid) # http://ruby-doc.org/core-2.1.1/Process.html#method-c-detach Process.kill("TERM", pid)
Now you will see via ps
that there is no more
tail
process. Sometimes when referring to signals the
SIG
prefix will be used for instance SIGTERM
is
equivalent to sending TERM
via Process.kill
.
Puma Signals¶ ↑
Puma cluster responds to these signals:
-
TTIN
increment the worker count by 1 -
TTOU
decrement the worker count by 1 -
TERM
sendTERM
to worker. Worker will attempt to finish then exit. -
USR2
restart workers -
USR1
restart workers in phases, a rolling restart. -
HUP
reopen log files defined in stdout_redirect configuration parameter -
INT
equivalent of sending Ctrl-C to cluster. Will attempt to finish then exit. -
CHLD