Update the upgrade function - it captures the old PID before it's overwritten by the upgrade (ie USR2 signal), then kills it once the upgrade has succeeded

unicorn

#!/bin/sh
# forked from https://gist.github.com/ethier/7190310
# via http://uncorruptedstate.com/blog/2013/10/27/zero-downtime-deployment-with-rails-and-unicorn/

### Unicorn variables ###
TIMEOUT=${TIMEOUT-60}
APP_ROOT=/home/web/current
UNICORN=$APP_ROOT/bin/unicorn
TMP_PATH=$APP_ROOT/tmp
PID_PATH=$APP_ROOT/tmp/pids
PID=$PID_PATH/unicorn.pid
OLD_PID=$PID_PATH/unicorn.old.pid
RAILS_ENV=staging
USER=web
GROUP=pass

# See http://technology.customink.com/blog/2012/03/16/simple-garbage-collection-tuning-for-rails/
export RUBY_GC_MALLOC_LIMIT=60000000
export RUBY_GC_HEAP_INIT_SLOTS=1800000 # Slots Live + 20%
export RUBY_GC_HEAP_FREE_SLOTS=18000 # 1% of HEAP_MIN_SLOTS
export RUBY_HEAP_SLOTS_INCREMENT=144000 # 8% of HEAP_MIN_SLOTS
export RUBY_HEAP_SLOTS_GROWTH_FACTOR=1
export LD_PRELOAD=/usr/lib/libtcmalloc_minimal.so.0.1.0

CMD="$UNICORN -D -E $RAILS_ENV -c $APP_ROOT/config/unicorn.rb"

INIT_CONF=$APP_ROOT/config/unicorn.conf

action="$1"
set -u

test -f "$INIT_CONF" && . $INIT_CONF

cd $APP_ROOT || exit 1

sig () {
  test -s "$PID" && kill -$1 `cat $PID`
}

oldsig () {
  test -s $OLD_PID && kill -$1 `cat $OLD_PID`
}

workersig () {
  workerpid=$PID_PATH/worker.$2.pid
  test -s "$workerpid" && kill -$1 `cat $workerpid`
}

create_tmp_path () {
  test -d $TMP_PATH || ( mkdir -p $TMP_PATH && chown $USER $TMP_PATH )
}

create_pid_path () {
  test -d $PID_PATH || ( mkdir -p $PID_PATH && chown $USER $PID_PATH )
}

archive_pid () {
  rm -f $OLD_PID
  cp $PID $OLD_PID
}

case $action in
start)
  create_tmp_path
  create_pid_path
  sig 0 && echo >&2 "Already running" && exit 0
  $CMD
;;
stop)
  sig QUIT && exit 0
  echo >&2 "Not running"
;;
force-stop)
  sig TERM && exit 0
  echo >&2 "Not running"
;;
restart|reload)
  sig HUP && echo reloaded OK && exit 0
  echo >&2 "Couldn't reload, starting '$CMD' instead"
  $CMD
;;
upgrade)
  create_tmp_path
  create_pid_path
  archive_pid && sig USR2 && oldsig QUIT && exit 0
  echo >&2 "Couldn't upgrade, starting '$CMD' instead"
  $CMD
;;
status)
  sig 0 && echo "running with pid `cat $PID`" && exit 0
  echo stopped && exit 1
;;
kill_worker)
  workersig QUIT $2 && exit 0
  echo >&2 "Worker not running"
;;
reopen-logs)
  sig USR1
;;
*)
  echo >&2 "Usage: $0 <start|stop|status|restart|upgrade|status|force-stop|reopen-logs|kill_worker>"
  exit 1
;;
esac