Issue 1:
Reproducible example

Install Celery 4.4.7:

python3 -m pip install -U 'celery[redis]==4.4.7'

Start Redis on 6395:

redis-server --daemonize yes --port 6395

Create celeryfoo.py:

import time
from celery import Celery

celery = Celery("hi")

redis_host = "redis://127.0.0.1:6395/0"
celery.conf.broker_url = redis_host
celery.conf.result_backend = redis_host
celery.conf.beat_schedule = {
"update-foo": {
"task": 'celeryfoo.update',
"schedule": 15,
"args": (1, 2, 3)
},
}
celery.conf.worker_redirect_stdouts = False
celery.conf.worker_log_color = False

@celery.task
def update(a, b, c):
with open("foo.log", "a") as f:
f.write(str(time.time()) + "\n")
return a, b, c

Start celery worker:

celery --no-color -A celeryfoo:celery worker --detach -l DEBUG --logfile celery.log

Check tail -f celery.log:

[2020-09-28 11:01:51,908: ERROR/MainProcess] consumer: Cannot connect to amqp://guest:**@127.0.0.1:5672//: [Errno 61] Connection refused.
Trying again in 32.00 seconds... (16/100)

[2020-09-28 11:02:24,029: ERROR/MainProcess] consumer: Cannot connect to amqp://guest:**@127.0.0.1:5672//: [Errno 61] Connection refused.
Trying again in 32.00 seconds... (16/100)

[2020-09-28 11:02:56,118: ERROR/MainProcess] consumer: Cannot connect to amqp://guest:**@127.0.0.1:5672//: [Errno 61] Connection refused.
Trying again in 32.00 seconds... (16/100)

[2020-09-28 11:03:28,221: ERROR/MainProcess] consumer: Cannot connect to amqp://guest:**@127.0.0.1:5672//: [Errno 61] Connection refused.
Trying again in 32.00 seconds... (16/100)

Mandatory Debugging Information

$ sw_vers
ProductName:	Mac OS X
ProductVersion:	10.15.7
BuildVersion:	19H2
$ redis-cli -p 6395 PING
PONG
$ celery --version
4.4.7 (cliffs)
$ python3 --version
Python 3.8.5

Issue 2:
Hi have an application running with Celery 4.4.2 with the following Daemonizing code:

/etc/default/my_celery_service

# Names of nodes to start
# most people will only start one node:
CELERYD_NODES="worker1"
# but you can also start multiple and configure settings
# for each in CELERYD_OPTS
#CELERYD_NODES="worker1 worker2 worker3"
# alternatively, you can specify the number of nodes to start:
#CELERYD_NODES=10

# Absolute or relative path to the 'celery' command:
CELERY_BIN="/opt/climmob_env/bin/celery"
#CELERY_BIN="/virtualenvs/def/bin/celery"

# App instance to use
# comment out this line if you don't use an app
#CELERY_APP="proj"
# or fully qualified:
CELERY_APP="climmob.config.celery_app"

# Where to chdir at start.
CELERYD_CHDIR="/opt/climmob/"

# Extra command-line arguments to the worker
CELERYD_OPTS="--time-limit=300 --concurrency=8"
# Configure node-specific settings by appending node name to arguments:
#CELERYD_OPTS="--time-limit=300 -c 8 -c:worker2 4 -c:worker3 2 -Ofair:worker1"

# Set logging level to DEBUG
#CELERYD_LOG_LEVEL="DEBUG"

# %n will be replaced with the first part of the nodename.
CELERYD_LOG_FILE="/opt/climmob_celery/log/%n%I.log"
CELERYD_PID_FILE="/opt/climmob_celery/run/%n.pid"

# Workers should run as an unprivileged user.
# You need to create this user manually (or you can choose
# a user/group combination that already exists (e.g., nobody).
CELERYD_USER="root"
CELERYD_GROUP="root"

# If enabled pid and log directories will be created if missing,
# and owned by the userid/group configured.
CELERY_CREATE_DIRS=1

/etc/init.d/my_celery_service

#!/bin/sh -e
# ============================================
# celeryd - Starts the Celery worker daemon.
# ============================================
#
# :Usage: /etc/init.d/celeryd {start|stop|force-reload|restart|try-restart|status}
# :Configuration file: /etc/default/celeryd (or /usr/local/etc/celeryd on BSD)
#
# See http://docs.celeryproject.org/en/latest/userguide/daemonizing.html#generic-init-scripts

### BEGIN INIT INFO
# Provides: celeryd
# Required-Start: $network $local_fs $remote_fs
# Required-Stop: $network $local_fs $remote_fs
# Default-Start: 2 3 4 5
# Default-Stop: 0 1 6
# Short-Description: celery task worker daemon
### END INIT INFO
#
#
# To implement separate init-scripts, copy this script and give it a different
# name. That is, if your new application named "little-worker" needs an init,
# you should use:
#
# cp /etc/init.d/celeryd /etc/init.d/little-worker
#
# You can then configure this by manipulating /etc/default/little-worker.
#
VERSION=10.1
echo "celery init v${VERSION}."
if [ $(id -u) -ne 0 ]; then
echo "Error: This program can only be used by the root user."
echo " Unprivileged users must use the 'celery multi' utility, "
echo " or 'celery worker --detach'."
exit 1
fi

origin_is_runlevel_dir () {
set +e
dirname $0 | grep -q "/etc/rc.\.d"
echo $?
}

# Can be a runlevel symlink (e.g., S02celeryd)
if [ $(origin_is_runlevel_dir) -eq 0 ]; then
SCRIPT_FILE=$(readlink "$0")
else
SCRIPT_FILE="$0"
fi
SCRIPT_NAME="$(basename "$SCRIPT_FILE")"

DEFAULT_USER="celery"
DEFAULT_PID_FILE="/var/run/celery/%n.pid"
DEFAULT_LOG_FILE="/var/log/celery/%n%I.log"
DEFAULT_LOG_LEVEL="INFO"
DEFAULT_NODES="celery"
DEFAULT_CELERYD="-m celery worker --detach"

if [ -d "/etc/default" ]; then
CELERY_CONFIG_DIR="/etc/default"
else
CELERY_CONFIG_DIR="/usr/local/etc"
fi

CELERY_DEFAULTS=${CELERY_DEFAULTS:-"$CELERY_CONFIG_DIR/${SCRIPT_NAME}"}

# Make sure executable configuration script is owned by root
_config_sanity() {
local path="$1"
local owner=$(ls -ld "$path" | awk '{print $3}')
local iwgrp=$(ls -ld "$path" | cut -b 6)
local iwoth=$(ls -ld "$path" | cut -b 9)

if [ "$(id -u $owner)" != "0" ]; then
echo "Error: Config script '$path' must be owned by root!"
echo
echo "Resolution:"
echo "Review the file carefully, and make sure it hasn't been "
echo "modified with mailicious intent. When sure the "
echo "script is safe to execute with superuser privileges "
echo "you can change ownership of the script:"
echo " $ sudo chown root '$path'"
exit 1
fi

if [ "$iwoth" != "-" ]; then # S_IWOTH
echo "Error: Config script '$path' cannot be writable by others!"
echo
echo "Resolution:"
echo "Review the file carefully, and make sure it hasn't been "
echo "modified with malicious intent. When sure the "
echo "script is safe to execute with superuser privileges "
echo "you can change the scripts permissions:"
echo " $ sudo chmod 640 '$path'"
exit 1
fi
if [ "$iwgrp" != "-" ]; then # S_IWGRP
echo "Error: Config script '$path' cannot be writable by group!"
echo
echo "Resolution:"
echo "Review the file carefully, and make sure it hasn't been "
echo "modified with malicious intent. When sure the "
echo "script is safe to execute with superuser privileges "
echo "you can change the scripts permissions:"
echo " $ sudo chmod 640 '$path'"
exit 1
fi
}

if [ -f "$CELERY_DEFAULTS" ]; then
_config_sanity "$CELERY_DEFAULTS"
echo "Using config script: $CELERY_DEFAULTS"
. "$CELERY_DEFAULTS"
fi

# Sets --app argument for CELERY_BIN
CELERY_APP_ARG=""
if [ ! -z "$CELERY_APP" ]; then
CELERY_APP_ARG="--app=$CELERY_APP"
fi

# Options to su
# can be used to enable login shell (CELERYD_SU_ARGS="-l"),
# or even to use start-stop-daemon instead of su.
CELERYD_SU=${CELERY_SU:-"su"}
CELERYD_SU_ARGS=${CELERYD_SU_ARGS:-"-s /bin/bash"}

CELERYD_USER=${CELERYD_USER:-$DEFAULT_USER}

# Set CELERY_CREATE_DIRS to always create log/pid dirs.
CELERY_CREATE_DIRS=${CELERY_CREATE_DIRS:-0}
CELERY_CREATE_RUNDIR=$CELERY_CREATE_DIRS
CELERY_CREATE_LOGDIR=$CELERY_CREATE_DIRS
if [ -z "$CELERYD_PID_FILE" ]; then
CELERYD_PID_FILE="$DEFAULT_PID_FILE"
CELERY_CREATE_RUNDIR=1
fi
if [ -z "$CELERYD_LOG_FILE" ]; then
CELERYD_LOG_FILE="$DEFAULT_LOG_FILE"
CELERY_CREATE_LOGDIR=1
fi

CELERYD_LOG_LEVEL=${CELERYD_LOG_LEVEL:-${CELERYD_LOGLEVEL:-$DEFAULT_LOG_LEVEL}}
CELERY_BIN=${CELERY_BIN:-"celery"}
CELERYD_MULTI=${CELERYD_MULTI:-"$CELERY_BIN multi"}
CELERYD_NODES=${CELERYD_NODES:-$DEFAULT_NODES}

export CELERY_LOADER

if [ -n "$2" ]; then
CELERYD_OPTS="$CELERYD_OPTS $2"
fi

CELERYD_LOG_DIR=`dirname $CELERYD_LOG_FILE`
CELERYD_PID_DIR=`dirname $CELERYD_PID_FILE`

# Extra start-stop-daemon options, like user/group.
if [ -n "$CELERYD_CHDIR" ]; then
DAEMON_OPTS="$DAEMON_OPTS --workdir=$CELERYD_CHDIR"
fi

check_dev_null() {
if [ ! -c /dev/null ]; then
echo "/dev/null is not a character device!"
exit 75 # EX_TEMPFAIL
fi
}

maybe_die() {
if [ $? -ne 0 ]; then
echo "Exiting: $* (errno $?)"
exit 77 # EX_NOPERM
fi
}

create_default_dir() {
if [ ! -d "$1" ]; then
echo "- Creating default directory: '$1'"
mkdir -p "$1"
maybe_die "Couldn't create directory $1"
echo "- Changing permissions of '$1' to 02755"
chmod 02755 "$1"
maybe_die "Couldn't change permissions for $1"
if [ -n "$CELERYD_USER" ]; then
echo "- Changing owner of '$1' to '$CELERYD_USER'"
chown "$CELERYD_USER" "$1"
maybe_die "Couldn't change owner of $1"
fi
if [ -n "$CELERYD_GROUP" ]; then
echo "- Changing group of '$1' to '$CELERYD_GROUP'"
chgrp "$CELERYD_GROUP" "$1"
maybe_die "Couldn't change group of $1"
fi
fi
}

check_paths() {
if [ $CELERY_CREATE_LOGDIR -eq 1 ]; then
create_default_dir "$CELERYD_LOG_DIR"
fi
if [ $CELERY_CREATE_RUNDIR -eq 1 ]; then
create_default_dir "$CELERYD_PID_DIR"
fi
}

create_paths() {
create_default_dir "$CELERYD_LOG_DIR"
create_default_dir "$CELERYD_PID_DIR"
}

export PATH="${PATH:+$PATH:}/usr/sbin:/sbin"

_get_pidfiles () {
# note: multi < 3.1.14 output to stderr, not stdout, hence the redirect.
${CELERYD_MULTI} expand "${CELERYD_PID_FILE}" ${CELERYD_NODES} 2>&1
}

_get_pids() {
found_pids=0
my_exitcode=0

for pidfile in $(_get_pidfiles); do
local pid=`cat "$pidfile"`
local cleaned_pid=`echo "$pid" | sed -e 's/[^0-9]//g'`
if [ -z "$pid" ] || [ "$cleaned_pid" != "$pid" ]; then
echo "bad pid file ($pidfile)"
one_failed=true
my_exitcode=1
else
found_pids=1
echo "$pid"
fi

if [ $found_pids -eq 0 ]; then
echo "${SCRIPT_NAME}: All nodes down"
exit $my_exitcode
fi
done
}

_chuid () {
${CELERYD_SU} ${CELERYD_SU_ARGS} "$CELERYD_USER" -c "$CELERYD_MULTI $*"
}

start_workers () {
if [ ! -z "$CELERYD_ULIMIT" ]; then
ulimit $CELERYD_ULIMIT
fi
_chuid $* start $CELERYD_NODES $DAEMON_OPTS \
--pidfile="$CELERYD_PID_FILE" \
--logfile="$CELERYD_LOG_FILE" \
--loglevel="$CELERYD_LOG_LEVEL" \
$CELERY_APP_ARG \
$CELERYD_OPTS
}

dryrun () {
(C_FAKEFORK=1 start_workers --verbose)
}

stop_workers () {
_chuid stopwait $CELERYD_NODES --pidfile="$CELERYD_PID_FILE"
}

restart_workers () {
_chuid restart $CELERYD_NODES $DAEMON_OPTS \
--pidfile="$CELERYD_PID_FILE" \
--logfile="$CELERYD_LOG_FILE" \
--loglevel="$CELERYD_LOG_LEVEL" \
$CELERY_APP_ARG \
$CELERYD_OPTS
}

kill_workers() {
_chuid kill $CELERYD_NODES --pidfile="$CELERYD_PID_FILE"
}

restart_workers_graceful () {
echo "WARNING: Use with caution in production"
echo "The workers will attempt to restart, but they may not be able to."
local worker_pids=
worker_pids=`_get_pids`
[ "$one_failed" ] && exit 1

for worker_pid in $worker_pids; do
local failed=
kill -HUP $worker_pid 2> /dev/null || failed=true
if [ "$failed" ]; then
echo "${SCRIPT_NAME} worker (pid $worker_pid) could not be restarted"
one_failed=true
else
echo "${SCRIPT_NAME} worker (pid $worker_pid) received SIGHUP"
fi
done

[ "$one_failed" ] && exit 1 || exit 0
}

check_status () {
my_exitcode=0
found_pids=0

local one_failed=
for pidfile in $(_get_pidfiles); do
if [ ! -r $pidfile ]; then
echo "${SCRIPT_NAME} down: no pidfiles found"
one_failed=true
break
fi

local node=`basename "$pidfile" .pid`
local pid=`cat "$pidfile"`
local cleaned_pid=`echo "$pid" | sed -e 's/[^0-9]//g'`
if [ -z "$pid" ] || [ "$cleaned_pid" != "$pid" ]; then
echo "bad pid file ($pidfile)"
one_failed=true
else
local failed=
kill -0 $pid 2> /dev/null || failed=true
if [ "$failed" ]; then
echo "${SCRIPT_NAME} (node $node) (pid $pid) is down, but pidfile exists!"
one_failed=true
else
echo "${SCRIPT_NAME} (node $node) (pid $pid) is up..."
fi
fi
done

[ "$one_failed" ] && exit 1 || exit 0
}

case "$1" in
start)
check_dev_null
check_paths
start_workers
;;

stop)
check_dev_null
check_paths
stop_workers
;;

reload|force-reload)
echo "Use restart"
;;

status)
check_status
;;

restart)
check_dev_null
check_paths
restart_workers
;;

graceful)
check_dev_null
restart_workers_graceful
;;

kill)
check_dev_null
kill_workers
;;

dryrun)
check_dev_null
dryrun
;;

try-restart)
check_dev_null
check_paths
restart_workers
;;

create-paths)
check_dev_null
create_paths
;;

check-paths)
check_dev_null
check_paths
;;

*)
echo "Usage: /etc/init.d/${SCRIPT_NAME} {start|stop|restart|graceful|kill|dryrun|create-paths}"
exit 64 # EX_USAGE
;;
esac

exit 0

Even my celery_app is the same.

celeryApp = Celery("clmtask", broker="redis://localhost:6379/0", backend="redis://localhost:6379/0")

But If I move to 4.4.7 the same code does not work with the following message:

[2020-08-17 09:41:22,546: ERROR/MainProcess] consumer: Cannot connect to amqp://guest:**@127.0.0.1:5672//: [Errno 111] Connection refused.

Trying again in 2.00 seconds... (1/100)

It seems that 4.4.7 is ignoring my broker and backend parameters or not reading properly CELERY_APP in /etc/default/my_celery_service