networking – Ubuntu transmits TTL 0 multicast packets

IP packets with TTL 0 shall not leave host.

But when I start application which multicasts UDP packets with TTL 0, I see packets with TTL 0 leaving host for few seconds, and coming to normal behavior of TTL 0. This most likely happens after reboot and first start of application.

I confirmed packets with TTL 0 leaving host with tcpdump:

05:31:39.048304 IP (tos 0x0, id 14487, offset 0, flags (DF), proto UDP (17), length 1344) > UDP, length 1316
05:31:39.049594 IP (tos 0x0, id 14488, offset 0, flags (DF), proto UDP (17), length 1344) > UDP, length 1316
05:31:39.051601 IP (tos 0x0, id 14489, offset 0, flags (DF), proto UDP (17), length 1344) > UDP, length 1316
05:31:39.053584 IP (tos 0x0, id 14490, offset 0, flags (DF), proto UDP (17), length 1344) > UDP, length 1316

As we can see ttl is not displayed which means TTL 0, as confirmed from tcpdump man page: (search ttl, it clearly indicated: ttl is the time-to-live; it is not reported if it is zero).

There are no any iptables rules running.

uname -a: Linux mydevice 4.15.0-101-generic #102-Ubuntu SMP Mon May 11 10:07:26 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

lsb_release -a:

No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 18.04.4 LTS
Release:        18.04
Codename:       bionic

What can be the cause for this behavior, and how can I resolve this?

node.js – Redis node to listen to SET events and set a TTL for each request

In my Nodejs app, I have to listen to and set every request that creates / updates a document TTL for this. For that I have to listen to everyone set Event and insert ttl on each document (whether it already exists or not).

I have my main Redis client (which adds documents to the Redis database):

const redisClient = createClient({
    url: redisUrl,
    tls: {
        ca: Buffer.from(redisCertBase64, 'base64').toString('utf-8'),

And I added another client that should be listening set Events:

const subscriberRedis = redisClient.duplicate()

function done(err) {
    logger.error('Notifications not active')
    if (err) {
        logger.error(err.stack || err.message || err)

const eventType = 'notify-keyspace-events'

subscriberRedis.config('get', eventType, (err, conf) => {
    if (err) {
        logger.debug('subscriberRedis:get =>', err.message)
        return done(err)
    logger.debug('conf =>', conf)
    if (conf(1).indexOf('EKx') < 0) {
        subscriberRedis.config('set', eventType, conf(1) + 'EKx', function (err) {
            if (err) {
                logger.debug('subscriberRedis:set =>', err.message)
                return done(err)

const EVENT_SET = '__keyevent@__:set'.replace('', config.get('REDIS.database'))      // EVENT_SET = __keyevent@0__:set

subscriberRedis.on('message', function (channel, key) {
    switch (channel) {
        case EVENT_SET:
  'Key "' + key + '" set!')


When I run this code, I get into the logs subscriberRedis:set => ERR only (P)SUBSCRIBE / (P)UNSUBSCRIBE / PING / QUIT allowed in this context which is logged by the subscriberRedis.config('set',...)

I'm not sure what I'm missing here.

Multithreading – How does ttl pro message work internally in rabbitmq?

What is the technology behind each message? How does the rabbit scale in this case?
It's almost like every message is attached to a timer task that is running at a certain time and a message is expiring. But when I think about it, a rabbit with ttl can have millions of messages, I'm sure that every message cannot have a thread assigned to it to expire. I could imagine that queue / map would be created per second and all messages belonging to this timestamp would expire with a continuously running thread. But one of these approaches doesn't seem scalable to me. It's almost a problem to downsize the scheduler.
Does anyone know how Rabbitmq or similar services like aws trigger do it?

Can I use another brand of RF TTL speedlite with another brand of RF Flash Trigger?

I've been doing photography and videography for a while, but I've always used the flash on my camera and thrown the light on the subject.

However, I recently planned to go wireless and bought a pair of apkina wireless transmitters and receivers. This works great, but in different lighting conditions or angles, I manually adjusted the settings on my Speedlite because it is connected to the modifier and not on my camera body.

I have a Shanny SN586-RF Speedlite that supports HSS, and although I am wireless, the Speedlite is not synchronized with my shutter, so the HSS does not work.

I decided to buy an RF flash trigger so that I can synchronize my camera with the flash and control my flash remotely. My options for the RF trigger are (Godox XPro TTL, Godox X2T-C E-TTL II, X1T-C, YONGNUO YN560-TX PRO, Shanny SN-E3-RTs).

Please advise…..

Flash – What are the facts about alleged problems with Godox TTL modes outside the camera with f-stops larger than 1: 4 with Sony DSLMs?

For example, an answer to Can a Godox XPro transmitter for one brand trigger a legacy flash for another brand + X1R in TTL? mentioned problems as described in the title.

A quick web search seems to provide contradicting and confusing statements. Therefore, it would be helpful if someone who knew the facts could document them. How will this system behave even with (e.g. adapted) lenses that are factually 1: 3.5 or wider but do not report this aperture electronically?

canon – Can a Godox XPro transmitter for one brand trigger an older flash for another brand + X1R in TTL?

No. While the X1R-C and XPro-S are compatible in terms of firepower and M-Power Control, the Godox X1R receivers do Not Carry out cross-brand TTL Just like the built-in radio transceivers of the Godox TTL flash units (TT685, V860II, V1).

For example, if you buy a Godox TT685-C and check whether the firmware version is 3.1 or higher, you can use it as a radio slave in TTL with the XPro-S outside the camera. This way I use an XPro-C on my 5DMkII, an XPro-F on my Fuji X100T and an Xpro-O on my Panasonic GX7.

However, if you have switched completely to Sony, it makes more sense to exchange your 600EX-RT for a TT685-S, a V860II-S or a V1-S so that you can use a flash with TTL / HSS camera and off-camera , Note that Godox and Sony have a known bug where TTL is underexposed when using an aperture greater than 1: 4. So if you're sticking to M, for example, using super cheap single-pole TT600S flashes for $ 60, this might be another option to consider.

Alternatively, you cannot use Godox as a trigger system. Cactus' V6II transceivers can run cross-brand TTL in their X-TTL system.

Can I use a XPro-S on a Sony a7riv to fire a Canon 600EX-RT that is mounted on an X1R-C in TTL mode, if so, how?

I recently switched from Canon to Sony and would like to fire my Canon flash (600EX-RT) mounted on an X1R-C while using an XPro-S camera.

I can successfully use this combination in manual mode, but in TTL mode, when the flash fires, not enough light is generated to illuminate the scene. Regardless of the compensation factor used, the light output remains constant. The same flash and X1R-C used in a Canon camera with an XPro-C work properly.

My question is, is an XPro-S compatible with an X1R-C? If they are compatible with the settings, the cooperation is of course very gratefully accepted.

Why is a Neewer flash underexposed on a Canon camera in TTL mode?

I'm starting to do flash photography and buy a simple flash to try it out.
In ETTL mode, strange behavior occurs when bouncing off the ceiling.

Camera: EOS 1300D
Flash: Neewer 562c

All pictures with 1/60 F9.0 ISO: 800

Without flash:

1/60 F9.0 ISO 800

So I turn on the flash, put it on ETTL, point it straight forward and get:
1/60 F9.0 ISO 800 ETTL Flash

I try to aim the flash straight up to deflect the light from my white ceiling and get the following:
1/60 F9.0 ISO 800 ETTL Flash points upwards

I have no idea how this bar is created with the unusual exposure above.

If I then set the flash to manual at 1/16 and still point upwards, I get an appropriate picture:

Enter image description here

Any ideas much appreciated.

fujifilm – HSS and TTL do not work with Fuji X-Pro2 and Godox system

I own a Fuji X-Pro2 camera. I recently purchased a Godox XPro-F shutter and a Godox SK400ii flash to try out some flash portrait shots.

I can easily get everything running at normal shutter speeds and in manual mode on the flash / shutter release. However, if I switch to the trigger's TTL mode, things will not work as I would have expected. I'm not sure how big the problem currently is in ignorance or user errors … Here are the problems I'm encountering right now:

  1. In TTL mode of the shutter, adjusting the exposure does not change the output. When I set the TTL mode, the flash output goes to 0 and the flash does not fire. It does not matter which settings I change at this point on the shutter or on the camera, the flash does not matter. I can adjust the power of the flash, but that eliminates the TTL point, right?
  2. When I set up the camera and trigger for using HSS in TTL and M modes, everything works fine for> 1/250 seconds. If I shift the shutter speed to 1/250, the flash stops firing. It fires again when I change the camera's sync mode to front or rear sync instead of FP. But if I am back on FP, it will be stopped.

Any ideas? I've reviewed a number of forums and YouTube videos at this point and I'm not sure what I'm doing wrong … Thanks for the help!

archive – MongoDB – Can I create a TTL index using the Rolling method?

I'm stuck with archiving a large amount of data in MongoDB 3.6

I want to delete 56 crore records in a collection. I tried to remove it by using bulk.remove (), but that's slow too (50 records are removed per second).

But somewhere I read, TTL index and scan interval every 1 hour. This will remove it faster.

However, if I create that index in the foreground, the collection will be locked. So I'm considering whether to work with the method for creating rolling indexes.

If so, for example, take a 3-node replica set, disconnect node 3, and then create an index. Once created, the data is automatically removed. Then, if I add the node back to the replica set, the primary node may be performing the deletion after I create the index. In the worst case, the data is already on this node and then on this remote does the replication break off?