## Bitcoin core – what prevents users from adding useless blocks to very old blocks to reset new transactions?

As I understand it, nodes on the network should accept the longest branch of blocks and ignore other branches (excuse my terminology if it's not used normally – I hope it's clear what I mean).

If this is correct, I wonder what would prevent me from creating my own node by appending blocks to very old blocks. For example, these attached blocks can include transactions from my address to another of my addresses (just to make sure that the block is valid – I assume there are some restrictions that make a block valid, such as the number of Transactions or bits in a block). After probably a long time, a branch that grew out of the current branch would have reversed all transactions from the block my node started with to the currently active block and replaced all of them with my useless transactions instead.

What is stopping me? I know I still have to mine these blocks and understand that this would probably be the main thing that prevents me from doing this now.

As far as I know, the difficulty of mining is determined by the number of blocks mined in a given period of time. Assume that one day the BTC network becomes unusable for some reason and almost no new blocks have been created. Would it then be possible to do this (after a long time to keep the difficulty of my own mined blocks low)?

Thanks for all the answers in advance. If BTC is ever going to be out of date and unused, it would be cool to magically delete everything (if there are still nodes nearby).

## Synaptic Package Manager is practically useless

Why is that still a problem?

E: The value & # 39; Stableold Stable & # 39; is invalid for APT :: Default-Release because such a release is not available in the sources
E: _cache-> open () failed, please report.

How can this be fixed? Synaptic Package Manager is practically useless.

## Woocommerce Useless Image Requests – WordPress Development Stack Exchange

My installation is WordPress 5.3.2, Woocommerce 3.8.1, StoreFront 2.5.3, no other plug-ins. I created a variable product with an image. When my browser goes to the product page, three images are requested:

• Body Renda-Grega manga Comprida-Capa.jpg
• Body-Renda-Grega-Manga-Comprida-Capa-416 × 312.jpg
• Body-Renda-Grega-Manga-Comprida-Capa-324 × 324.jpg

This appears to be very inefficient. It's the same picture. Why not just download the larger one and then rescale it using CSS for the two thumbnails? I can't get around it, my live site has thousands of pictures and that means many thousands of thumbnails not needed were created and lots of http requests and bandwidth. Speed ​​is crucial to turn visitors into customers. The most common bottleneck on an e-commerce website is the number of images and their size. To triple the number of requests and in this case to almost double the amount of data to be transferred without making a profit does not seem right.
Am I missing something here, is there a workaround? Thanks for your help.

## [ Politics ] Open question: is it okay to block users like Pearl L because their answers are useless?

Lol Pearl L really followed this question on both accounts because I blocked them

## Linux – Jupyter Hub simply says "not found" and nothing more and makes it useless

One of my teammates cloned an Ubuntu 16.04 server into 2 servers in Azure, and since then our Jupyter Hub has problems. When I connect to Jupyter Hub via http: // localhost: 8000 / (via an SSH tunnel), it simply finds "Not Found" and nothing in the browser.

I think we're using Jupyter Hub 1.0.0, but jupyterhub –version outputs this version-looking string and then a traceback. ISTR, which is considered harmless.

Checking / var / log with a recursive grep has not proven to be informative.

When I follow the process listening on tcp / 8000, I see:

(pid 30739) read(20, "GET / HTTP/1.1rnHost: localhost:8000rnConnection: keep-alivernPragma: no-cachernCache-Control: no-cachernUpgrade-Insecure-Requests: 1rnUser-Agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/78.0.3904.108 Safari/537.36rnSec-Fetch-User: ?1rnAccept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3rnSec-Fetch-Site: nonernSec-Fetch-Mode: navigaternAccept-Encoding: gzip, deflate, brrnAccept-Language: en-US,en;q=0.9rnrn", 65536) = 521
(pid 30739) write(1, "00:18:40.279 (ConfigProxy) 33(31merror33(39m: 404 GET / n", 55) = 55
(pid 30739) socket(PF_INET, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, IPPROTO_IP) = 22
(pid 30739) connect(22, {sa_family=AF_INET, sin_port=htons(8081), sin_addr=inet_addr("127.0.0.1")}, 16) = -1 EINPROGRESS (Operation now in progress)
(pid 30739) epoll_ctl(13, EPOLL_CTL_ADD, 22, {EPOLLOUT, {u32=22, u64=22}}) = 0
(pid 30739) epoll_wait(13, ({EPOLLOUT|EPOLLERR|EPOLLHUP, {u32=22, u64=22}}), 1024, 719) = 1
(pid 30739) getsockopt(22, SOL_SOCKET, SO_ERROR, (111), (4)) = 0
(pid 30739) epoll_ctl(13, EPOLL_CTL_DEL, 22, 0x7fffe88bc610) = 0
(pid 30739) close(22)                   = 0
(pid 30739) write(1, "00:18:40.281 (ConfigProxy) 33(31merror33(39m: Failed to get custom error page: Error: connect ECONNREFUSED 127.0.0.1:8081n    at TCPConnectWrap.afterConnect (as oncomplete) (net.js:1129:14) {n  errno: 'ECONNREFUSED',n  code: 'ECONNREFUSED',n  syscall: 'connect',n  address: '127.0.0.1',n  port: 8081n}n", 300) = 300
(pid 30739) writev(20, ({"HTTP/1.1 404 Not FoundrnDate: Wed, 11 Dec 2019 00:18:40 GMTrnConnection: keep-alivernTransfer-Encoding: chunkedrnrn9", 116}, {"rn", 2}, {"Not Found", 9}, {"rn", 2}, {"0rnrn", 5}), 5) = 134


I've been googling for services that would listen to tcp / 8081 (found nothing interesting), and I searched for 8081 in / etc / services (found tproxy) but did not find much. tproxy does not feel very relevant in a fast Google.

What is this mysterious service that Jupyter Hub wants to connect to, and how can I start it?

Or more generally, if the thing with tcp / 8081 is a red herring: how can I make Jupyter Hub happy again?

Thanks a lot!

## useless car pass

Good;
When I install my Ubuntu, I choose automatic login when I enter my username and password, but now I can not change or remove it at all.
I try it in recovery mode, change the root pass and so on. None of them worked and I can somehow log in, but it's impossible to change it.

## Useless production

Please note the following productions. How can I identify a useless production?

S->aS|A|C

A->a

B->aa

C->aCb


Zulfi.

## Your attack roll uses a Specific Weapon; If you use two weapons at the same time, use one weapon and then the other

The rules for the two-weapon fight are:

If you perform the action of attack and attack with a light melee weapon that you hold in your hand in one handYou can use a bonus action to attack with another light melee weapon you hold in your hand in the other hand. You will not add your ability modifier to the damage of the bonus attack unless this modifier is negative (…)

You must use two for this feature / feature (available for all characters) light Weapons and you attack each separately.

Suppose only one weapon is +1 and magic, then only the attack with this weapon would handle resistance to damage from non-magic attacks and only this weapon would get the +1 for his attack and damage rolls. Your next attack would be with the non-magic weapon and would not receive such benefits.

## However, a longsword is not an easy weapon

Note that long swords are not light weapons and therefore usually can not be used with two-weapon combat. The exception is when a character has the Dual Wielder talent, which says:

(…) You can fight with two weapons, even if the one-handed melee weapons you use are not easy (…)

Player's Handbook (Page 165)

If your character does not have this talent, there's little reason to lead two long swords at the same time, and you should almost certainly wear a shield or a two-handed weapon instead.

## Dungeons and Dragons – Am I just or is age in D & D more or less useless?

Thank you for giving a response to Roleplay Stack Exchange!

But avoid

• Make statements based on opinions; Cover them with references or personal experience.

Use MathJax to format equations. Mathjax reference.

## dnd 5e – is the metamagic option & # 39; wizard's advanced spell & # 39; for the magic & # 39; thaumaturgy & # 39; effectively useless?

The Thaumaturgy spell states

They manifest a small miracle, a sign of supernatural power within reach. You create one of the following magical effects within easy reach:

, Her voice is up to three times as loud as normal for 1 minute.
, They cause flames to flicker, lighten, darken or change color for 1 minute.
, They cause harmless tremors in the ground for 1 minute.
, You create an instant sound that emanates from a point of your choice in range, eg. A thunderbolt, the scream of a raven, or a threatening whisper.
, They immediately open an unlocked door or unlocked window or strike.
, They change the look of your eyes for 1 minute.

If you cast this spell multiple times, you can have up to three of them 1 minute effects You can reject such an effect as an action.

The metamagic feature "Wizard's Extended Spell" states:

If you cast a spell that lasts one minute or more, you can spend 1 spell to double its duration to a maximum of 24 hours.

Although the duration of Thaumaturgy 1 minute, the descriptions describe the effects as lasting only 1 minute instead of "for the duration of the spell." Does this mean that Expanded Spell has no meaningful effect? Thaumaturgy?