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I am experiencing weird issue during last few weeks. Even official Apple support couldn't help me with this. And I don't know, where else to ask, so I am trying here...

Connections to some FTP servers have extremely slow read. Like I have to try 3-4 times to open the folder, because it crashes on timeout. And uploading files is even worse, I have to try it up to 10-20x to successfull upload.

And as I specified in the title - it seems it's just a read-speed. Because when it finally finish reading, download / upload has normal speed. I've found out when I was trying to upload a video. It took 3-4 mins to successfully start uploading, but then it was really fast.

It's strange that this happens only with few servers, the others works fine as usual. More strange that it started just like nothing. I didn't change any settings, anything.

I hope I could find there someone who could help me with this, because it's extremely annoying, especially when you need to debug online and after every small change, you have to try uploading for 5 minutes.

I've tried some recommended solutions, but nothing worked for me. There are some of them:

  • reinstalling FTP client
  • tried another FTP client
  • run Mac at safe mode
  • restart network adapter
  • reinstall system (not hard reinstall with formatting, just reinstall)

Please if you have ANY other way how to fix this, I will be incredibly grateful!

H Sturma
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1 Answers1

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I have the same issue on iMac using FileZilla (or Captain FTP, or Cyber duck, for the "Don't use FileZilla"-People ;) ).

I tried active mode, but still takes 1-3 Minutes to show the content of a folder, or to start the download/upload.

I figured, that it has something to do with the latest OSX Versions Big Sur 11.4, 11.5, 11.6

When I open the same ftp client and connect to the same server on my MacBook with OSX 10.12. High Sierra , everything works fine.

I found this article:

FTP clients (any) will hang on MLSD with passive mode in macOS Big Sur 11.4 and 11.5

They say "sysctl -w net.ipv4.tcp_tw_recycle=0" fixes the problem.

But the command doesn't really work on Big Sur, since tcp_tw_recycle has been removed...

Toto
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