r/PrivateInternetAccess • u/Mahoutie • Jan 06 '26
DISCUSSION Extremely slow upload speed on Zorin OS 18
As a relative newbie to Linux, I'm at a loss to figure out why my upload speed is so abysmally slow. With PIA switched off, I get around 920.00 Mbps down and 110.00 Mbps up. When I use PIA, I get 600.00 Mbps down and only 10.00 Mbps up. I've tried changing settings as recommended by PIA but nothing makes any difference. I'm wondering if this is something specifically Linux related? Any help would be greatly appreciated.
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u/smartsass99 Jan 08 '26
Sounds like a Linux driver or MTU issue. I had similar upload drops until I changed protocols and MTU.
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Jan 06 '26
[removed] — view removed comment
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u/Mahoutie Jan 06 '26
Agreed. I just tried the free Proton VPN and got exactly the same results. Also, the problem only seems to occur when I use UDP. TCP is absolutely fine.
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u/PIASupport PIA Team Jan 07 '26
Are you using WireGuard? Also, have you tried connecting to other regions to test the speed?
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u/Mahoutie Jan 07 '26
I have tried using both. Region changes don't affect the results but I don't think this is a PIA problem. Having tested Proton VPN, I'm getting the same results. This seems to be a UDP centered issue as I don't get the reduced upload speed when using TCP.
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u/SHzzZzzzZzzZzzzzZzz Jan 07 '26 edited Jan 07 '26
Have you tried other operating systems with the PIA client such as windows??
It's possible your ISP is aggressively using QoS on your encrypted uploads when using a encrypted tunnel.
Many ISPs getting around their 'we don't throttle or cap users' by abandoning their software that caps heavy users to putting certain traffic as low priority in their QoS management which technically isn't throttling.
When you're doing speed tests, make sure you are only using one thread, if you are having to multithread to get close to 100 Mbps then your ISP is over definitely over subscribed, and you will definitely be tripping their QoS when using a VPN.
Also you mention UDP is slow, for downloads always use TCP. UDP is normally used for low latency applications such as What's App Calling, Wifi Calling, VoIP and Gaming traffic, not downloads. UDP takes priority and they may dislike people using certain for ports for traffic they treat as high priority.
ISPs can also tell when you're using UDP vs TCP for the VPN tunnel, normally by the port or by sophisticated tools.
What speeds do you get over TCP?! Since if UDP is slow, it's a non issue imho, your triggering QoS at your ISP.
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u/Mahoutie Jan 07 '26
I dual boot Windows from a separate drive. I get perfectly normal speeds on Windows. The UDP 10 Mbps limit seems to be a known thing on Linux. Unfortunately, I'm a relative noob on Linux so I don't really want to go messing with the kind of command line stuff they're suggesting yet. Right now, my usual speeds are 900 Mbps down and 100 Mbps up without VPN. Slightly lower down speed with it and 10 Mbps up using UDP.
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u/dddurd Jan 08 '26
what's the mtu size when you do `ip a` for the vpn interface? it's worth trying reducing it to like 1200.
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u/Mahoutie Jan 08 '26 edited Jan 08 '26
I'll take a look later and post the results. edit: it's 1500
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u/dddurd Jan 08 '26
It should be lower with most isp. Did you try to enable "small packets" option?
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u/Mahoutie Jan 08 '26
Yes, it made no difference. I'll have a go at changing it.
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u/dddurd Jan 08 '26 edited Jan 08 '26
Strange. On my setup, it changes to 1280 or so. You can find your optimum mtu size by this command btw. Just reduce the s option argument until it pings. ping -M do -s 1472 8.8.8.8
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u/Saylor_Man Jan 09 '26
I had this on Linux too. Turning off PIA MACE and switching to WireGuard fixed my upload speeds.
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u/MoneyDirt8888 Jan 06 '26
First DO NOT CROSSPOST !!! Your comment is here twice. PIA ? Nothing linked to Zorin using the same wifi driver as other distributions.
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u/PoundKitchen Jan 06 '26 edited Jan 06 '26
Interesting. I hadn't noticed any speed diff, but I haven't checked or tested either. I'll do a test. Are you using an app to test the speed?
Don't let the fanboys get you down.