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Under remote (ssh) GNU screen and tmux sessions large output causes horrible performance #10019

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opened 2026-01-31 02:10:18 +00:00 by claunia · 2 comments
claunia commented 2026-01-31 02:10:18 +00:00
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Originally created by @jblaine on GitHub (Aug 5, 2020).

Environment

Windows build number: Microsoft Windows [Version 10.0.18363.959]
Windows Terminal version (if applicable): 1.1.2021.0

Windows 10 native ssh client
Remote Linux host running either tmux or GNU screen, multiple versions all work to reproduce issue

Steps to reproduce

ssh to a host
run screen or tmux or attach to an existing session of either
run cat on a large text file, such as one with 3000+ lines

Expected behavior

Terminal should display a somewhat consistent stream of text, like PuTTY, Powershell on its own, CMD.EXE on its own, and other tools do.

Actual behavior

Terminal displays a little, pauses for several seconds, displays some more, pauses, etc

Originally created by @jblaine on GitHub (Aug 5, 2020). <!-- 🚨🚨🚨🚨🚨🚨🚨🚨🚨🚨 I ACKNOWLEDGE THE FOLLOWING BEFORE PROCEEDING: 1. If I delete this entire template and go my own path, the core team may close my issue without further explanation or engagement. 2. If I list multiple bugs/concerns in this one issue, the core team may close my issue without further explanation or engagement. 3. If I write an issue that has many duplicates, the core team may close my issue without further explanation or engagement (and without necessarily spending time to find the exact duplicate ID number). 4. If I leave the title incomplete when filing the issue, the core team may close my issue without further explanation or engagement. 5. If I file something completely blank in the body, the core team may close my issue without further explanation or engagement. All good? Then proceed! --> <!-- This bug tracker is monitored by Windows Terminal development team and other technical folks. **Important: When reporting BSODs or security issues, DO NOT attach memory dumps, logs, or traces to Github issues**. Instead, send dumps/traces to secure@microsoft.com, referencing this GitHub issue. If this is an application crash, please also provide a Feedback Hub submission link so we can find your diagnostic data on the backend. Use the category "Apps > Windows Terminal (Preview)" and choose "Share My Feedback" after submission to get the link. Please use this form and describe your issue, concisely but precisely, with as much detail as possible. --> # Environment ```none Windows build number: Microsoft Windows [Version 10.0.18363.959] Windows Terminal version (if applicable): 1.1.2021.0 Windows 10 native ssh client Remote Linux host running either tmux or GNU screen, multiple versions all work to reproduce issue ``` # Steps to reproduce ssh to a host run `screen` or `tmux` or attach to an existing session of either run `cat` on a large text file, such as one with 3000+ lines # Expected behavior Terminal should display a somewhat consistent stream of text, like PuTTY, Powershell on its own, CMD.EXE on its own, and other tools do. # Actual behavior Terminal displays a little, pauses for several seconds, displays some more, pauses, etc
claunia added the Needs-TriageNeeds-Tag-FixNeeds-AttentionArea-Performance labels 2026-01-31 02:10:18 +00:00
claunia commented 2026-01-31 02:10:19 +00:00
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@zadjii-msft commented on GitHub (Aug 5, 2020):

Correct me if I'm wrong, but how is this different from #7019? It might be best to merge this discussion with that thread.

  • Does this repro without tmux/screen running on the remote host?
  • Does this repro with the ssh from a WSL distro?
  • More insane - if you run wsl.exe ssh.exe <args to ssh...> inside a legacy powershell/cmd window, does the same issue repro? This will cause wsl to create a conpty to host ssh.exe, which could help identify if the issue is conpty vs something else.

I'm also thinking this might be related to conpty buffering the frames to at least 1/60th of a second, maybe something weird in this situation is causing that delay to seem much larger

@zadjii-msft commented on GitHub (Aug 5, 2020): Correct me if I'm wrong, but how is this different from #7019? It might be best to merge this discussion with that thread. * Does this repro **without** `tmux`/`screen` running on the remote host? * Does this repro with the `ssh` from a WSL distro? * More insane - if you run `wsl.exe ssh.exe <args to ssh...>` inside a legacy powershell/cmd window, does the same issue repro? This will cause wsl to create a conpty to host `ssh.exe`, which could help identify if the issue is conpty vs something else. I'm also thinking this might be related to conpty buffering the frames to at least 1/60th of a second, maybe something weird in this situation is causing that delay to seem much larger
claunia commented 2026-01-31 02:10:19 +00:00
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@jblaine commented on GitHub (Aug 5, 2020):

Sure, I'm fine merging my comments over there. The info in #7019 seemed a little different to me at the time I created this.

I'll close this in favor of #7019

@jblaine commented on GitHub (Aug 5, 2020): Sure, I'm fine merging my comments over there. The info in #7019 seemed a little different to me at the time I created this. I'll close this in favor of #7019
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Reference: starred/terminal#10019
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