scrollback-limit value not respected

[iplambert]

Issue Description

scrollback-limit is not being applied correctly. The effective scrollback is significantly less than the configured value, and counterintuitively, a higher configured limit results in less accessible scrollback than a lower one.

Additional context
The backwards scaling between configured value and effective scrollback (higher limit → less scrollback) suggests a possible integer overflow, unit mismatch, or buffer allocation error introduced in 1.3.x rather than a simple config parsing issue.

Expected Behavior

Steps to reproduce

Set scrollback-limit = 10000 in config, fully restart Ghostty
Run cmd+k to clear scrollback buffer
Run for i in $(seq 10000); do echo $i; done
Scroll to the top of the buffer

Expected: scrollback begins at or near line 1
Observed: scrollback begins at approximately line 9079 (~921 lines accessible)

Repeating with scrollback-limit = 500:

Scrollback begins at approximately line 9574 (~426 lines accessible)

The lower configured value produces more accessible scrollback, which is the inverse of expected behavior.

Actual Behavior

Observed: scrollback begins at approximately line 9079 (~921 lines accessible) and the lower configured value produces more accessible scrollback, which is the inverse of expected behavior.

Reproduction Steps

Steps to reproduce

Set scrollback-limit = 10000 in config, fully restart Ghostty
Run cmd+k to clear scrollback buffer
Run for i in $(seq 10000); do echo $i; done
Scroll to the top of the buffer

Ghostty Logs

Filtering the log data using "subsystem == "com.mitchellh.ghostty""
Timestamp                       Thread     Type        Activity             PID    TTL  
2026-04-21 13:59:31.448454+0200 0x44960e   Info        0x0                  80790  0    ghostty: [com.mitchellh.ghostty:default] ghostty version=1.3.1
2026-04-21 13:59:31.448906+0200 0x44960e   Info        0x0                  80790  0    ghostty: [com.mitchellh.ghostty:default] ghostty build optimize=ReleaseFast
2026-04-21 13:59:31.448918+0200 0x44960e   Info        0x0                  80790  0    ghostty: [com.mitchellh.ghostty:default] runtime=.none
2026-04-21 13:59:31.448924+0200 0x44960e   Info        0x0                  80790  0    ghostty: [com.mitchellh.ghostty:default] font_backend=.coretext
2026-04-21 13:59:31.448928+0200 0x44960e   Info        0x0                  80790  0    ghostty: [com.mitchellh.ghostty:default] renderer=renderer.generic.Renderer(renderer.Metal)
2026-04-21 13:59:31.448932+0200 0x44960e   Info        0x0                  80790  0    ghostty: [com.mitchellh.ghostty:default] libxev default backend=kqueue
2026-04-21 13:59:31.449096+0200 0x44960e   Info        0x0                  80790  0    ghostty: [com.mitchellh.ghostty:os_locale] os_locale: setlocale from env result=en_US.UTF-8
2026-04-21 13:59:31.449249+0200 0x44960e   Info        0x0                  80790  0    ghostty: [com.mitchellh.ghostty:default] executing CLI action=.version

Ghostty Version

ghostty +version
Ghostty 1.3.1

Version
  - version: 1.3.1
  - channel: stable
Build Config
  - Zig version   : 0.15.2
  - build mode    : .ReleaseFast
  - app runtime   : .none
  - font engine   : .coretext
  - renderer      : renderer.generic.Renderer(renderer.Metal)
  - libxev        : kqueue

OS Version Information

Darwin Ivans-MacBook-Pro.local 25.4.0 Darwin Kernel Version 25.4.0: Thu Mar 19 19:33:25 PDT 2026; root:xnu-12377.101.15~1/RELEASE_ARM64_T6041 arm64 arm Darwin

(Linux only) Display Server

None

(Linux only) Desktop Environment/Window Manager

No response

Minimal Ghostty Configuration

all default. You se the built in settings button to open the config file and add:

scrollback-limit = 10000

Additional Relevant Configuration

on Apple Terminal and iTerm2 it works normally.

I acknowledge that:

• I have reviewed the FAQ and confirm that my issue is NOT among them.
• I have searched the Ghostty repository (both open and closed Discussions and Issues) and confirm this is not a duplicate of an existing issue or discussion.
• I have checked the "Preview" tab on all text fields to ensure that everything looks right, and have wrapped all configuration and code in code blocks with a group of three backticks (```) on separate lines.

[danielwe]

scrollback-limit works as follows:

• It's bytes, not lines.
• It applies to the page buffer holding the processed terminal content, including decoded codepoints and per-cell and per-line style and color information. This takes an order of magnitude more space than the "equivalent" utf8-encoded text file (very roughly 12.5 bytes per cell as far as I recall, but this amortizes per-line data, so the exact number depends on the width of your terminal in addition to the amount of coloring and styling).
• Blank cells are also represented, so the width of the terminal matters a lot, and even if the content is a narrow column (like seq 10000) you don't get more lines than if your content uses the full width.
• Finally: for implementation reasons, the scrollback is always at least two memory pages, which is much more than 10000 bytes. So both 10000 and 500 are rounded up to the minimum. The discrepancy you observed is likely because the width of your terminal window was different in the two experiments.¹

This has been discussed several times before, so search the discussions for more details.

Footnotes

1. Your numbers indicate that you got less scrollback with 500 than 10000, while your description claims it was more. Either way, the true limit in bytes was the same in both cases, and the difference was probably due to the width of the terminal window. ↩