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GeezerVison is showing github.com — ublk devices unopenable in 2.2.x: char major 249 (ublk-char) and block major 259 (/dev/ublkb*) are missing from the device allowlist · Issue #2798 · orbstack/orbstack

ublk devices unopenable in 2.2.x: char major 249 (ublk-char) and block major 259 (/dev/ublkb*) are missing from the device allowlist #2798

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ublk devices unopenable in 2.2.x: char major 249 (ublk-char) and block major 259 (/dev/ublkb*) are missing from the device allowlist#2798
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Description

@graveland
graveland
opened on Nov 12, 2026
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Describe the bug

ublk_drv is present in Linux machines (added in 1.7.5, #1498), and /dev/ublk-control works. But on 2.2.5 it can't create a usable device: open("/dev/ublkc0") returns EPERM as root with full capabilities. It looks like the same cgroup v2 device allowlist regression as #2524, #2528 and #2635, for different majors.

Request

Allow these in the machine device allowlist:

  • char major of ublk-char (249 here, but dynamic, so it would be better resolved by name from /proc/devices at module load than hardcoded)
  • block major 259 (BLOCK_EXT_MAJOR), which /dev/ublkb* uses
  • /dev/ublk-control is already fine

Also worth fixing if you could please: machines have no devtmpfs-backed /dev, so /dev/ublkc* and /dev/ublkb* aren't created automatically. A ublk server needs both nodes to appear, whether through devtmpfs or by bind-mounting nodes as OrbStack does for /dev/ublk-control.

To Reproduce

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Expected behavior

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Diagnostic report (REQUIRED)

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Activity

  1. graveland
    added
    t/bugSomething isn't workingSomething isn't working
    on Nov 12, 2026

  2. orbstack-bot commented on Nov 12, 2026

    @orbstack-bot
    orbstack-botBot
    on Nov 12, 2026
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    Hi! Please upload a diagnostic report from the OrbStack menu > Help > Upload Diagnostics (or run orb report) and then paste the output here. The extra info makes it easier for us to debug issues.

    It should look like:

    System info:
[...]

Full report: orbstack.dev/[...].zip

    (It's safe to post the link publicly — only the OrbStack team can access it.)

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