Skip recursive home chown when ownership is correct#62
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With user-namespace-backed virtiofs (the default on Linux since the CAP_SETGID fix), the rootfs already has correct uid/gid ownership via xattr.SetOverrideStat. The previous code walked the entire home directory tree (~120K files, ~5GB for claude-code images) doing Lchown on every entry, adding ~14 seconds to guest boot. Now check whether the home dir is already owned by the sandbox user and, if so, only walk the .ssh/ subtree to enforce strict SSH permissions. The full recursive chown is preserved as a fallback for platforms without user namespaces (e.g. macOS). Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Summary
chownof/home/sandboxwhen the directory is already owned by the correct uid/gid (the common case on Linux with user-namespace-backed virtiofs).ssh/to enforce strict SSH permissions (0700 dirs, 0600 files)Problem
fixHomeOwnershipwas doing afilepath.WalkDir+Lchownon every file under/home/sandbox. For the claude-code guest image this is ~120K files / ~5GB, taking ~14 seconds of guest boot time. This was the single largest contributor to slow VM startup.Since we now use user namespaces (
WithUserNamespaceUID), libkrun's virtiofs passthrough hasCAP_SETGIDwithin the namespace, andxattr.SetOverrideStaton the rootfs already gives the guest correct ownership. The recursive chown was redundant on Linux.Result
Measured with OTel tracing (
--trace) on the brood-box CLI:microvm.SSHWaitReadyTest plan
go test ./...— all tests passbrood-boxend-to-end:bbox claude-code --trace --timingsshows 7.4s Sandbox ready🤖 Generated with Claude Code