🤖 fix: cpu.max file not found error in init.scope cgroup #27
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On systems running RKE2 with sysbox where /proc/self/cgroup reports 0::/init.scope, the code was failing because /sys/fs/cgroup/init.scope/cpu.max doesn't exist. The error occurred because cpuUsed() and cpuTotal() tried to read the CPU period directly from the missing file without falling back to parent cgroups. Changes: - Added cpuPeriod() helper method that follows the same pattern as cpuQuota() - The new method handles fs.ErrNotExist and strconv.ErrSyntax errors - Falls back to parent cgroup when cpu.max is missing (common in system-level cgroups like init.scope) - Updated cpuUsed() to use cpuPeriod() instead of directly reading - Updated cpuTotal() to use cpuPeriod() instead of directly reading - Added test case fsContainerCgroupV2InitScope to verify the fix The fix ensures consistent parent fallback behavior across all values read from cpu.max (quota, period, and usage calculations). Fixes issue where systems report: /sys/fs/cgroup/init.scope/cpu.max file does not exist
Per Linux kernel documentation, cpu.max has a default value of "max 100000" where 100000 microseconds (100ms) is the default period. The file exists on non-root cgroups, but in practice may be missing in certain scenarios. When cpu.max cannot be found anywhere in the cgroup hierarchy, instead of returning an error, we now use the documented default period of 100000 microseconds. This makes the code more robust and aligns with kernel behavior. Changes: - Added cgroupV2DefaultPeriodUs constant (100000) - Updated cpuPeriod() to return default period instead of error when no parent exists - Added test fixture fsContainerCgroupV2InitScopeNoCPUMax - Added test case CPU/InitScopeDefaultPeriod to verify default period behavior Ref: https://docs.kernel.org/admin-guide/cgroup-v2.html#cpu-interface-files
johnstcn
approved these changes
Nov 7, 2025
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On systems running RKE2 with sysbox where /proc/self/cgroup reports 0::/init.scope, the code was failing because /sys/fs/cgroup/init.scope/cpu.max doesn't exist. The error occurred because cpuUsed() and cpuTotal() tried to read the CPU period directly from the missing file without falling back to parent cgroups.
Changes:
The fix ensures consistent parent fallback behavior across all values read from cpu.max (quota, period, and usage calculations).
Fixes issue where systems report: /sys/fs/cgroup/init.scope/cpu.max file does not exist
🤖 PR was written by Claude Sonnet 4.5 Thinking using Coder Mux and reviewed by a human 👩