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docs/CONTROL_GROUP_INTERFACE.md: document accounting information available via D-Bus

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Jeffrey Bosboom 2024-07-24 18:14:24 -07:00 committed by Luca Boccassi
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@ -223,7 +223,7 @@ Use these APIs to register any kind of process workload with systemd to be place
### Reading Accounting Information
Note that there's currently no systemd API to retrieve accounting information from cgroups. For now, if you need to retrieve this information use `/proc/$PID/cgroup` to determine the cgroup path for your process in the `cpuacct` controller (or whichever controller matters to you), and then read the attributes directly from the cgroup tree.
Accounting information is available via the `MemoryCurrent`, `MemoryPeak`, `MemorySwapCurrent`, `MemorySwapPeak`, `MemoryZSwapCurrent`, `MemoryAvailable`, `EffectiveMemoryMax`, `EffectiveMemoryHigh`, `CPUUsageNSec`, `EffectiveCPUs`, `EffectiveMemoryNodes`, `TasksCurrent`, `EffectiveTasksMax`, `IPIngressBytes`, `IPIngressPackets`, `IPEgressBytes`, `IPEgressPackets`, `IOReadBytes`, `IOReadOperations`, `IOWriteBytes`, and `IOWriteOperations` D-Bus properties. To read this and other information directly from the cgroup tree, get the unit's cgroup path (relative to `/sys/fs/cgroup`) from the `ControlGroup` property, by calling [`sd_pid_get_cgroup()`](https://www.freedesktop.org/software/systemd/man/latest/sd_pid_get_cgroup.html), or by parsing `/proc/$PID/cgroup`.
If you want to collect the exit status and other runtime parameters of your transient scope or service unit after the processes in them ended set the `RemainAfterExit` boolean property when creating it. This will has the effect that the unit will stay around even after all processes in it died, in the `SubState="exited"` state. Simply watch for state changes until this state is reached, then read the status details from the various properties you need, and finally terminate the unit via `StopUnit()` on the `Manager` object or `Stop()` on the `Unit` object itself.