obs

Linux Observability Primitives

Very grand title for a humble start. This repository contains my experiments with low level Linux observability, in Go.

If you are interested in the domain, you should probably check out bcc and gobpf. They support eBPF. I may integrate eBPF support at some point, either through gobpf of directly, but that's a whole different story.

Tracepoints

Tracepoints are static probes placed at critical points in the Linux kernel. There are some tracepoints for many interesting events:

• Scheduler: when does a process starts & exits, context switches.
• I/O: follow block requests.
• Filesystem: intimate details about filesystem operations (ext4, btrfs, ... are instrumented).
• KVM: watch what KVM does, eg. VM exits.
• Drivers: eg. on can follow Intel GPU execution requests and display events (i915 driver).
• Syscall entry/exit.
• Many other events and Various drivers.

To see the full list of tracepoints:

$ sudo perf list tracepoint
[...]
  sched:sched_kthread_stop                           [Tracepoint event]
  sched:sched_kthread_stop_ret                       [Tracepoint event]
  sched:sched_migrate_task                           [Tracepoint event]
  sched:sched_move_numa                              [Tracepoint event]
  sched:sched_process_exec                           [Tracepoint event]
  sched:sched_process_exit                           [Tracepoint event]
  sched:sched_process_fork                           [Tracepoint event]
  sched:sched_process_free                           [Tracepoint event]
  sched:sched_process_hang                           [Tracepoint event]
  sched:sched_process_wait                           [Tracepoint event]
[...]

Example

// Listen for the sched_process_exec, triggered when a process does an exec(),
// and display the process pid and the path of binary being exec'ed. Error
// handling is omitted.
observer := obs.NewObserver()
observer.AddTracepoint("sched:sched_process_exec")
observer.Open()

for {
  event, _ := observer.ReadEvent()
  tp := event.(*obs.TracepointEvent)
  fmt.Printf("exec\t%d\t%s\n", tp.GetInt("pid"), tp.GetString("filename"))
}

The output below is the result of running docker run busybox sleep 3600 and shows the (surprisingly big) list programs that end up being executed up to runc and the sleep process in the container.

exec	7364	/usr/bin/docker
exec	7370	/sbin/auplink
exec	7371	/sbin/auplink
exec	7378	/lib/udev/ifupdown-hotplug
exec	7380	/bin/grep
exec	7381	/sbin/ifquery
exec	7379	/sbin/ifquery
exec	7382	/lib/udev/ifupdown-hotplug
exec	7383	/lib/systemd/systemd-sysctl
exec	7385	/bin/grep
exec	7386	/sbin/ifquery
exec	7384	/sbin/ifquery
exec	7387	/lib/systemd/systemd-sysctl
exec	7389	/usr/bin/docker-containerd-shim
exec	7397	/usr/bin/docker-runc
exec	7404	/proc/self/exe
exec	7413	/usr/bin/dockerd
exec	7426	/proc/self/exe
exec	7433	/lib/udev/ifupdown-hotplug
exec	7434	/usr/bin/docker-runc
exec	7407	/bin/sleep