Accessing some CPU performance counters may require root permissions or a reduced paranoia level in /proc/sys/kernel/perf_event_paranoid. On hardened kernels any access by unprivileged users is forbidden by default. The paranoia level can be set by root with e.g. # echo 2 > /proc/sys/kernel/perf_event_paranoid perf event paranoia level (from kernel/events/core.c in src:linux): -1 - not paranoid at all 0 - disallow raw tracepoint access for unpriv 1 - disallow cpu events for unpriv (Linux default) 2 - disallow kernel profiling for unpriv 3 - disallow all unpriv perf event use (Debian default)