show help message when perf is permission denied #64
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When perf events cannot be opened due to permission being denied, the user should be able to configure their system so that poop can be run without elevated permissions (e.g. without using sudo ). To assist with this poop will now display a message explaining how the `kernel.perf_event_paranoid` setting can be changed. The displayed is based on the one used by the `perf` tool. Some systems (notably Debian and Ubuntu) carry linux patches that add additional levels for perf_events_paranoid which means that the highest (i.e. least permissive) value that allows poop to access perf events is different on different systems. Due to this, the help message suggests lowering the perf_event_paranoid setting by one.
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Resolves #17.
See the commit message for details on the message displayed.
Some bikeshedding on the message may be warranted - it's probably reasonable to have a simpler strategy for suggesting the perf_event_paranoid setting suggested. I chose to suggest decrementing the perf_event_paranoid setting by one because:
A simpler strategy would be to just suggest level 2, which I think should work for everyone since poop doesn't ask for kernel events and surely distros with patches changing the levels will preserve the meaning of the mainline ones.