Darwin debugging for the Linux developer

These technical notes are meant to explain to a Linux developer what are the equivalents to debug certain things over Darwin.

Key differences from Linux

Linux tool	macOS equivalent	Purpose
`strace`	`dtruss` (1), `strace-macos`	System call tracing
`perf`	`sample`, `spindump`, `Instruments` (2)	Performance profiling
`ss`	`netstat -nv`	Socket statistics
`iostat`	`iostat -Id`	Disk I/O statistics
`lsof`	`lsof`	Open file listings
`/proc`	`vmmap`, `heap`, `lsof`	Process/memory information
`blktrace`	`fs_usage -wf filesys`	Trace real-time IO activity

(1): dtruss is unavailable on systems with System Integrity Protection enabled (SIP). Lix CI machines have SIP enabled. (2): Instruments is a graphical application that requires a remote desktop and cannot be used over SSH.

Getting flamegraphs out of `sample`

Combine https://github.com/brc7/flamegraph-sample/blob/master/stackcollapse-sample.py with https://speedscope.app/.

Inspecting memory allocations

heap can give a list of allocations sorted by sizes when it can recognize the type in-memory (doesn't always work for everything).

`iostat` tips

iostat -Id on macOS will return as the first row the cumulative data SINCE the first boot.

xfrs := IO operations per second.

Listing file descriptors

/proc doesn't exist on macOS, therefore, lsof is the only thing that can list file descriptors and let you understand the relationships.

Tracing network activity

fs_usage -wf network can trace real-time network activity on file descriptors.

Checking Internet quality

networkQuality -v will dump an Apple-infrastructure Internet connection check for bandwidth and latency.