---
title: Spying on running Ruby processes
published: "2015-11-17"
publisher: Honeybadger
author: Starr Horne
category: Ruby articles
tags:
  - Ruby
description: "Did you know that it's possible to log all method calls as they occur in a running process in real time? How about injecting code to be executed inside of a running process? You can – via the magic of the rbtrace gem."
url: "https://www.honeybadger.io/blog/spying-on-running-ruby-processes/"
---

Did you know that it's possible to log all method calls as they occur in a running process in real time? How about injecting code to be executed inside of a running process? You can – via the magic of the `rbtrace` gem.

The `rbtrace` gem comes with two parts. The first is a library that you include in the code that you want to trace. The second is a commandline utility for querying trace data.

Let's take a look at a simple example. The code that we're going to trace is really simple. All we have to do is require the `rbtrace` gem.

```ruby
require 'rbtrace' require 'digest' require 'securerandom' # An infinite loop while true # Do some work. Digest::SHA256.digest SecureRandom.random_bytes(2**8) # Sleep for one second on every iteration. sleep 1 end
```

Now let's run this program:

```
$ ruby trace.rb & [1] 12345
```

We take this process ID and give it to the `rbtrace` command line tool. The `-f` option indicates "firehose" mode, which prints everything to screen.

```ruby
$ rbtrace -p 12345 -f *** attached to process 12345 Fixnum#** <0.000010> SecureRandom.random_bytes Integer#to_int <0.000005> SecureRandom.gen_random OpenSSL::Random.random_bytes <0.002223> SecureRandom.gen_random <0.002243> SecureRandom.random_bytes <0.002290> Digest::SHA256.digest Digest::Class#initialize <0.000004> Digest::Instance#digest Digest::Base#reset <0.000005> Digest::Base#update <0.000210> Digest::Base#finish <0.000006> Digest::Base#reset <0.000005> Digest::Instance#digest <0.000267> Digest::SHA256.digest <0.000308> Kernel#rand Kernel#respond_to_missing? <0.000008> Kernel#rand <0.000071> Kernel#sleep <1.003233>
```

This is really cool! We can see every method that gets called along with the time spent in that method.

If we wanted to home in on a specific method, we could use the `-m` option.

```ruby
$ rbtrace -p 12345 -m digest *** attached to process 12345 Digest::SHA256.digest Digest::Instance#digest <0.000201> Digest::SHA256.digest <0.000220> Digest::SHA256.digest Digest::Instance#digest <0.000287> Digest::SHA256.digest <0.000343>
```

Probably the coolest use of this gem is to get a heap dump from a running web server. Heap dumps contain every object in memory along with a bunch of metadata and are very useful for debugging memory leaks in production.

To get the heap dump use a command like the one below, taken from [this post](http://samsaffron.com/archive/2015/03/31/debugging-memory-leaks-in-ruby) by Sam Saffron.

```
$ bundle exec rbtrace -p <SERVER PID HERE> -e 'Thread.new{GC.start;require "objspace";io=File.open("/tmp/ruby-heap.dump", "w"); ObjectSpace.dump_all(output: io); io.close}'
```

Be warned though, heap dumps can be very big – on the order of a few hundred megabytes for a rails process. Here's a very small sample:

```json
[ { "type": "ROOT", "root": "vm", "references": [ "0x7fb7d38bc3f0", "0x7fb7d38b79b8", "0x7fb7d38dff80", "0x7fb7d38bff50", "0x7fb7d38bff00", "0x7fb7d38b4bf0", "0x7fb7d38bfe88", "0x7fb7d38bfe60", "0x7fb7d38ddc80", "0x7fb7d38dffa8", "0x7fb7d382fbd0", "0x7fb7d382fbf8" ] }, { "type": "ROOT", "root": "machine_context", "references": [ "0x7fb7d382fbf8", "0x7fb7d382fbf8", "0x7fb7d3827d40", "0x7fb7d3827a70", "0x7fb7d38becb8", "0x7fb7d38bed08", "0x7fb7d38ddc80", "0x7fb7d3827e58", "0x7fb7d3827e58", "0x7fb7d38becb8", "0x7fb7d38becb8", "0x7fb7d38bc328", "0x7fb7d38bc378", "0x7fb7d38ddc80", "0x7fb7d3835008", "0x7fb7d3835008", "0x7fb7d3835008", "0x7fb7d3835008", "0x7fb7d3835008" ] }, { "type": "ROOT", "root": "global_list", "references": [ "0x7fb7d38dff58" ] }, { "type": "ROOT", "root": "global_tbl", "references": [ "0x7fb7d38c6dc8", "0x7fb7d38c6dc8", "0x7fb7d38c65f8", "0x7fb7d38c6580", "0x7fb7d38c6508", "0x7fb7d38c6580", "0x7fb7d38c6288", "0x7fb7d38c6288", "0x7fb7d38c6288", "0x7fb7d38c6288", "0x7fb7d38c6288", "0x7fb7d38bc418", "0x7fb7d38bc418", "0x7fb7d38bc418", "0x7fb7d3835328", "0x7fb7d3835328" ] }, { "address": "0x7fb7d300c5e8", "type": "STRING", "class": "0x7fb7d38dcee8", "frozen": true, "embedded": true, "fstring": true, "bytesize": 10, "value": "@exit_code", "encoding": "US-ASCII", "memsize": 40, "flags": { "wb_protected": true, "old": true, "long_lived": true, "marked": true } }, { "address": "0x7fb7d300c7a0", "type": "STRING", "class": "0x7fb7d38dcee8", "frozen": true, "embedded": true, "fstring": true, "bytesize": 9, "value": "exit_code", "encoding": "US-ASCII", "memsize": 40, "flags": { "wb_protected": true, "old": true, "long_lived": true, "marked": true } }, { "address": "0x7fb7d300c908", "type": "STRING", "class": "0x7fb7d38dcee8", "frozen": true, "embedded": true, "fstring": true, "bytesize": 19, "value": "SystemExitException", "encoding": "US-ASCII", "memsize": 40, "flags": { "wb_protected": true, "old": true, "long_lived": true, "marked": true } }, { "address": "0x7fb7d300cb60", "type": "STRING", "class": "0x7fb7d38dcee8", "frozen": true, "embedded": true, "fstring": true, "bytesize": 17, "value": "VerificationError", "encoding": "US-ASCII", "memsize": 40, "flags": { "wb_protected": true, "old": true, "long_lived": true, "marked": true } }, { "address": "0x7fb7d300cd90", "type": "STRING", "class": "0x7fb7d38dcee8", "frozen": true, "embedded": true, "fstring": true, "bytesize": 19, "value": "RubyVersionMismatch", "encoding": "US-ASCII", "memsize": 40, "flags": { "wb_protected": true, "old": true, "long_lived": true, "marked": true } }, { "address": "0x7fb7d300cfe8", "type": "STRING", "class": "0x7fb7d38dcee8", "frozen": true, "embedded": true, "fstring": true, "bytesize": 21, "value": "RemoteSourceException", "encoding": "US-ASCII", "memsize": 40, "flags": { "wb_protected": true, "old": true, "long_lived": true, "marked": true } }, { "address": "0x7fb7d300d1f0", "type": "STRING", "class": "0x7fb7d38dcee8", "frozen": true, "fstring": true, "bytesize": 25, "value": "RemoteInstallationSkipped", "encoding": "US-ASCII", "memsize": 66, "flags": { "wb_protected": true, "old": true, "long_lived": true, "marked": true } }, { "address": "0x7fb7d300d3a8", "type": "STRING", "class": "0x7fb7d38dcee8", "frozen": true, "fstring": true, "bytesize": 27, "value": "RemoteInstallationCancelled", "encoding": "US-ASCII", "memsize": 68, "flags": { "wb_protected": true, "old": true, "long_lived": true, "marked": true } }, { "address": "0x7fb7d300d560", "type": "STRING", "class": "0x7fb7d38dcee8", "frozen": true, "embedded": true, "fstring": true, "bytesize": 11, "value": "RemoteError", "encoding": "US-ASCII", "memsize": 40, "flags": { "wb_protected": true, "old": true, "long_lived": true, "marked": true } }, { "address": "0x7fb7d300d830", "type": "STRING", "class": "0x7fb7d38dcee8", "frozen": true, "fstring": true, "bytesize": 26, "value": "OperationNotSupportedError", "encoding": "US-ASCII", "memsize": 67, "flags": { "wb_protected": true, "old": true, "long_lived": true, "marked": true } }, { "address": "0x7fb7d300dbc8", "type": "STRING", "class": "0x7fb7d38dcee8", "frozen": true, "embedded": true, "fstring": true, "bytesize": 12, "value": "InstallError", "encoding": "US-ASCII", "memsize": 40, "flags": { "wb_protected": true, "old": true, "long_lived": true, "marked": true } }, { "address": "0x7fb7d300e898", "type": "STRING", "class": "0x7fb7d38dcee8", "frozen": true, "embedded": true, "fstring": true, "bytesize": 9, "value": "requester", "encoding": "US-ASCII", "memsize": 40, "flags": { "wb_protected": true, "old": true, "long_lived": true, "marked": true } }, { "address": "0x7fb7d300eaa0", "type": "STRING", "class": "0x7fb7d38dcee8", "frozen": true, "embedded": true, "fstring": true, "bytesize": 13, "value": "build_message", "encoding": "US-ASCII", "memsize": 40, "flags": { "wb_protected": true, "old": true, "long_lived": true, "marked": true } }, { "address": "0x7fb7d300ec30", "type": "STRING", "class": "0x7fb7d38dcee8", "frozen": true, "embedded": true, "fstring": true, "bytesize": 8, "value": "@request", "encoding": "US-ASCII", "memsize": 40, "flags": { "wb_protected": true, "old": true, "long_lived": true, "marked": true } }, { "address": "0x7fb7d300ede8", "type": "STRING", "class": "0x7fb7d38dcee8", "frozen": true, "embedded": true, "fstring": true, "bytesize": 7, "value": "request", "encoding": "US-ASCII", "memsize": 40, "flags": { "wb_protected": true, "old": true, "long_lived": true, "marked": true } }, { "address": "0x7fb7d300efa0", "type": "STRING", "class": "0x7fb7d38dcee8", "frozen": true, "fstring": true, "bytesize": 27, "value": "ImpossibleDependenciesError", "encoding": "US-ASCII", "memsize": 68, "flags": { "wb_protected": true, "old": true, "long_lived": true, "marked": true } } ]
```

---

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