Introduction

fptrace is a Linux process tracing tool that records process launches and file accesses. Results can be saved in a deps.json file or used to generate launcher scripts. It works like strace but produces machine readable output and resolves relative pathnames into absolute ones. Optionally it also records environment variables and prevents deletions. It incurs much less overhead than strace thanks to seccomp filtering.

deps.json

fptrace -d deps.json sh -c 'echo a > a; cat a | tee b; exec test -d a' in /tmp makes:

[
  {
    "Cmd": {
      "Parent": 1, "ID": 2,
      "Dir": "/tmp", "Path": "/bin/cat", "Args": ["cat", "a"]
    },
    "Inputs": ["/etc/ld.so.cache", "/lib/x86_64-linux-gnu/libc.so.6", "/tmp/a"],
    "Outputs": ["/dev/fptrace/pipe/1"],
    "FDs": {"0": "/dev/stdin", "1": "/dev/fptrace/pipe/1", "2": "/dev/stderr"}
  },
  {
    "Cmd": {
      "Parent": 1, "ID": 3,
      "Dir": "/tmp", "Path": "/usr/bin/tee", "Args": ["tee", "b"]
    },
    "Inputs": ["/etc/ld.so.cache", "/lib/x86_64-linux-gnu/libc.so.6", "/dev/fptrace/pipe/1"],
    "Outputs": ["/tmp/b", "/dev/stdout"],
    "FDs": {"0": "/dev/fptrace/pipe/1", "1": "/dev/stdout", "2": "/dev/stderr"}
  },
  {
    "Cmd": {
      "Parent": 0, "ID": 1, "Exec": 4,
      "Dir": "/tmp", "Path": "/bin/sh", "Args": ["sh", "-c", "echo a > a; cat a | tee b; exec false"]
    },
    "Inputs": ["/etc/ld.so.cache", "/lib/x86_64-linux-gnu/libc.so.6"],
    "Outputs": ["/tmp/a"],
    "FDs": {"0": "/dev/stdin", "1": "/dev/stdout", "2": "/dev/stderr"}
  },
  {
    "Cmd": {
      "Parent": 1, "ID": 4, "Exit": 1,
      "Dir": "/tmp", "Path": "/bin/false", "Args": ["false"]
    },
    "Inputs": ["/etc/ld.so.cache", "/lib/x86_64-linux-gnu/libc.so.6"],
    "Outputs": [],
    "FDs": {"0": "/dev/stdin", "1": "/dev/stdout", "2": "/dev/stderr"}
  }
]

The result is a list of command executions (ordered by the time of their exit): an execution begins with an execve and ends with the last spawned thread or fork.

• ID is a unique execution identifier (counting from 1)
• Parent is the ID of the execution that spawned it
• Exit is the exit code of the first process of the execution (omitted if zero, negative on death by signal)
• Exec is the ID of next execution, if the first process has spawned it before the exit
• Dir is the initial working directory
• Path is an absolute path to the executable
• Args are execve arguments
• FDs are initial file descriptors

Inputs and Outputs list chronologically absolute paths to files opened for reading and writing, except that files opened for writing and later opened for reading are not listed as execution Inputs. /dev/fptrace/pipe/ is a fictional directory that enumerates pipes.

Launcher scripts

fptrace -s /tmp/scripts sh -c 'echo a > a; cat a | tee b' generates 0-1-sh, 1-2-cat, and 1-3-tee:

• 0-1-sh

#!/bin/sh
cd /tmp
${exec:-exec} sh -c 'echo a > a; cat a | tee b' "$@"

• 1-2-cat

#!/bin/sh
cd /tmp
${exec:-exec} cat a "$@"

• 1-3-tee

#!/bin/sh
cd /tmp
${exec:-exec} tee b "$@"

Installation

With go get:

go get github.com/orivej/fptrace
go generate github.com/orivej/fptrace

With Nix:

nix-env -if https://github.com/orivej/fptrace/archive/master.tar.gz