Threads and Connection Limits

A High-Level Overview

This section explains how the -t and -L options work together to determine the overall aggressiveness of a scan. The combination of the two values set by these options determines how hard your target will get hit and to some extent also determines how many resources will be consumed on your local machine.

A Note on Green Threads

feroxbuster uses so-called green threads as opposed to traditional kernel/OS threads. This means (at a high-level) that the threads are implemented entirely in userspace, within a single running process. As a result, a scan with 30 green threads will appear to the OS to be a single process with no additional light-weight processes associated with it as far as the kernel is concerned. As such, there will not be any impact to process (nproc) limits when specifying larger values for -t. However, these threads will still consume file descriptors, so you will need to ensure that you have a suitable nlimit set when scaling up the amount of threads. More detailed documentation on setting appropriate nlimit values can be found in the No File Descriptors Available section of the FAQ

The Implementation

• Threads: The -t option specifies the maximum amount of active threads per-directory during a scan
• Connection Limits: The -L option specifies the maximum amount of active connections per thread

Examples

To truly have only 30 active requests to a site at any given time, -t 30 -L 1 is necessary. Using -t 30 -L 2 will result in a maximum of 60 total requests being processed at any given time for that site. And so on. For a conversation on this, please see Issue #126 which may provide more (or less) clarity 😉