otinstaller · Domain and DNS

Install Fierce on Linux in one command

Fierce brute-forces subdomains with a wordlist, tries zone transfers, and scans the IP space around the hosts it finds for more names. It is an old-school DNS recon tool that still works.

Fierce in three lines

pipx install otinstaller
ot install fierce
ot run fierce -- d:example.com

Runs mschwager/fierce (GPL-3.0, ★ 1.8k, otinstaller v0.0.4, registry updated Oct 13, 2026). otinstaller installs and runs it; it does not change or verify it.

What Fierce is for

Finding non-contiguous IP ranges tied to a domain.
Zone transfer checks on your own name servers.

Typed inputs for Fierce

otinstaller translates these prefixes into Fierce's own flags. Anything else after -- is passed through unchanged, so every original flag still works.

d:: domain · ot run fierce -- d:example.com

It also takes ip input through its own flags; there is no typed prefix for those yet.

Run every installed tool that takes the same input at once: ot run --all d:example.com

Where the results go

Every run lands under ./results/fierce/<target>/ as a timestamped output file plus a .meta.json sidecar: the exact command, start and end time, exit code, and the SHA-256 of the output. Group runs with --case, compare the last two with ot diff fierce <target>, and pull indicators out with ot extract.

Before you run it

Brute force and zone transfer attempts are visible to the target's DNS operators.

Update, remove, inspect

ot info fierce      # inputs, flags, keys
ot example fierce   # sample output
ot update fierce    # move to the next tested version
ot remove fierce    # delete its virtualenv

Full reference for this tool: docs for fierce.

Pairs with

ctfr

ctfr lists the subdomains of a domain by reading Certificate Transparency logs through crt.sh.

dnsgen

dnsgen takes a list of known subdomains and generates plausible permutations: numbers, environments, regions, and common words.

BBOT

BBOT is a recursive scanner that starts from a domain or IP, discovers subdomains, hosts, and services, and feeds each finding back in as a new target.

FAQ

Fierce with otinstaller, answered

How do I install Fierce on Kali or Ubuntu?

Install otinstaller once with pipx install otinstaller, run ot init, then ot install fierce. The tool lands in its own virtualenv under ~/.otinstaller/, pinned to a version that was tested on Ubuntu, so nothing touches your system Python. ot doctor flags a missing git or venv module.

Which inputs does Fierce take through otinstaller?

d: (domain). otinstaller maps each prefix to Fierce's own flag. Everything after -- that is not a typed input is passed through unchanged, so the original flags still work.

Where does otinstaller save Fierce results?

Under ./results/fierce/<target>/ in the folder you run from, as a timestamped output file plus a .meta.json sidecar with the exact command, timing, exit code, and SHA-256. Add --case <name> to group runs, and ot diff fierce <target> to compare the last two.

Does Fierce need an API key or a login?

No key is required for the basic run. Optional keys, where the project supports them, go in ~/.otinstaller/.env and are passed only to tools that declare them.

Can I run Fierce together with other tools?

Yes. ot run --all d:example.com runs every installed tool that accepts domain input, in parallel, including Fierce. Save the combination as a playbook to repeat it.