lock acmetool, an automatic certificate acquisition tool for ACME (Let's Encrypt)
By hlandau

certificate ssl letsencrypt acme tls acme-server acmetool x509

acmetool is an easy-to-use command line tool for automatically acquiring
certificates from ACME servers (such as Let's Encrypt). Designed to flexibly
integrate into your webserver setup to enable automatic verification. Unlike
the official Let's Encrypt client, this doesn't modify your web server

:white_check_mark: Zero-downtime autorenewal
:white_check_mark: Supports any webserver
:white_check_mark: Fully automatable
:white_check_mark: Single-file dependency-free binary
:white_check_mark: Idempotent
:white_check_mark: Fast setup

You can perform verifications using port 80 or 443 (if you don't yet have a
server running on one of them); via webroot; by configuring your webserver to
proxy requests for /.well-known/acme-challenge/ to a special port (402) which
acmetool can listen on; or by configuring your webserver not to listen on port
80, and instead running acmetool's built in HTTPS redirector (and challenge
responder) on port 80. This is useful if all you want to do with port 80 is
redirect people to port 443.

You can run acmetool on a cron job to renew certificates automatically (acmetool --batch). The
preferred certificate for a given hostname is always at
/var/lib/acme/live/HOSTNAME/{cert,chain,fullchain,privkey}. You can configure
acmetool to reload your webserver automatically when it renews a certificate.

acmetool is intended to be "magic-free". All of acmetool's state is stored in a
simple, comprehensible directory of flat files. The schema for this directory
is documented.

acmetool is intended to work like "make". The state directory expresses target
domain names, and whenever acmetool is invoked, it ensures that valid
certificates are available to meet those names. Certificates which will expire
soon are renewed. acmetool is thus idempotent and minimises the use of state.

acmetool can optionally be used without running it as
root. If you have
existing certificates issued using the official client, acmetool can import
those certificates, keys and account keys (acmetool import-le).

acmetool supports both RSA and ECDSA keys and certificates. acmetool's
notification hooks system allows you to write arbitrary shell scripts to be
executed when new certificates are obtained. By default, this is used to reload
webservers automatically, but it can also be used to distribute certificates to
other servers or for other purposes.

Getting Started

Binary releases: Binary releases are available.

Download the release appropriate for your platform and simply copy the
acmetool binary to /usr/bin.

_cgo releases are preferred over non-_cgo releases where available, but
non-_cgo releases may be more compatible with older OSes.

Ubuntu users: A binary release PPA, ppa:hlandau/rhea (package acmetool) is available.
$ sudo add-apt-repository ppa:hlandau/rhea
$ sudo apt-get update
$ sudo apt-get install acmetool

You can also download .deb files manually.

(Note: There is no difference between the .deb files for different Ubuntu release codenames; they are interchangeable and completely equivalent.)

Debian users: The Ubuntu binary release PPA also works with Debian:

echo 'deb http://ppa.launchpad.net/hlandau/rhea/ubuntu xenial main' > /etc/apt/sources.list.d/rhea.list
apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 9862409EF124EC763B84972FF5AC9651EDB58DFA
apt-get update
apt-get install acmetool


You can also download .deb files manually.

(Note: There is no difference between the .deb files for different Ubuntu release codenames; they are interchangeable and completely equivalent.)

RPM-based distros: A copr RPM repository is available.

If you have dnf installed:
$ sudo dnf copr enable hlandau/acmetool
$ sudo dnf install acmetool

Otherwise use the .repo files on the repository
page and use yum,
or download RPMs and use rpm directly.

Void Linux users: acmetool is in the repositories:

$ sudo xbps-install acmetool

Arch Linux users: An AUR PKGBUILD for building from source is available.

$ wget https://aur.archlinux.org/cgit/aur.git/snapshot/acmetool-git.tar.gz
$ tar xvf acmetool-git.tar.gz
$ cd acmetool-git
$ makepkg -s
$ sudo pacman -U ./acmetool*.pkg.tar.xz

Alpine Linux users: An APKBUILD for building from source is available.

FreeBSD users: FreeBSD port is available.

Building from source: You will need Go installed to build from source.

If you are on Linux, you will need to make sure the development files for
libcap are installed. This is probably a package for your distro called
libcap-dev or libcap-devel or similar.


This is necessary to work around a change in Git's default configuration
which hasn't yet been accounted for in some places.

$ git config --global http.followRedirects true

$ git clone https://github.com/hlandau/acme
$ cd acme
$ make && sudo make install

# (People familiar with Go with a GOPATH setup can alternatively use go get/go install:)
$ git config --global http.followRedirects true
$ go get github.com/hlandau/acme/cmd/acmetool

After installation


Run the quickstart wizard. Sets up account, cronjob, etc.
(If you want to use ECDSA keys or set RSA key size, pass "--expert".)

$ sudo acmetool quickstart

Configure your webserver to serve challenges if necessary.
See https://hlandau.github.io/acmetool/userguide#web-server-configuration

$ ...

Request the hostnames you want:

$ sudo acmetool want example.com www.example.com

Now you have certificates:

$ ls -l /var/lib/acme/live/example.com/

The quickstart subcommand is a recommended wizard which guides you through
the setup of ACME on your system.

The want subcommand states that you want a certificate for the given hostnames.
(If you want separate certificates for each of the hostnames, run the want
subcommand separately for each hostname.)

The default subcommand, reconcile, is like "make" and makes sure all desired
hostnames are satisfied by valid certificates which aren't soon to expire.
want calls reconcile automatically.

If you run acmetool reconcile on a cronjob to facilitate automatic renewal,
pass --batch to ensure it doesn't attempt to interact with a terminal.

You can increase logging severity for debugging purposes by passing

Validation Options

Webroot: acmetool can place challenge files in a given directory, allowing your normal
web server to serve them. The files must be served from the path you specify at

Information on configuring your web server.

Proxy: acmetool can respond to validation challenges by serving them on port 402. In
order for this to be useful, you must configure your webserver to proxy
requests under /.well-known/acme-challenge/ to

Information on configuring your web server.

Stateless: You configure your webserver to respond statelessly to
challenges for a given account key without consulting acmetool. This requires
nothing more than a one-time web server configuration change and no "moving
parts". Information on
configuring stateless

Redirector: acmetool redirector starts an HTTP server on port 80 which redirects all
requests to HTTPS, as well as serving any necessary validation responses. The
acmetool quickstart wizard can set it up for you if you use systemd.
Otherwise, you'll need to configure your system to run acmetool redirector
--service.uid=USERNAME --service.daemon=1
as a service, where USERNAME is
the username you want the daemon to drop to.

Make sure your web server is not listening on port 80.

Listen: If you are for some reason not running anything on port 80 or 443, acmetool
will use those ports. Either port being available is sufficient. This is only
really useful for development purposes.

Hook: You can write custom shell scripts (or binary executables) which
acmetool invokes to provision challenge files at the desired location. For
example, you could rsync challenge files to a directory on a remote server. More information.


acmetool will try to renew certificates automatically once they are 30 days
from expiry, or 66% through their validity period, whichever is lower.
Note that Let's Encrypt currently issues 90 day certificates.

acmetool will exit with an error message with nonzero exit status if it cannot
renew a certificate, so it is suitable for use in a cronjob. Ensure your system
is configured so that you get notifications of failing cronjobs.

If a cronjob fails, you should intervene manually to see what went wrong by
running acmetool (possibly with --xlog.severity=debug for verbose logging).


The client library which these utilities use can be used independently by any Go code. README and source code. Godoc.

Comparison with...

certbot: A heavyweight Python implementation which is a bit too “magic” for
my tastes. Tries to mutate your webserver configuration automatically.

acmetool is a single-file binary which only depends on basic system libraries
(on Linux, these are libc, libpthread, libcap, libattr). It doesn't do anything
to your webserver; it just places certificates at a standard location and can
also reload your webserver (whichever webserver it is) by executing hook shell

acmetool isn't based around individual transactions for obtaining certificates;
it's about satisfying expressed requirements by any means necessary. Its
comprehensible, magic-free state directory makes it as stateless and idempotent
as possible.

lego: Like acmetool, xenolf/lego provides
a library and client utility. The utility provides commands for creating
certificates, but doesn't provide a compelling system for managing the lifetime
of the short-lived certificates offered by Let's Encrypt. The user is expected
to generate and install all certificates manually.

diafygi/gethttpsforfree provides
an HTML file which uses JavaScript to make requests to an ACME server and
obtain certificates. It's a functional user interface, but like lego it
provides no answer for the automation issue, and is thus impractical given the
short lifetime of certificates issued by Let's Encrypt.

Comparison, list of client implementations

Automatic renewalYesNot yetNoNo
SAN supportYesYesYesYes
ECC supportYesNoNoNo
OCSP Must Staple supportYesNoNoNo
Revocation supportYesYesYesNo
State managementYes†Yes——
Single-file binaryYesNoYesYes
Quickstart wizardYesYesNoNo
Modifies webserver configNoBy defaultNoNo
Non-root supportOptionalOptionalOptional—
Supports ApacheYesYes——
Supports nginxYesExperimental——
Supports HAProxyYesNo——
Supports HitchYesNo——
Supports any web serverYesWebroot‡——
Authorization via webrootYesYes—Manual
Authorization via port 80 redirectorYesNoNoNo
Authorization via proxyYesNoNoNo
Authorization via listener§YesYesYesNo
Authorization via DNSHook onlyNoYesNo
Authorization via custom hookYesNoNoNo
Import state from official clientYes———
Windows (basic) supportNoNoYes—
Windows integration supportNoNoNo—

† acmetool has a different philosophy to state management and configuration to
the Let's Encrypt client; see the beginning of this README.

‡ The webroot method does not appear to provide any means of reloading the
webserver once the certificate has been changed, which means auto-renewal
requires manual intervention.

§ Requires downtime.

This table is maintained in good faith; I believe the above comparison to be
accurate. If notified of any inaccuracies, I will rectify the table and publish
a notice of correction here:

Documentation & Support

For more documentation see:
- User Guide
- Troubleshooting
- manpage

If your question or issue isn't resolved by any of the above, file an issue.

IRC: #acmetool on Freenode (webchat).

© 2015—2019 Hugo Landau <[email protected]>    MIT License

Licenced under the licence with SHA256 hash
fd80a26fbb3f644af1fa994134446702932968519797227e07a1368dea80f0bc, a copy of
which can be found