Name

lacme - ACME client written with process isolation and minimal privileges in mind

Synopsis

lacme [--config=FILENAME] [--socket=PATH] [OPTION …] COMMAND [ARGUMENT …]

Description

lacme is a small ACME client written with process isolation and minimal privileges in mind. It is divided into four components, each with its own executable:

  1. A lacme-accountd(1) process to manage the account key and issue SHA-256 signatures needed for each ACME command. (This process binds to a UNIX-domain socket to reply to signature requests from the ACME client.) One can use the UNIX-domain socket forwarding facility of OpenSSH 6.7 and later to run lacme-accountd(1) and lacme on different hosts. Alternatively, the lacme-accountd(1) process can be spawned by the “master” lacme process below; in that case, the two processes communicate through a socket pair.

  2. A “master” lacme process, which runs as root and is the only component with access to the private key material of the server keys. It is used to fork the ACME client (and optionally the ACME webserver) after dropping root privileges. For certificate issuances (newOrder command), it also generates Certificate Signing Requests, then verifies the validity of the issued certificate, and optionally reloads or restarts services when the notify option is set.

  3. An actual ACME client (specified with the command option of the [client] section of the configuration file), which builds ACME commands and dialogues with the remote ACME server. Since ACME commands need to be signed with the account key, the “master” lacme process passes the lacme-accountd(1) UNIX-domain socket to the ACME client: data signatures are requested by writing the data to be signed to the socket.

  4. For certificate issuances (newOrder command), an optional webserver (specified with the command option of the [webserver] section of the configuration file), which is spawned by the “master” lacme. (The only challenge type currently supported by lacme is http-01, which requires a webserver to answer challenges.) That webserver only processes GET and HEAD requests under the /.well-known/acme-challenge/ URI. Moreover temporary iptables(8) rules can be automatically installed to open the HTTP port.

Commands

lacme account [--tos-agreed] [--register] [CONTACT …]

Register (if --registered is set) a lacme-accountd(1)-managed account key. A list of CONTACT information (such as maito: URIs) can be specified in order for the ACME server to contact the client for issues related to this registration (such as notifications about server-initiated revocations). --tos-agreed indicates agreement with the ACME server’s Terms of Service (and might be required for registration).

If the account key is already registered, update the contact info with the given list of CONTACT information.

Upon success, lacme prints the new or updated Account Object from the ACME server.

lacme [--config-certs=FILE] [--min-days=INT] newOrder [SECTION …]

Read the certificate configuration FILE (see the certificate configuration file section below for the configuration options), and request new Certificate Issuance for each of its sections (or the given list of SECTIONs). Command alias: new-order.

lacme revokeCert FILE [FILE …]

Request that the given certificate(s) FILE(s) be revoked. For this command, lacme-accountd(1) can be pointed to either the account key or the server’s private key. Command alias: revoke-cert.

Generic options

--config=filename

Use filename as configuration file. See the configuration file section below for the configuration options.

--socket=path

Use path as the lacme-accountd(1) UNIX-domain socket to connect to for signature requests from the ACME client. lacme aborts if path is readable or writable by other users, or if its parent directory is writable by other users. This command-line option overrides the socket option of the [client] section of the configuration file. Moreover this option is ignored when the configuration file has an [accountd] section; in that case lacme spawns lacme-accountd(1), and the two processes communicate through a socket pair.

-h, --help

Display a brief help and exit.

-q, --quiet

Be quiet.

--debug

Turn on debug mode.

Configuration file

If --config= is not given, lacme uses the first existing configuration file among ./lacme.conf, $XDG_CONFIG_HOME/lacme/lacme.conf (or ~/.config/lacme/lacme.conf if the XDG_CONFIG_HOME environment variable is not set), and /etc/lacme/lacme.conf. Valid options are:

Default section

config-certs

For certificate issuances (newOrder command), specify the space-separated list of certificate configuration files or directories to use (see the certificate configuration file section below for the configuration options).

Paths not starting with / are relative to the directory name of the configuration filename. The list of files and directories is processed in order, with the later items taking precedence. Files in a directory are processed in lexicographic order, only considering the ones with suffix .conf.

Default: lacme-certs.conf lacme-certs.conf.d/.

[client] section

This section is used for configuring the ACME client (which takes care of ACME commands and dialogues with the remote ACME server).

socket

See --socket=. Default: $XDG_RUNTIME_DIR/S.lacme if the XDG_RUNTIME_DIR environment variable is set.

user

The username to drop privileges to (setting both effective and real uid). Preserve root privileges if the value is empty (not recommended). Default: nobody.

group

The groupname to drop privileges to (setting both effective and real gid, and also setting the list of supplementary gids to that single group). Preserve root privileges if the value is empty (not recommended). Default: nogroup.

command

Path to the ACME client executable. Default: /usr/lib/lacme/client.

server

Root URI of the ACME server. Default: https://acme-v02.api.letsencrypt.org/directory.

timeout

Timeout in seconds after which the client stops polling the ACME server and considers the request failed. Default: 10.

SSL_verify

Whether to verify the server certificate chain. Default: Yes.

SSL_version

Specify the version of the SSL protocol used to transmit data.

SSL_cipher_list

Specify the cipher list for the connection, see ciphers(1ssl) for more information.

[webserver] section

This section is used to configure how ACME challenge responses are served during certificate issuance.

listen

Comma- or space-separated list of addresses to listen on. Valid addresses are of the form IPV4:PORT, [IPV6]:PORT (where the :PORT suffix is optional and defaults to the HTTP port 80), or an absolute path of a UNIX-domain socket (created with mode 0666). Default: /var/run/lacme-www.socket.

Note: The default value is only suitable when an external HTTP daemon is publicly reachable and passes all ACME challenge requests to the webserver component through the UNIX-domain socket /var/run/lacme-www.socket (for instance using the provided /etc/lacme/apache2.conf or /etc/lacme/nginx.conf configuration snippets for each virtual host requiring authorization). If there is no HTTP daemon bound to port 80 one needs to set listen to [::] (or 0.0.0.0 [::] when dual IPv4/IPv6 stack is disabled or unavailable), and possibly also set iptables to Yes.

challenge-directory

Specify a non-existent directory under which an external HTTP daemon is configured to serve GET requests for challenge files under /.well-known/acme-challenge/ (for each virtual host requiring authorization) as static files. This option is required when listen is empty.

user

The username to drop privileges to (setting both effective and real uid). Preserve root privileges if the value is empty (not recommended). Default: www-data.

group

The groupname to drop privileges to (setting both effective and real gid, and also setting the list of supplementary gids to that single group). Preserve root privileges if the value is empty (not recommended). Default: www-data.

command

Path to the ACME webserver executable. A separate process is spawned for each address to listen on. (In particular no webserver process is forked when the listen option is empty.) Default: /usr/lib/lacme/webserver.

iptables

Whether to automatically install temporary iptables(8) rules to open the ADDRESS[:PORT] specified with listen. The rules are automatically removed once lacme exits. Default: No.

[accountd] section

This section is used for configuring the lacme-accountd(1) process. If the section (including its header) is absent or commented out, lacme connects to an existing UNIX-domain socket bound by a running lacme-accountd(1) process.

user

The username to drop privileges to (setting both effective and real uid). Preserve root privileges if the value is empty.

group

The groupname to drop privileges to (setting both effective and real gid, and also setting the list of supplementary gids to that single group). Preserve root privileges if the value is empty.

command

Path to the lacme-accountd(1) executable. Default: /usr/bin/lacme-accountd.

config

Path to the lacme-accountd(1) configuration file. Default: /etc/lacme/lacme-accountd.conf.

privkey

The (private) account key to use for signing requests. See lacme-accountd(1) for details.

quiet

Be quiet. Possible values: Yes/No.

Certificate configuration file

For certificate issuances (newOrder command), a separate file is used to configure paths to the certificate and key, as well as the subject, subjectAltName, etc. to generate Certificate Signing Requests. Each section denotes a separate certificate issuance. Valid options are:

certificate

Where to store the issued certificate (in PEM format). At least one of certificate or certificate-chain is required.

certificate-chain

Where to store the issued certificate, concatenated with the content of the file specified specified with the CAfile option (in PEM format). At least one of certificate or certificate-chain is required.

certificate-key

Path the service’s private key. This option is required. The following command can be used to generate a new 4096-bits RSA key in PEM format with mode 0600:

openssl genrsa 4096 | install -m0600 /dev/stdin /path/to/srv.key
min-days

For an existing certificate, the minimum number of days before its expiration date the section is considered for re-issuance. A negative value forces reissuance, while the number 0 limits reissuance to expired certificates. Default: the value of the CLI option --min-days, or 21 if there is no such option.

CAfile

Path to the issuer’s certificate. This is used for certificate-chain and to verify the validity of each issued certificate. Specifying an empty value skip certificate validation. Default: /usr/share/lacme/lets-encrypt-x3-cross-signed.pem.

hash

Message digest algorithm to sign the Certificate Signing Request with.

keyUsage

Comma-separated list of Key Usages, see x509v3_config(5ssl).

subject

Subject field of the Certificate Signing Request, in the form /type0=value0/type1=value1/type2=…. This option is required.

subjectAltName

Comma-separated list of Subject Alternative Names, in the form type0:value1,type1:value1,type2:… The only type currently supported is DNS, to specify an alternative domain name.

chown

An optional username[:groupname] to chown the issued certificate and certificate-chain to.

chmod

An optional octal mode to chmod the issued certificate and certificate-chain to.

notify

Command to pass the the system’s command shell (/bin/sh -c) after successful installation of the certificate and/or certificate-chain.

Examples

~$ sudo lacme account --register --tos-agreed mailto:noreply@example.com
~$ sudo lacme newOrder
~$ sudo lacme revokeCert /path/to/server/certificate.pem

See also

lacme-accountd(1)