User:Paul/sandbox/OpenBSD Basic Server

OpenBSD has earned its reputation as a BSD descendant focused on security. With the increased development of OpenBSD's httpd and OpenSMTPD, plus most of the components commonly used in a basic web server, OpenBSD provides a highly secure and efficient choice for building servers.

Finding online support for OpenBSD can be much more difficult when compared to Linux. While the OpenBSD project requires its man pages to be very complete, support beyond man pages such as tutorials or sample configurations can be much harder to find. This has largely been due to the project being targeted at use primarily by professional systems administrators.

This tutorial will establish a basic web server that includes a functioning mail server with local maildir accessed through mutt.

Notable differences from Ubuntu Linux

Shell

Ubuntu default shell uses Bash (BASH) while OpenBSD uses KornShell (ksh).

ll (ls -alF)

Ubuntu has a convenient command, ll, for viewing directory contents that is a shortcut for ls -alF.

To add ll to the OpenBSD command line:

$ nano .profile

Add the following line:

alias ll="ls -alF"

Default editor

The default text editor in OpenBSD is vi. To change to a different default text editor:

$ nano .profile

Add the following line:

export EDITOR=/usr/local/bin/nano

Do the same for root:

$ doas nano /root/.kshrc

Add the following line:

export EDITOR=/usr/local/bin/nano

Note that this does not change the default editor for doas, such as when calling the crontab command.

Web server

Most of the instructions in this article require root:

$ doas su

OpenBSD comes with httpd, the project's own web server, installed by default though disabled. The httpd configuration is managed in its configuration file, /etc/httpd.conf, which has to be created:

# nano /etc/httpd.conf

Add to the file:

# Main Configuration
server "example.com" {
    listen on * port 80
    root "/htdocs/example.com"
    location "/.well-known/acme-challenge/*" {
        root "/acme"
        request strip 2
    }
    location * {
        block return 302 "https://$HTTP_HOST$REQUEST_URI"
    }
}

Test the configuration:

# httpd -n
configuration OK

Start httpd.

# rcctl -f start httpd
httpd(ok)

Add a Let's Encrypt certificate to the server:

# cp /etc/examples/acme-client.conf /etc/acme-client.conf
# nano /etc/acme-client.conf

Change example.com to the desired domain and remove, change, or add subdomains to the alternative line.

# acme-client -v example.com

After successful registration, create a cron job:

# crontab -e

Add:

0	*	*	*	*	sleep $((RANDOM \% 2048)) && \
	acme-client example.com && rcctl reload httpd

Now add the SSL/TLS and redirect options httpd.conf

# nano /etc/httpd.conf

Add:

# This is a redirect to the Main Configuration
server "www.example.com" {
    listen on * port 80
    listen on * tls port 443
    tls {
        certificate "/etc/ssl/example.com.fullchain.pem"
        key "/etc/ssl/private/example.com.key"
    }
    block return 301 "http://example.com$REQUEST_URI"
}
 
server "example.com" {
    listen on * tls port 443
    root "/htdocs/example.com"
    tls {
        certificate "/etc/ssl/example.com.fullchain.pem"
        key "/etc/ssl/private/example.com.key"
    }

    location "/.well-known/acme-challenge/*" {
        root "/acme"
        request strip 2
    }
}

Test and restart httpd

# httpd -n
Configuration OK
# rcctl reload httpd
httpd(ok)

Email

OpenBSD in its default configuration comes with opensmtpd in a very secure configuration that supports outgoing mail. This is primarily useful for transactional email, most especially administrative messages.

Administrative message recipients can be configured in the aliases file and are default configured to be sent to the local root user local mailbox. To configure additional recipients:

# nano /etc/mail/aliases

Change and add:

# Basic system aliases -- these MUST be present
MAILER-DAEMON: postmaster
postmaster: root
root: username@example.com,anotherusername@example.net

Update the configuration:

# newaliases

Mail server configuration

Create DKIM key and directory:

# mkdir /etc/mail/dkim
# openssl genrsa -out /etc/mail/dkim/example.com.key 1024
# chmod 640 /etc/mail/dkim/example.com.key
# openssl rsa -in /etc/mail/dkim/example.com.key -pubout -out /etc/mail/dkim/example.com.pub
# cat /etc/mail/dkim/example.com.pub

Install and configure antispam packages

# pkg_add redis rspamd opensmtpd-filter-rspamd opensmtpd-filter-senderscore

Configure DKIM signing:

# chown root:_rspamd /etc/mail/dkim/example.com.key
# mkdir /etc/rspamd/local.d
# nano /etc/rspamd/local.d/dkim_signing.conf
allow_username_mismatch = true;

domain {
    example.com {
        path = "/etc/mail/dkim/example.com.key";
        selector = "20200221";
    }
}

Enable and start redis and rspamd:

# rcctl enable redis
# rcctl enable rspamd
# rcctl start redis
redis(ok)
# rcctl start rspamd
rspamd(ok)

Update the OpenSMTPD configuration:

# mv /etc/mail/smtpd.conf /etc/mail/smtpd.conf.original
# nano /etc/mail/smtpd.conf

pki mail.hypno.cat cert "/etc/ssl/mail.hypno.cat.fullchain.pem"
pki mail.hypno.cat key "/etc/ssl/private/mail.hypno.cat.key"

filter check_dyndns phase connect match rdns regex { '.*\.dyn\..*', '.*\.dsl\..*' } \
    disconnect "550 no residential connections"

filter check_rdns phase connect match !rdns \
    disconnect "550 no rDNS is so 80s"

filter check_fcrdns phase connect match !fcrdns \
    disconnect "550 no FCrDNS is so 80s"

filter senderscore \
    proc-exec "filter-senderscore -blockBelow 10 -junkBelow 70 -slowFactor 5000"

filter rspamd proc-exec "filter-rspamd"

table aliases file:/etc/mail/aliases

listen on all tls pki example.com \
    filter { check_dyndns, check_rdns, check_fcrdns, senderscore, rspamd }

listen on all port submission tls-require pki example.com auth filter rspamd

action "local_mail" maildir junk alias <aliases>
action "outbound" relay helo example.com

match from any for domain "example.com" action "local_mail"
match for local action "local_mail"

match from any auth for any action "outbound"
match for any action "outbound"