mattermost is an online collaboration server, featuring chatting,
online calls, VCS integration, and much more.

It relies on PostgreSQL, which is a run-time dependency.

It is also famous for its "matterbridge" bridge infrastructure.

By default mattermost is running on http://localhost:8065

You need to create a new user/group for this script to run
groupadd -g 394 mattermost"
useradd -u 394 -g 394 -d /opt/mattermost mattermost"

A basic setup with local-only postgres 14 is the following:

1. install postgresql (14 should work)
2. init postgres db:
su postgres -c "initdb -D /var/lib/pgsql/14/data \
--locale=en_US.UTF-8 -A md5 -W"
3. set some password, say "password"
4. /etc/rc.d/rc.postgresql start
4.1 echo  "/etc/rc.d/rc.postgresql start" >> /etc/rc.d/rc.local
5. PGPASSWORD=password psql -U postgres -S postgres -c\
"create user mmuser with password 'mmpassword';"
6. PGPASSWORD=password psql -U postgres -S postgres -c\
"CREATE DATABASE mattermost WITH ENCODING 'UTF8' \
LC_COLLATE='en_US.UTF-8' LC_CTYPE='en_US.UTF-8' \
TEMPLATE=template0;"
7. PGPASSWORD=password psql -U postgres -S postgres -c\
"GRANT ALL PRIVILEGES ON DATABASE mattermost to mmuser;"
8. setup mattermost config file
/opt/mattermost/config/config.json

The init script rc.mattermost is a bit improvised, do not expect too
much of it.