On 10/17/2025 3:09 AM, Stephen J. Turnbull wrote:
dap1--- via Mailman-users writes:

  > I am about to migrate from mailma2 on CentOS to mailman3 on
  > Ubuntu. Are there any special gotchas of which I need to be aware?
  > TIA.

* The Ubuntu packages are old, and not well-supported by Ubuntu or the
Mailman project.  Mailman 3 is not a hyperactive project, but we are
making steady progress and many new Mailman 3 users have issues or
requests for enhancement for 2-, 3-year-old packages that have been
fixed or implemented in the most recent releases.  For these reasons,
we strongly recommend installing from source or from PyPI in a virtual
environment:
https://docs.mailman3.org/en/latest/install/virtualenv.html#virtualenv-install
(Installing from source is not hard, but it's more work than using
pre-built packages.  Source is required for beta testers and
developers, but not recommended for most production environments.)

* If your preferred RDBMS is in the MySQL family:
1.  Make sure the Mailman database(s) have the utf8mb4 charset option
     set.  Otherwise all emoji and some Asian characters will cause
     your database to throw errors (I think this is mostly an issue for
     HyperKitty and maybe a few users who put them in their display
     names in Postorius and Mailman core).  This is not needed for
     PostgreSQL or SQLite3.
2.  You may want to increase the timeout for startup (I think this is
     in the systemd units for mailman and mailmanweb).  The issue is
     that the mysqld doesn't exit until the journal has been flushed to
     the main database (or something like that), and this may take many
     seconds.  This is not an issue for SQLite3 (it's a library) or
     PostgreSQL (it uses dbus to notify systemd that it's ready).

* The migration scripts for list database and web databases are quite
good, but not 100%.

* The user model is completely different.  Ordinary subscribers will
probably be happy or won't notice, but there are some traps for
administration roles.  The most important is that some list owners
will give the owner password to moderators so they can do work like
use mass subscribe, but put them on the moderator list attribute so
they get the moderation notices.  These moderators will lose the
"owner" capabilities like mass subscribe.

* If you're looking at a multinode installation with Mailman core,
Postorius and HyperKitty distributed across several hosts or
containers, configuration can be finicky.  I don't recommend it unless
you're familiar with such distributed operations.

Steve

Hi Steve,

Thanks for the info. I thought I had followed everything but I an unable to start mailman3 because all the expected directories in /var are missing. What steps did I miss?

The instructions are a bit confusing because I had to keep switching between mailman and admin for setting up various files such as /etc/mailman3. There was no step to make mailman a sudoers. I hope I didn't mess up the installation by switching back and forth.

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