The RabbitMQ docs state ([1]):
RabbitMQ nodes and CLI tools (e.g. rabbitmqctl) use a cookie to
determine whether they are allowed to communicate with each
other. [...] The cookie is just a string of alphanumeric
characters up to 255 characters in size. It is usually stored in a
local file.
...and goes on to state (emphasis ours):
If the file does not exist, Erlang VM will try to create one with
a randomly generated value when the RabbitMQ server starts
up. Using such generated cookie files are **appropriate in
development environments only.**
The auto-generated cookie does not use cryptographic sources of
randomness, and generates 20 characters of `[A-Z]`. Because of a
semi-predictable seed, the entropy of this password is thus less than
the idealized 26^20 = 94 bits of entropy; in actuality, it is 36 bits
of entropy, or potentially as low as 20 if the performance of the
server is known.
These sizes are well within the scope of remote brute-force attacks.
On provision, install, and upgrade, replace the default insecure
20-character Erlang cookie with a cryptographically secure
255-character string (the max length allowed).
[1] https://www.rabbitmq.com/clustering.html#erlang-cookie
5c450afd2d, in ancient history, switched from `check_call` to
`check_output` and throwing away its result.
Use check_call, so that we show the steps to (re)starting the server.
This is required in order to lock down the RabbitMQ port to only
listen on localhost. If the nodename is `rabbit@hostname`, in most
circumstances the hostname will resolve to an external IP, which the
rabbitmq port will not be bound to.
Installs which used `rabbit@hostname`, due to RabbitMQ having been
installed before Zulip, would not have functioned if the host or
RabbitMQ service was restarted, as the localhost restrictions in the
RabbitMQ configuration would have made rabbitmqctl (and Zulip cron
jobs that call it) unable to find the rabbitmq server.
The previous commit ensures that configure-rabbitmq is re-run after
the nodename has changed. However, rabbitmq needs to be stopped
before `rabbitmq-env.conf` is changed; we use an `onlyif` on an `exec`
to print the warning about the node change, and let the subsequent
config change and notify of the service and configure-rabbitmq to
complete the re-configuration.
`/etc/rabbitmq/rabbitmq-env.conf` sets the nodename; anytime the
nodename changes, the backing database changes, and this requires
re-creating the rabbitmq users and permissions.
Trigger this in puppet by running configure-rabbitmq after the file
changes.
This addresses the problems mentioned in the previous commit, but for
existing installations which have `authenticator = standalone` in
their configurations.
This reconfigures all hostnames in certbot to use the webroot
authenticator, and attempts to force-renew their certificates.
Force-renewal is necessary because certbot contains no way to merely
update the configuration. Let's Encrypt allows for multiple extra
renewals per week, so this is a reasonable cost.
Because the certbot configuration is `configobj`, and not
`configparser`, we have no way to easily parse to determine if webroot
is in use; additionally, `certbot certificates` does not provide this
information. We use `grep`, on the assumption that this will catch
nearly all cases.
It is possible that this will find `authenticator = standalone`
certificates which are managed by Certbot, but not Zulip certificates.
These certificates would also fail to renew while Zulip is running, so
switching them to use the Zulip webroot would still be an improvement.
Fixes#20593.
Installing certbot with --method=standalone means that the
configuration file will be written to assume that the standalone
method will be used going forward. Since nginx will be running,
attempts to renew the certificate will fail.
Install a temporary self-signed certificate, just to allow nginx to
start, and then follow up (after applying puppet to start nginx) with
the call to setup-certbot, which will use the webroot authenticator.
The `setup-certbot --method=standalone` option is left intact, for use
in development environments.
Fixes part of #20593; it does not address installs which were
previously improperly configured with `authenticator = standalone`.
As a consequence:
• Bump minimum supported Python version to 3.7.
• Move Vagrant environment to Debian 10, which has Python 3.7.
• Move CI frontend tests to Debian 10.
• Move production build test to Debian 10.
Signed-off-by: Anders Kaseorg <anders@zulip.com>
On a system where ‘apt-get update’ has never been run, ‘apt-cache
policy’ may show no repositories at all. Try to correct this with
‘apt-get update’ before giving up.
Signed-off-by: Anders Kaseorg <anders@zulip.com>
The certbot package installs its own systemd timer (and cron job,
which disabled itself if systemd is enabled) which updates
certificates. This process races with the cron job which Zulip
installs -- the only difference being that Zulip respects the
`certbot.auto_renew` setting, and that it passes the deploy hook.
This means that occasionally nginx would not be reloaded, when the
systemd timer caught the expiration first.
Remove the custom cron job and `certbot-maybe-renew` script, and
reconfigure certbot to always reload nginx after deploying, using
certbot directory hooks.
Since `certbot.auto_renew` can't have an effect, remove the setting.
In turn, this removes the need for `--no-zulip-conf` to
`setup-certbot`. `--deploy-hook` is similarly removed, as running
deploy hooks to restart nginx is now the default; pass
`--no-directory-hooks` in standalone mode to not attempt to reload
nginx. The other property of `--deploy-hook`, of skipping symlinking
into place, is given its own flog.
We've had a number of unhappy reports of upgrades failing due to
webpack requiring too much memory. While the previous commit will
likely fix this issue for everyone, it's worth improving the error
message for failures here.
We avoid doing the stop+retry ourselves, because that could cause an
outage in a production system if webpack fails for another reason.
Fixes#20105.
Since the upgrade to Webpack 5, we've been seeing occasional reports
that servers with roughly 4GiB of RAM were getting OOM kills while
running webpack.
Since we can't readily optimize the memory requirements for webpack
itself, we should raise the RAM requirements for doing the
lower-downtime upgrade strategy.
Fixes#20231.
scripts.lib.node_cache expects Yarn to be in /srv/zulip-yarn, so if
it’s installed somewhere else, even if it’s the right version, we need
to reinstall it.
Signed-off-by: Anders Kaseorg <anders@zulip.com>
It recently started failing on Debian 10 (buster). We immediately
follow this by replacing these packages with our own versions from
pip.txt, anyway.
Signed-off-by: Anders Kaseorg <anders@zulip.com>
The support for bullseye was added in #17951
but it was not documented as bullseye was
frozen and did not have proper configuration
files, hence wasn't documented.
Since now bullseye is released as a stable
version, it's support can be documented.
The usual output from this command looks like
Notice: Compiled catalog for localhost in environment production in 2.33 seconds
Notice: /Stage[main]/Zulip::Apt_repository/Exec[setup_apt_repo]/returns: current_value 'notrun', should be ['0'] (noop)
Notice: Class[Zulip::Apt_repository]: Would have triggered 'refresh' from 1 event
Notice: Stage[main]: Would have triggered 'refresh' from 1 event
Notice: Applied catalog in 1.20 seconds
which doesn’t seem abnormally alarming, and hiding it makes failures
harder to diagnose.
Signed-off-by: Anders Kaseorg <anders@zulip.com>
These changes are all independent of each other; I just didn’t feel
like making dozens of commits for them.
Signed-off-by: Anders Kaseorg <anders@zulip.com>
Nonexistent processes and groups passed to `supervisortctl status` are
printed to STDOUT as follows:
```
$ supervisorctl status zulip-django nonexistent-process nonexistent-group:*
nonexistent-process: ERROR (no such process)
nonexistent-group: ERROR (no such group)
zulip-django RUNNING pid 16043, uptime 17:31:31
```
On supervisor 4 and above, this exits with an exit code of 4;
previously, it returned exit code 0. Ubuntu 18.04 has version 3.3.1,
and Ubuntu 20.04 has version 4.1.0.
Skip any lines with `ERROR (no such ...)`, and accept exit code 4 from
`supervisorctl status`.
This parameter is somewhat useful, and adding this also fixes a
regression where purge-old-deployments would crash since the changes
around c5580607a7 because of
inconsistent supported args lists.
Fixes#16659.
If the server is behind a reverse proxy with http_only=True, the
requests made by email-mirror-postfix need to use http, as https
doesn't work.
Staging and other hosts that are `zulip::app_frontend_base` but not
`zulip::app_frontend_once` do not have a
/etc/supervisor/conf.d/zulip/zulip-once.conf and as such do not have
`zulip_deliver_scheduled_emails` or `zulip_deliver_scheduled_messages`
and thus supervisor will fail to reload.
Making the contents of `zulip-workers` contingent on if the server is
_also_ a `-once` server is complicated, and would involve using Concat
fragments, which severely limit readability.
Instead, expel those two from `zulip-workers`; this is somewhat
reasonable, since they are use an entirely different codepath from
zulip_events_*, using the database rather than RabbitMQ for their
queuing.
This commit will allow us to pass the arguments in the
'clean...' functions when calling the `main` function (in
`provision`). It also changes args parsing
function location to `if __name__ == "__main__"` block as
we wouldn't need it to parse args when we call the
function.
We convert the `clean-unused-caches` script to a
python file so we can run it in provision by importing it
instead of running the script, hence saving some time.
Appending data back-to-back without serializing it loses the
information about where the breaks between them lie, which can lead to
different inputs having the same hash.
Using puppet modules from the puppet forge judiciously will allow us
to simplify the configuration somewhat; this specifically pulls in the
stdlib module, which we were already using parts of.
This moves the `.asc` files into subdirectories, and writes out the
according `.list` files into them. It moves from templates to
written-out `.list` files for clarity and ease of
implementation (Debian and Ubuntu need different templates for
`zulip`), and as a way of making explicit which releases are supported
for each list. For the special-case of the PGroonga signing key, we
source an additional file within the directory.
This simplifies the process for adding another class of `.list` file.
Add support for custom database names and database users, which can be
set with the `--postgresql-database-name` and
`--postgresql-database-user` install script options. If these
parameters aren't provided, then the defaults remain "zulip".
Fixes#17662.
Co-authored-by: Alex Vandiver <alexmv@zulip.com>
Add a helper `run_psql_as_postgres` function in
`scripts/lib/zulip_tools.py`. This is preparatory refactoring for the
work to add custom database and user names.
Fixes this error when running the installer from a directory that
isn’t world-readable:
+ su zulip -c 'git config --global user.email anders@zulip.com'
fatal: cannot come back to cwd: Permission denied
Signed-off-by: Anders Kaseorg <anders@zulip.com>
When upgrading from a pre-4.0 release, scripts/stop-server logic would
check whether supervisord configuration files were present to
determine what it needed to restart, but only considered paths to
those files that are introduced in Zulip 4.0.
Fixed#18493.
This ensures that the `git describe` queries that we run for caching
Zulip's Git version are guaranteed to include recent releases.
This change ensures that we have accurate output even if we're pointed
at a fork of Zulip that never updates its tags.
Additionally, it will make it possible to record the
`git merge-base upstream/master` in future commits.
Note that because we run this code before unpacking the new version,
the pre-upgrade version of this code runs.
As a result, we cannot assume that the upstream repository exists.
This removes a possible window where an installer error could leave
`nvm` in a state where it had prepended the full path to the
newly-installed `npm` to `$PATH`; we would like to avoid `nvm`
fiddling with path whenever possible (ref ebe930ab2c).
During the upgrade process of a postgresql-only Zulip installation,
(`puppet_classes = zulip::profile::postgresql` in
`/etc/zulip/zulip.conf`) either `scripts/start-server` or
`scripts/stop-server` fail because they try to handle supervisor
services that are not available (e.g. Tornado) since only
`/etc/supervisor/conf.d/zulip/zulip_db.conf` is present and not
`/etc/supervisor/conf.d/zulip/zulip.conf`.
While this wasn't previously supported, it's a pretty reasonable thing
to do, and can be readily supported by just adding a few conditionals.
Thumbor and tc-aws have been dragging their feet on Python 3 support
for years, and even the alphas and unofficial forks we’ve been running
don’t seem to be maintained anymore. Depending on these projects is
no longer viable for us.
Signed-off-by: Anders Kaseorg <anders@zulip.com>
The `en_US.UTF-8` locale may not be configured or generated on all
installs; it also requires that the `locales` package be installed.
If users generate the `en_US.UTF-8` locale without adding it to the
permanent set of system locales, the generated `en_US.UTF-8` stops
working when the `locales` package is updated.
Switch to using `C.UTF-8` in all cases, which is guaranteed to be
installed.
Fixes#15819.
In some cases, puppet can end up restarting supervisord services - which
will use code from the old deployment, because when puppet runs,
/home/zulip/deployments/current still points there. Thus restart-server
needs to be used in favor of start-server, unless we know that puppet
has been skipped.
Previous versions of zulip used `nvm alias default ...` to have `nvm`
prepend the full path to the latest `node` install to the `PATH` in
root's shell. Unfortunately, this means that `update-prod-static`,
when called from `upgrade-zulip-stage-2` after an upgrade of node in
`install-node`, would still have the full path to the _old_ `node` at
the start of its PATH, because the PATH of `upgrade-zulip-stage-2`
would still be unchanged.
Bootstrap out of this by setting a known-reasonable PATH during
upgrade, and remove the problematic `nvm alias default` behaviour.
Fixes#18258.
In Debian, becoming root as `su` does not alter the `$PATH`; this can
lead to the root user not having `/usr/sbin` in its path, and thus
the `useradd zulip` step of the installer fails.
Fixes#17441.
This commit removes redundant yarn cache by removing the old
version directories, i.e. All the directory under `~/.cache/yarn`
except `~/.cache/yarn/v6` (current version directory).
Fixes#15964.
The path which contains all of the Zulip supervisor files changed in
3ab9b31d2f to make it easier to purge
now-unwanted supervisor configuration files. However, the paths that
the zulip upgrade process, and restart-server, look at were not
adjusted.
Fix the supervisor configuration file paths.
3314fefaec started needing `python3-yaml`, but incorrectly claimed
that it was always an indirect dependency; it is a dependency of
`ubuntu-minimal` on 20.04, but not required on 18.04 or Debian. We
cannot install it in puppet because then is definitionally too late;
it is needed at load time by `zulip-puppet-apply`.
Install `python3-yaml`, but guarded by a simple check so as to not
further slow most installs.
Fixes#18179.
The stacktraces here are seldom useful -- for the calls to
upgrade-stage-2, we know precisely what was run. For the `run`
wrapper, the output contains the command that failed, which is
sufficient to identify where in the upgrade process it was. Showing
more stacktrace below the actual error merely confuses users and
scrolls the real error off of the screen.
For installs which use the `upgrade-zulip-from-git` process, the
deployment directory is a git checkout. This means that an
administrator can, as an emergency tool, run `git revert` and similar
commands -- assuming there is a `~/.gitconfig` set up for the zulip
user.
Add commands to `scripts/lib/install` to create a `~/.gitconfig` file
at installation time. The `user.name` and `user.email` fields are set
to the hostname and passed-in `--email` value, respectively.
Fixes#18039.
0663b23d54 changed zulip-puppet-apply to
use the venv, because it began using `yaml` to parse the output of
puppet to determine if changes would happen.
However, not every install ends with a venv; notably, non-frontend
servers do not have one. Attempting to run zulip-puppet-apply on them
hence now fails.
Remove this dependency on the venv, by installing a system
python3-yaml package -- though in reality, this package is already an
indirect dependency of the system. Especially since pyyaml is quite
stable, we're not using it in any interesting way, and it does not
actually add to the dependencies, it is preferable to parsing the YAML
by hand in this instance.
When exception is raised inside an exception handler, Python 3
helpfully prints both tracebacks separated by “During handling of the
above exception, another exception occurred:”. But when we’re using
an exception handler to retry the same operation, multiple tracebacks
are just noise. Suppress the earlier one using PEP 409 syntax.
Signed-off-by: Anders Kaseorg <anders@zulip.com>
This means that in steady-state, `zulip-puppet-apply` is expected to
produce no changes or commands to execute. The verification step of
`setup-apt-repo` is quite fast, so this cleans up the output for very
little cost.
The class names need to be renamed even if we are not about to run
puppet ourselves; otherwise, deployments which rely on running puppet
themselves will still have the wrong class names.
These are respected by `urllib`, and thus also `requests`. We set
`HTTP_proxy`, not `HTTP_PROXY`, because the latter is ignored in
situations which might be running under CGI -- in such cases it may be
coming from the `Proxy:` header in the request.
Using `config_file.write()` only writes out what python stored of the
file; as such, it strips all comments and whitespace.
Use `crudini --set`, which only modifies the line whose contents are
changed.
There is only one PostgreSQL database; the "appdb" is irrelevant.
Also use "postgresql," as it is the name of the software, whereas
"postgres" the name of the binary and colloquial name. This is minor
cleanup, but enabled by the other renames in the previous commit.
The "voyager" name is non-intuitive and not significant.
`zulip::voyager` and `zulip::dockervoyager` stubs are kept for
back-compatibility with existing `zulip.conf` files.
This moves the puppet configuration closer to the "roles and profiles
method"[1] which is suggested for organizing puppet classes. Notably,
here it makes clear which classes are meant to be able to stand alone
as deployments.
Shims are left behind at the previous names, for compatibility with
existing `zulip.conf` files when upgrading.
[1] https://puppet.com/docs/pe/2019.8/the_roles_and_profiles_method
Fingerprinting the config is somewhat brittle -- it requires either
custom bootstrapping for old (fingerprint-less) configs, and may have
false-positives.
Since generating the config is lightweight, do so into the .tmp files,
and compare the output to the originals to determine if there are
changes to apply.
In order to both surface errors, as well as notify the user in case a
restart is necessary, we must run it twice. The `onlyif`
functionality cannot show configuration errors to the user, only
determine if the command runs or not. We thus run the command once,
judging errors as "interesting" enough to run the actual command,
whose failure will be verbose in Puppet and halt any steps that depend
on it.
Removing the `onlyif` would result in `stage_updated_sharding` showing
up in the output of every Puppet run, which obscures the important
messages it displays when an update to sharding is necessary.
Removing the `command` (e.g. making it an `echo`) would result in
removing the ability to report configuration errors. We thus have no
choice but to run it twice; this is thankfully low-overhead.
The reason higher expected_time_to_clear_backlog were allowed for queues
during "bursts" was, in simpler terms, because those queues to which
this happens, intrinsically have a higher acceptable "time until cleared"
for new events. E.g. digests_email, where it's completely fine to take a
long time to send them out after putting in the queue. And that's
already configurable without a normal/burst distinction.
Thanks to this we can remove a bunch of overly complicated, and
ultimately useless, logic.
The race condition is described in the comment block removed by this
commit. This leaves room for another, remaining race condition
that should be virtually impossible, but nevertheless it seems
worthwhile to have it documented in the code, so we put a new comment
describing it.
As a final note, this is not a new race condition,
it was hypothetically possible with the old code as well.
We can compute the intended number of processes from the sharding
configuration. In doing so, also validate that all of the ports are
contiguous.
This removes a discrepancy between `scripts/lib/sharding.py` and other
parts of the codebase about if merely having a `[tornado_sharding]`
section is sufficient to enable sharding. Having behaviour which
changes merely based on if an empty section exists is surprising.
This does require that a (presumably empty) `9800` configuration line
exist, but making that default explicit is useful.
After this commit, configuring sharding can be done by adding to
`zulip.conf`:
```
[tornado_sharding]
9800 = # default
9801 = other_realm
```
Followed by running `./scripts/refresh-sharding-and-restart`.
This supports running puppet to pick up new sharding changes, which
will warn of the need to finalize them via
`refresh-sharding-and-restart`, or simply running that directly.
The value in the stats file can get outdated if the queue hasn't done
enough iterations to update the stats file for a while. The queue size
output by rabbitmqctl list_queues is more up to date, and empirically
tends to agree with the value in the stats file (when the stats file is
fresh).
This will let PyYAML link against LibYAML when PyYAML is next
installed. Due to virtualenv-clone, that won’t happen until the next
Python package removal anyway, so we don’t bother bumping
PROVISION_VERSION.
Signed-off-by: Anders Kaseorg <anders@zulip.com>
The combination of `--force --noop` is potentially confusing, but
currently `--noop` makes no sense without `--force`, as it will prompt
and then not make changes.
Make `--noop` skip the prompt as well.
Fixes#12868.
We now also include python version in the format
'major.minor.patchlevel', when generating hash for a
requirement file. This was necessary since packages tend to
break on different versions of python, so it is important to
track the version on which the venv was setup.
WARN: This commit will force all zulip venvs to be recreated.
We were already using packages names along with their versions
to generate hash for the requirement file, as we were passing
the `.txt` files to the hash_reqs file instead of intended `.in` files
for which the functions in this file was originially designed.
Changed the expand_reqs_helper function to adapt for the `.txt` files.
Although mktemp is deprecated due to security issues, this is not a
security issue.
The security problems with mktemp happen when you open the resulting
filename (without O_EXCL) in a publicly writable directory, because
then someone else might have predicted the filename and created or
symlinked or hardlinked something there between the mktemp and the
open, causing you to write to a file you didn’t expect.
Here we don’t open the resulting filename, we symlink to it. symlink
will refuse to clobber an existing file, and we handle the error that
arises from this case. This is the normal way to atomically create a
symlink.
We should still replace mktemp because it’s deprecated, but we can’t
replace it with a function that creates the temporary file. Instead
we build a random filename ourselves.
Signed-off-by: Anders Kaseorg <anders@zulip.com>
Otherwise, the useradd command will fail during the DigitalOcean
1-Click App installation because the install script is called
twice during the whole process. Plus the Zulip install script
is designed to be idempotent and this bug compromises that.
The value is a holdover from when it controlled runtime behavior,
which it no longer does.
Stop taking a DEPLOYMENT_TYPE, which is unused; the python code only
care about if the option exists, not its value.
These are more correct to the sense of "is this a service we
configured for Zulip", and removes potential confusion around the 0/1
values being backwards from how binary is usually interpreted.
Using checks of `,$PUPPET_CLASSES,` is repetitive and error-prone; it
does not properly deal with `zulip_ops::` classes, for instance, which
include the `zulip::` classes.
As alluded to in ca9d27175b, this can be fixed by inspecting the
classes that would be applied, using `puppet --write-catalog-summary`.
We work around the chicken-and-egg problem alluded to therein by
writing out as complete `zulip.conf` as would be necessary, before
running puppet and removing the sections we then know to not be
needed.
Unfortunately, there are two checks for `$PUPPET_CLASSES` which cannot
be switched to this technique, as they concern errors that we wish to
catch quite early, and thus before we have puppet installed. Since we
expect failures of those to only concern warnings, and only be
mistakenly omitted for internal `zulip_ops::` classes, this seems a
reasonable risk to admit in exchange for catching common errors early.
When supervisor is first installed, it is started automatically, and
creates the socket, owned by root. Subsequent reconfiguration in
puppet only calls `reread + update`, which is insufficient to apply
the `chown = zulip:zulip` line in `supervisord.conf`, leaving the
socket owned by `root` and the last part of the installation unable to
restart `supervisor` services as the `zulip` user. The `chown` line
in `scripts/lib/install` exists to paper over this.
Add a separate exec target for changes to `supervisord.conf` itself,
which restarts the full service. This leaves the default `restart`
action on the service for the lightweight `reread + update` action,
which is more common.
We use `systemctl` only on redhat-esque builds, because CI runs
Ubuntu, but init is not systemd in that context. `systemctl reload`
is sufficient to re-apply the socket ownership, but a full `restart`
and not `reload` is necessary under `/etc/init.d/supervisor`.
49a7a66004 and immediately previous commits began installing
PostgreSQL 12 from their apt repository. On machines which already
have the distribution-provided version of PostgreSQL installed,
however, this leads to failure to apply puppet when restarting
PostgreSQL 12, as both attempt to claim the same port.
During installation, if we will be installing PostgreSQL, look for
other versions than what we will install, and abort if they are
found. This is safer than attempting to automatically uninstall or
reconfigure existing databases.
This allows for installing from-scratch with a different pinned
version of PostgreSQL, and provides a single place to change when the
default should increase.
Using `/etc/init.d/postgresql` as the detection of if Postgres is on
the server is incorrect, because this line runs _before_ puppet and
any packages are installed. Thus, it cannot tell the difference
between a new Ubuntu one-host first-time-install without PostgreSQL
yet, and one which is merely a front-end and will never have
PostgreSQL. This leads to failures in first-time installs:
```
Error: Evaluation Error: Error while evaluating a Function Call,
Could not find template 'zulip/postgresql//postgresql.conf.template.erb'
```
The only way to detect if PostgreSQL will be present in the _end_
state of the install is to examine the puppet classes that are
applied.
To do this, we must inspect `PUPPET_CLASSES`. Unfortunately, this can
be fragile to subclassing (e.g. `zulip_ops::postgres_appdb`). We
might desire to use `puppet apply --write-catalog-summary` to deduce
the _applied_ classes, which would unroll the inheritance; however,
this causes a chicken-and-egg problem, because `zulip.conf` must be
already written out (including a value for `postgresql.version`, if
necessary!) before such a puppet run could successfully complete.
Switch to predicating the `postgresql.version` key on the puppet
classes that are known to install postgres.
Support for Xenial and Stretch was removed (5154ddafca, 0f4b1076ad,
8944e0ad53, 79acd5ae40, 1219a2e854), but not all codepaths were
updated to remove their conditionals on it.
Remove all code predicated on Xenial or Stretch. debathena support
was migrated to Bionic, since that appears to be the current state of
existing debathena servers.
0f4b1076ad removed Ubuntu 16.04 "xenial" and Debian 9 "stretch" from
the printed list of supported operating systems, but left them in the
verification check that controls if that message is printed,
effectively continuing to support them.
Conversely, 439f0d3004 added Ubuntu 20.04 "focal" to the check, but
not to the printed list.
Synchronize to check and print the right supported distributions:
Ubuntu 18.04 "bionic", Ubuntu 20.04 "focal", and Debian 10 "buster".
The previous commit removed the only behavior difference between the
two flags; both of them skip user/database creation, and the tables
therein.
Of the two options `--no-init-db` is more explicit as to what it does,
as opposed to just one facet of when it might be used; remove
`--remote-postgres`.
Since `--postgres-missing-dictionaries` edits `/etc/zulip/zulip.conf`,
it interferes with the intent of `--no-overwrite-settings`.
Make the two settings conflict, to prevent this unclear state.