Your LimeSurvey version: Community Edition Version 6.5.10+240603
Own server or LimeSurvey hosting: Own Server
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Our hosting partner is planning an update next week, and we would like to add a message for users (>300) so as respondents informing about possible downtime.

So far, I've only found maintenanceMode that isn’t supported in my LS version.

Any other ideas?

What exactly is your hosting partner updating? Their server environment or Limesurvey?

Updating Limesurvey (especially if they use comfort update) should talke about 5 minutes and during these 5 minutes Limesurvey is maybe down a couple of minutes, if at all. Because a lot of the comfort update process is actually checks and backing up things. The actual update usually is a couple of seconds in my experience.

But LS 6.x has a maintenance mode built in. Go to "Configuration" - "Settings" - "Global" - "General" - "Maintenance mode"

The server environment is being updated, so it might be a few hours.

I am aware of the maintenance mode, but I am unable to find an option to add a specific message to the users.

If the server itself is updated and is down for a couple of hours, how do you expect Limesurvey, that runs on this server, to provide ANY message? Not seeing how this will work.

The message should be as a warning message before the downtime. That procedure would be helpful since our freelancers usually login in advance to create the survey and will be informed about the situation.

Seems like Limesurvey doesn't offer custom messages in the maintenance mode (never use the mode, because updates are so quick that it doesn't have much impact and if the server is down nothing can be displayed anyway so I have little experience with this feature).

But if these are freelancers you most probably have their contacts. So I think it would be a good idea to send them an email informing them about the situation.

Currently I don't see any option for what you are trying to do, at least not out of the box.