if there was a bug, the loggs would have capturerd. and cronjob is deactivated, the plugins am using are from elgg

Without anymore info about possible errors logged in the server logs it's really impossible to provide any help. What is "completely down"? You surely get some kind of error message in the browser and/or in the server logs. We need to know about them.

The only thing that comes to my mind that I haven't menitioned yet is a crashed database. Have you checked that for example with phpMyAdmin? But even then there would be an error displayed. And a crashed table wouldn't explain the site having gone down every 30 minutes if you really have no cronjobs running. Though I wonder if you're site fully works then as any Elgg version starting from Elgg 1.9 would require at least the 1 minute cronjob for notification sending to work (or are you still on Elgg 1.8 or older - you still haven't given any info about that either).

Again, 30 minutes exactly or roughly 30 minutes? If it's not always exactly 30 minutes it's rather some server issue (resource limits) that hits the server due to too much traffic on the site. Are Apache, MySQL and other server processes still running normally? You need to look into that as "site has crashed" can have reasons not directly caused by Elgg (but maybe only indirectly if your Elgg site requires more resources than the server can handle).

Check your analytics to see if the traffic coincides with poor site performance. Follow the performance recommendations. Upgrade Elgg if possible. Check MySQL for slow queries.

Lol.

Just to turn the corner on this thread a bit...

Are ad servers a way of introducing spam if you run your own? 

Is there a way to use them in Elgg that is a healthy way to add some monetization for a network?

I ask as a new person looking at this subject for a project and was thinking ads, self hosted and only carrying those directly related to the project theme, would be a positive thing. 

Willing to learn though!

@keith I understand that  "Ad serving is the technology and service that places advertisements on web sites." if  that what you are looking for then elgg is able to accommodate other ad serving software to run ads on the elgg site. Look at a plugin in I had developed and see how elgg can work with called Gutwa - Elgg Ads Management System  https://elgg.org/plugins/1609647

Had you asked the same question before? Sorry, if it wasn't you but the same question was asked recently and as far as I remember there was no response at all on the answer I had given.

What I can say to this issue:

• Which version of Elgg?
• Are you trying to upload images with the Files plugin, with Tidypics or something different?
• In case of Tidypics, are you using the latest available, recommended version of the plugin for the version of Elgg you use?
• Could it be that you are using other 3rd party plugin not recommended for the version of Elgg you use, e.g. not explicitly recommended for any Elgg 2.x version? Have you tried if the error still occurs with all other 3rd party plugins disabled except Tidypics (if you use Tidypics for the image upload at all)?
• If using Tidypics have you tried the basic uploader instead of the html5 uploader to see if the error is caused by the html5 uploader (resulting in an ajax error) or the problem might be caused by something different?
• Have you looked into the server error log if there might be some errors logged explaining the cause of the issue?

Yes - I had a similar issue.

What type of picture did you try to upload? jpg ? png?

I tried a few. jpegs from mobile phones can sometimes be quite large, up to and over 5Mb and this causes a problem. I found that I had to reduce the size of the pic to at least half Mb to be able to upload, even though it says 5Mb was the max size.

I also tested a png file of 1 Mb and it uploaded successfully without problems. No easy fix for your AJAX problem unfortunately..

@Len If small images can be uploaded but it fails for larger images the reason for the error is any of upload_max_filesize, memory_limit, or post_max_size or even all of them set too small in Elgg's .htaccess. I've tried to explain it to you already at https://elgg.org/discussion/view/2594513/adding-photos-using-tidypics#elgg-object-2596421. The maximum filesize limit of Tidypics does no override the settings in .htaccess. It just allows to set a smaller limit than set in .htaccess. Equally important are memory_limit and post_max_size. If memory_limit is too small the resizing fails (at least likely to happen when GD php extension is used as image library as this library requires a LOT of memory for image resizing - the other two options supported by Tidypics have much lower memory requirements for resizing). And post_max_size must be large enough to handle all images uploaded in one batch.

@keith: the same to you. Please set the limits in .htaccess large enough. You can check on the Tidypics settings page on the "Server Information" tab if the values you've set in .htaccess are also used by your Elgg site. Try uploading with a small single image at first. You can also use the basic uploader (disabling the html5 uploader in Tidypics settings) as this uploader might give some better error messages (unfortunately) suppressed by the html5 uploader.

If even uploading a small image fails after setting the limits large enough, also test if another 3rd party plugin might cause some conflict with Tidypics.