Make sure your Linux servers' date and time are correct and synchronized

Nowadays, most people assume that all modern computers and operating systems have network time synchronization set up properly and switched on by default. However, this is not the case with many Linux servers—especially if you didn't install Linux and configure it yourself (as would be the case with most cloud-based OS images like those used to generate new servers on Linode).

After setting up a new server on Linode or some other Linux VPS or dedicated server provider, you should always do the following to make sure the server's timezone and date and time synchronization are configured and working correctly:

Drupal 6.x and PHP 5.3.x - Date Timezone warnings

This morning, I was presented with quite the conundrum: one of my servers suddently started having about 4x the normal MySQL traffic it would have in a morning, and I had no indication as to why this was happening; traffic to the sites on the server was steady (no spikes), and I couldn't find any problems with any of the sites.

munin mysql traffic spike

However, after inspecting the Apache (httpd) error logs for the Drupal 6 sites, I found a ton of PHP warnings on almost all the sites. Something like the following:

PHP: Calculating Monthly/Yearly Billing Dates - Same day next month

On a recent project, I needed to generate the timestamp for the 'same day, next month' for billing purposes. This can be tough in some circumstances, like when a user signs up on the 31st of August. What happens in September, when there are 30 days? If I were to simply try something like strtotime('+1 month'), I would get back the first day of October rather than September 30th. Same problem happens when someone hits February (oh my! only 28 days there... sometimes 29).

After looking through a bunch of different forums, Stack Overflow, etc., and finding that most people simply pro-rated the current month and billed people on the 1st (which is a valid option), I decided to write my own function that calculates the same day, next month, and simply gives the last day of the next month if the next month doesn't have as many days as this month.

It's pretty much self-documenting. It could probably be reworked to be a little faster, but I had to do this pretty quickly, and it's pretty robust imo: