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Memory issues finally solved
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Loading ...As I posted before in ‘Mysterious problems with my VPS’, I recently got an increasingly unstable VPS system hosting a lot of my and my customers sites. After a lot of digging I initially presumed that Dovecot (the mail server) was responsible for the issues, as you can read in ‘Dovecot causing memory issues’.
Last week I did a lot of debugging on the Debian server to try and find out what was the issue. And initially it was Dovecots memory usage. After disabling this tool for a couple of days the server was still running fine. However the day after I posted the article on Dovecot the server crashed again. So I had to restart my investigation.
First off I had to had to get a better memory management tool, so I installed Htop on the server (apt-get htop). This shows the current memory usage of each running application. After installing this I enabled all services and applications again and started running stress tests. And though Dovecot was causing some peeks in memory usage it did not keep the high memory usage after the requests where done.
As it turns out for some reason Apache 2.2 was using a lot of memory during peak loads. But even more frustrating it didn’t seem to release any memory any more. Which was causing issues for services that only spawn when they are being accessed like Dovecot and Postfix, which explained why both of these services crashed when the server halted.
After tweaking the maximum amount of servers Apache is allowed to start and the maximum amount of client threads to handle the memory usage dropped dramatically. And I am very happy to report that the server has been running again for more then a week, without any glitches.
Still it doesn’t explain why all of this only happened after updating my server with the latest versions and patches. But I’m glad it’s solved for now.
Dovecot causing memory issues?
In my previous post I mentioned that I had and still am having some serious issues with the stability of the VPS I’m running all of my websites on. Though I’m still a long way away from solving the issue, I have figured out that it is very likely caused by an upgrade of Dovecot.
Why I believe that dovecot is slowely over time eating up memory, well after I disabled it the VPS continued running without any issues. I already knew Apache 2, subversion and MySQL weren’t causing it. So I only had postfix and dovecot left to test.
What is truly amazing is that the website for Dovecot indicates it is low in memory consumption, hence it has no settings to limit the amount of memory allocated for Dovecot. So I still need to figure that part out, or alternatively change to a different IMAP server.
Postfix, MySQL setup a blackhole
In previous articles I got into how to setup Postfix and Dovecot using MySQL for management. Well this time round a question rose about creating a blackhole. Which is basically a catch all e-mail address that dumps all mail coming in.
Doing this in the MySql setup created before should be relatively easy. First of modify the ‘/etc/aliasses‘ file and add ‘devnull: /dev/null‘. This will add a virtual debian user called devnull to the system. Keep in mind this alias is not yet active. To activate it run: newaliases. This will compile the file and load it into the memory.
Now open either PostfixAdmin or MySql and add an alias from ‘@domain.com’ to ‘devnull’. Which will catch all e-mail sent to domain.com and store it into the file belonging to user devnull, which in our case is the blackhole 
.
Please be carefull, as all mail sent to the domain will be dropped unless either an alias or a mailbox is defined for the domain.
Setting up a mailserver, continued
In my last article on how to setup a basic mail server in debian using postfix and dovecot, I am now continueing on how to setup some basic spam filters. The reason to split this up, well I was stupid and assumed I wouldn’t need a spam filter yet. But I forgot that I also moved one domain to my new mail server that got 200 spam messages a day.
So now to repair my mistake I am adding the following features to my already existing mail server. To find out how to setup the mail server itself read my earlier article.
- Use spamassassin to mark spam in the header
- Change the mail delivery to dovecot LDA, this is needed for step 3
- Automatically move marked e-mails to the spam folder of the user
Sounds easy right. Well it should be 
.
Debian Setting up a Postfix and Dovecot mail server
Ok over the weekend I spent some time to finally set up my personal mail server on the VPS system I have. I had been planning this for some time, and made several unsuccessful attempts. But this weekend after spending some hard time on it I finally got it working.
My setup is as follows:
- Postfix as a SMTP service
- Dovecot as the IMAPS service and authentication service
- MySQL as a storage location indicating the virtual email boxes and domains
- PostfixAdmin as a package to manage the virtual domains and boxes
