Linux/Unix

SASLAUTHD crashing randomly

Posted on by Andy

Sometimes saslauthd crashes randomly without leaving a trace in the logs. The downside of this is that users can't send emails then and any other service using the daemon for authentication will not authenticate. This was on our CentOS 5 x64 box.

saslauthd uses 5 threads as a default option and gives you the ability to start it with a different number of threads. We changed that number some time ago and until now there haven't been any crashes. Here what the manpage says:

-n threads
Use threads processes for responding to authentication queries. (default: 5) A value of zero will indicate that saslauthd should fork an individual process for each connection. This can solve leaks that occur in some deployments.

Now, how do we change that number? Here on a CentOS box:

* open /etc/sysconfig/saslauthd with your editor (e.g. vim, nano etc)
* change the line FLAGS="" to FLAGS="-n 0" and save the file
* now restart the saslauthd service

That resolved our crashes.

Ensim MySQL connection problems in high security mode

Posted on by Andy

Hello, if you use a site with high security settings, the site's services are chrooted to the virtual file system. Usually the mysql socket file is hardlinked inside the virtual site but in my case this stopped working once and the socket is not linked correctly, resulting in the website not finding the database server.

Now there are several workarounds for that:

  1. Do NOT use localhost to connect but use localhost.localdomain or 127.0.0.1
  2. edit your /etc/init.d/mysqld script and add following line(s) just before the "return $ret" line in the start() section:

    for dir in `ls -d /home/virtual/site*`;
    do rm -f $dir/fst/var/lib/mysql/mysql.sock;
    ln $socketfile $dir/fst/var/lib/mysql/mysql.sock 2> /dev/null;
done

Apache + mod_deflate

Posted on by Andy

With mod_deflate you can use on-the-fly compression for your content delivered by apache. The content is compressed before it is sent to the browser which decompresses then the received data. Almost all modern browsers support gzip decompression. Although the apache module is called mod_deflate it uses the gzip compression method.

I could reduce the size of a lot of pages by almost 30-40% when delivering. As you can imagine this saves quite some bandwidth and gives you the ability to serve more pages.

So, how to implement this?

first you have to enable mod_deflate in your httpd.conf. Usually this module is already loaded if not uncomment the line or add 

LoadModule deflate_module modules/mod_deflate.so

then create a new .conf file in your httpd config directory (usually something like /etc/httpd/conf.d) and add this 

# add if module is enabled
<IfModule mod_deflate.c>

    # add content compression for given mime types
    AddOutputFilterByType DEFLATE text/plain
    AddOutputFilterByType DEFLATE text/html
    AddOutputFilterByType DEFLATE text/xml
    AddOutputFilterByType DEFLATE text/css
    AddOutputFilterByType DEFLATE application/xml
    AddOutputFilterByType DEFLATE application/xhtml+xml
    AddOutputFilterByType DEFLATE application/rss+xml
    AddOutputFilterByType DEFLATE application/javascript
    AddOutputFilterByType DEFLATE application/x-javascript

    # set default compression level (1-9, higher number = higher compression)
    DeflateCompressionLevel 9

    # make some exceptions for problematic browsers
    BrowserMatch ^Mozilla/4 gzip-only-text/html
    BrowserMatch ^Mozilla/4\.0[678] no-gzip
    BrowserMatch \bMSIE !no-gzip !gzip-only-text/html

    # set the deflate logging notice
    DeflateFilterNote Input instream
    DeflateFilterNote Output outstream
    DeflateFilterNote Ratio ratio

    # and set the logging format
    LogFormat '"%r" %{outstream}n/%{instream}n (%{ratio}n%%)' deflate

</IfModule>

into a new file, e.g. deflate.conf, save it and restart your apache server. From now on every page loaded will be served with gzip compression.

You can also use gzip compression from .htaccess. Simply add this: 

# add if module is enabled
<IfModule mod_deflate.c>

    # add content compression for given mime types
    AddOutputFilterByType DEFLATE text/plain
    AddOutputFilterByType DEFLATE text/html
    AddOutputFilterByType DEFLATE text/xml
    AddOutputFilterByType DEFLATE text/css
    AddOutputFilterByType DEFLATE application/xml
    AddOutputFilterByType DEFLATE application/xhtml+xml
    AddOutputFilterByType DEFLATE application/rss+xml
    AddOutputFilterByType DEFLATE application/javascript
    AddOutputFilterByType DEFLATE application/x-javascript

    # make some exceptions for problematic browsers
    BrowserMatch ^Mozilla/4 gzip-only-text/html
    BrowserMatch ^Mozilla/4\.0[678] no-gzip
    BrowserMatch \bMSIE !no-gzip !gzip-only-text/html

</IfModule>