File Access Bug in LAMP Virtual Machine

Using a VM as a web development test server is a great way to optimize workstation resources. My test VM is an Ubuntu installation with a standard Apache/MySQL/PHP stack. I use VirtualBox shared folders to grant the VM access to my development directory.

For some time I have been wrestling with an irritating bug that crops up when using shared folders with Apache: when a new file is created, and sometimes when existing files are modified, Apache fails to recognize the change. Any attempt to access the file via HTTP will result in a 404 error. Some searching led me to this VirtualBox bug report and the solution.

By default, Apache leverages the kernel’s sendfile mechanism to deliver resources to HTTP clients in order to optimize performance. But when a small file on a network share is altered, sometimes sendfile doesn’t bother to check its length or contents. Most of the time this is not an issue for production servers, which rarely use network storage and which don’t experience the frequent file changes of a development server. But in this case the default behavior needs to be changed.

To turn off sendfile in apache, add the following line to the Apache server configuration (i.e. /etc/apache2.conf):

EnableSendfile Off

Restart Apache to apply the new configuration.

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