Windows Azure Ubuntu - 500 OOPS: priv_sock_get_cmd error while making an FTP connection [closed]
As reto suggested, adding:
seccomp_sandbox=NO
To your vsftpd.conf file (usually located in /etc) should fix this problem (make sure you "sudo service vsftpd restart" afterwards).
VSFTPD uses kernel module seccomp in a way that produces this bug on certain kernels. See this post for more info: http://chemdroid.net/en/ubuntu/23-vsftpd-500-oops-priv-sock-get-cmd.
I wanted to add this detail to reto's post, but I don't have enough reputation to comment yet...