Diagnosing resolution problems
Traceroute is a computer network diagnostic tool for displaying the route (path) and measuring transit delays of packets across an Internet Protocol (IP) network.
Traceroute outputs the list of traversed routers in simple text format, together with timing information
Traceroute is available on most operating systems.
On Linux:
If the last line of the output does not list 8.8.8.8 as the final hop, or if there are significant timeouts, there may be a network problem preventing you from contacting our servers.
sudo traceroute -n -w 2 -q 2 -m 30 8.8.8.8
iptables/netfilter’s geoip match
Netfilter and iptables are building blocks of a framework inside the Linux 2.4.x and 2.6.x kernel. This framework enables packet filtering, network addresss [and port] translation (NA[P]T) and other packet mangling. It is the re-designed and heavily improved successor of the previous Linux 2.2.x ipchains and Linux 2.0.x ipfwadm systems. To learn more about iptables/netfilter you should visit www.netfilter.org.
This framework is modular and easily let you extend the features. This is exactly what geoip is : an extension to iptables/netfilter that allows you to filter, nat or mangle packets based on the country’s destination or provenance.
Apache MPM Common Directives
Description: A collection of directives that are implemented by more than one multi-processing module (MPM)
Description: Method that Apache uses to serialize multiple children accepting requests on network sockets
Syntax: AcceptMutex Default|method
Default: AcceptMutex Default
Context: server config
Status: MPM
Module: prefork, worker
The AcceptMutex directives sets the method that Apache uses to serialize multiple children accepting requests on network sockets. Prior to Apache 2.0, the method was selectable only at compile time.
Red Hat Enterprise Linux 5.4 Virtualization Updates
Red Hat Enterprise Linux 5.4 now includes full support for the Kernel-based Virtual Machine (KVM) hypervisor on x86_64 based architectures. KVM is integrated into the Linux kernel, providing a virtualization platform that takes advantage of the stability, features, and hardware support inherent in Red Hat Enterprise Linux.
Virtualization using the KVM hypervisor is supported on wide variety of guest operating systems, including:
Red Hat Enterprise Linux 3
Red Hat Enterprise Linux 4
Red Hat Enterprise Linux 5
Windows XP
Windows Server 2003
Windows Server 2008
Cron permissions
The following two files play an important role:
/etc/cron.allow - If this file exists, then you must be listed therein (your username must be listed) in order to be allowed to use cron jobs.
/etc/cron.deny - If the cron.allow file does not exist but the /etc/cron.deny file does exist, then you must not be listed in the /etc/cron.deny file in order to use cron jobs.
Please note that if neither of these files exists, then depending on site-dependent configuration parameters, only the super user will be allowed to use cron jobs, or all users will be able to use cron jobs.
