Archive for August, 2011

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

Performance Improved in cPanel 11.25 DNS Clustering

cPanel DNS clustering utility, DNSAdmin, now sends updates in batches with a single call, reducing the server’s memory consumption during DNS synchronization.

cPanel have also added a feature that will automatically disable unresponsive cluster members, preventing outdated information from being sent to up-to-date servers when the unresponsive server come back online. Plus, cPanel simplified reconfiguring and restarting BIND into a single call, speeding up the process.

sar - Collect, report, or save system activity information.

To have sar read a particular data file, use the -f /var/log/sa/saDD option. You can select multiple files by using multiple -f options. Since many of sar’s reports are lengthy, you may want to pipe the output to a file.

To create a basic report showing CPU usage and I/O wait time percentage, use sar with no flags. It produces a report similar to this:

01:10:00 PM CPU %user %nice %system %iowait %idle
01:20:00 PM all 7.78 0.00 3.34 20.94 67.94
01:30:00 PM all 0.75 0.00 0.46 1.71 97.08
01:40:00 PM all 0.65 0.00 0.48 1.63 97.23
01:50:00 PM all 0.96 0.00 0.74 2.10 96.19
02:00:00 PM all 0.58 0.00 0.54 1.87 97.01
02:10:00 PM all 0.80 0.00 0.60 1.27 97.33
02:20:01 PM all 0.52 0.00 0.37 1.17 97.94
02:30:00 PM all 0.49 0.00 0.27 1.18 98.06
Average: all 1.85 0.00 0.44 2.56 95.14

“The %user and %system columns simply specify the amount of time the CPU spends in user and system mode. The %iowait and %idle columns are of interest to us when doing performance analysis. The %iowait column specifies the amount of time the CPU spends waiting for I/O requests to complete. The %idle column tells us how much useful work the CPU is doing. A %idle time near zero indicates a CPU bottleneck, while a high %iowait value indicates unsatisfactory disk performance.”


VirtFS and Jailshell

VirtFS and Jailshell

When terminating an account, the VirtFS mounts for the account are removed.

The VirtFS mounts for an account are cleared when changing the shell of the account. This only happens automatically when using the Manage Shell Access interface in WHM.

Session Disruption

If a user has an active jailshell session when the Administrator changes the user’s shell, the user’s connection is terminated. This is necessary to allow successful removal of the bind mounts used in the jailshell environment.

HTTP Error 502 Bad Gateway, 503 Service Unavailable

This error is usually due to improperly configured proxy servers. However, the problem may also arise when there is poor IP communication amongst back-end computers, when the client’s ISP is overloaded, or when a firewall is functioning improperly.

The first step in resolving the issue is to clear the client’s cache. This action should result in the a different proxy being used to resolve the web server’s content.

503 Service Unavailable

This error occurs when the server is unable to handle requests due to a temporary overload or due to the server being temporarily closed for maintenance. The error signifies that the server will only temporarily be down. It is possible to receive other errors in place of 503.

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