The Blue Screen of Death (BSoD) is used for the error screen displayed by Microsoft Windows, after encountering a critical system. Linux / UNIX like operating system may get a kernel panic. It is just like BSoD. The BSoD and a kernel panic generated using a Machine Check Exception (MCE). MCE is nothing but feature of AMD / Intel 64 bit systems which is used to detect an unrecoverable hardware problem.
Program such mcelog decodes machine check events (hardware errors) on x86-64 machines running a 64-bit Linux kernel. It should be run regularly as a cron job on any x86-64 Linux system. This is useful for predicting server hardware failure before actual server crash.
Unplanned downtime may be the result of a software bug, human error, equipment failure, power failure, and much more. Last week was a bad one. We faced three different downtime:
- First, there was a fiber cut for one of our data center resulting into routing anomalies due BGP reroute. Traffic was rerouted but updating those BGP tables took some time to update.
- Someone from networking team failed to follow proper maintenance procedures for network device resulted into 55 minutes downtime.
- One of our SAN hardware failure – Many internal UNIX / Linux web applications use SAN to store data including file server, tracking apps, R&D apps, IT help desk, LAN and WAN servers failed. This one lasted for 12 hrs. It was stared around midnight. The vendor replaced entire SAN hardware. Now we have dual stacked SAN as a backup device for internal usage.
Note: There is a poll embedded within this post, please visit the site to participate in this post’s poll.
The round-robin database tool aims to handle time-series data like network bandwidth, temperatures, CPU load etc. The data gets stored in round-robin database so that system storage footprint remains constant over time. Lighttpd comes with mod_rrdtool to monitor the server load and other details. This is useful for debugging and tuning lighttpd / fastcgi server performance.
Applications that perform a lot of memory accesses (several GBs) may obtain performance improvements by using large pages due to reduced Translation Lookaside Buffer (TLB) misses. HugeTLBfs is memory management feature offered in Linux kernel, which is valuable for applications that use a large virtual address space. It is especially useful for database applications such as MySQL, Oracle and others. Other server software(s) that uses the prefork or similar (e.g. Apache web server) model will also benefit.
The CPU’s Translation Lookaside Buffer (TLB) is a small cache used for storing virtual-to-physical mapping information. By using the TLB, a translation can be performed without referencing the in-memory page table entry that maps the virtual address. However, to keep translations as fast as possible, the TLB is usually small. It is not uncommon for large memory applications to exceed the mapping capacity of the TLB. Users can use the huge page support in Linux kernel by either using the mmap system call or standard SYSv shared memory system calls (shmget, shmat).
FreeBSD is just plain old good UNIX with rock solid networking stack. It is quite popular amongst hosting companies, ISPs, portals (such as Yahoo) and a few large financial institutions because of its reliability, robustness and performance.
A new version of the FreeBSD is scheduled for release next week (4-May-2009). A beta 2 was made available for download few weeks ago for final round of testing before the official launch.
This is an user contributed article.
Linux computer console is a physical device to operate a computer / server. Here are few steps which, if taken, make it more difficult for an attacker to quickly modify a system from its console.
MAC Filtering (layer 2 address filtering) refers to a security access control methodology whereby the 48-bit address assigned to each network card is used to determine access to the network. Iptables, pf, and IPFW can block a certain MAC address on a network, just like an IP. One can deny or allow from MAC address like 00:1e:2a:47:42:8d using open source firewalls. MAC address filtering is often used to secure LAN or wireless network / devices. Is this technique effective?
I’m having some weird problem with Firefox 3.0.4 under Ubuntu Linux. My test server runs inside VMWare server version 2.0. It was working fine with my Laptop. But with my desktop it started to dump errors for me. when I try to open the console of a virtual machine I have following error:
The second of two planned Release Candidates for the FreeBSD 7.2-RELEASE cycle is now available. ISO images for Tier-1 architectures are now available on most of the FreeBSD mirror sites.
The freebsd-update(8) utility supports binary upgrades of i386 and amd64
systems running earlier FreeBSD releases. Systems running 7.0-RELEASE,
7.1-RELEASE, 7.2-BETA1, or 7.2-RC1 can upgrade as follows:
# freebsd-update upgrade -r 7.2-RC2
During this process, FreeBSD Update may ask the user to help by merging
some configuration files or by confirming that the automatically performed
merging was done correctly.
# freebsd-update install
The system must be rebooted with the newly installed kernel before continuing.
# shutdown -r now
After rebooting, freebsd-update needs to be run again to install the new
userland components, and the system needs to be rebooted again:
# freebsd-update install
# shutdown -r now
Get ready for a minute with 61 seconds. Scientists are delaying the start of 2009 by the first ‘leap second’ a timing tweak meant to make up for changes in the Earth’s rotation.
The aged Earth is slowing down in its daily rotation, at least in the current epoch. So a leap second is added (a one-second adjustment added) to our time. This year will be exactly one second longer.
Precise time measurements are needed for high-speed communications systems among other modern technologies such as clusters, GPS, networks. You need to make sure that you are running updated version of ntpd that support leap second for UNIX and Windows computers.