Some of the technical issues with Boxee Box could have been fixed if the dev team was paying more attention to addressing the bugs rather than adding “features” of dubious value. In the final analysis, for the price and ease of use, Boxee Box is the best in its class and price range. You just need to be mindful of its limitations and buy it in hope of future improvements to its usability.
Read the full story »Unix and Linux network configuration. Multiple network interfaces. Bridged NICs. High-availability network configurations.
Reviews of latest Unix and Linux software. Helpful tips for application support admins. Automating application support.
Disk partitioning, filesystems, directories, and files. Volume management, logical volumes, HA filesystems. Backups and disaster recovery.
Distributed server monitoring. Server performance and capacity planning. Monitoring applications, network status and user activity.
Cool Unix shell commands and options. Command-line tools and application. Things every Unix sysadmin needs to know.
Most log files located in /var/log are part of the log rotation and will be compressed automatically. However, in many cases various user applications maintain log files outside of /var/log. These logs are not managed …
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Imagine a hypothetical scenario: you support hundreds of remote servers and you need to check which server you can access via SSH and which servers are not letting you log in. Doing this manually is a tedious process that many sysadmins choose to skip. The inevitable outcome is inability to quickly access a system when it really counts.
Carrier IQ is software installed on your iPhone by Apple at the request of the service providers. This system utility collect detailed usage and location data on your phone and sends it to the service providers. Supposedly, this was done to improve quality of service. In reality, however, if any such improvement actually occurred, it was only a side-effect.
Sometimes you don’t want people to reach you on your phone, but you don’t want to do something obvious, like turning the phone off. Because then they’ll just leave you a message and you will still be expected to call back. Below is a list of phone number in various US area codes that you can use to forward your unwanted calls.
Sometimes you just need something very simple to monitor a server or an application on a temporary basis. A basic ping monitor is fine, but it will only tell you if a server is responding on the network. It will not tell you if there is some other problem on the system. The script below relies on passwordless SSH setup to periodically log into the monitored nodes and check on their health by executing a local or remote script.
The Unix “man” pages are an indispensable tool even for the most experienced of sysadmins. Unfortunately, in a terminal window the text may be hard to read and getting a hard copy to take with you down to the datacenter will really test your Unix skills. The following quick script will convert the “man” page of your choice into formatted text and open it in the Web browser.
Recently I ran into a situation where I needed to reboot several HPC cluster compute nodes. A couple of systems were still running user jobs that I did not want to interrupt. I also didn’t want to sit around and watch those jobs, as there was not way of telling how long they could take to complete. The solution was to write a short script that looks something like this…
A common real-life scenario: on a multi-CPU system Oracle processed have taken over and the system has ground to a crawl. The average system load is in double-digits and even logging in takes several minutes. The possible root causes for the problem can range from inefficient SQL queries (the common problem) to insufficient system resources. But at this point you just need to make the system a bit more responsive, so you can start troubleshooting.
Changing hostname and IP is frequently required when a server is being moved from testing or development to production. The process is a fairly simple one, but steps must be performed in a certain order to avoid complications.
We have discussed using expect with sudo in an SSH session. Another common way to run commands on remote servers as root is to use the su – root command, where sudo is not configured. The trick to automating su operations using expect is to launch the su command with the spawn ssh command.
This is a simple one, but people are always asking: how do I type in Russian, Swedish, Spanish, whatever on my iPhone? Go to Settings -> General -> International -> Keyboards -> Add New Keyboard -> select your language -> select Hardware Keyboard Layout (if applicable).
In this example we will show you how to calculate simple moving average using Excel and a shell script. As more data is added to the file, the shell script and the Excel formula will automatically use the specified number of the latest data points to calculate the moving average.
Passwordless SSH works by pre-sharing public encryption keys. It is important to understand that setting up passwordless SSH opens your servers to certain security risks. A compromised user account on one server may allow the attacker to gain access to multiple systems on the network. Try to avoid using passwordless access for accounts with elevated privileges.
Let’s imagine a hypothetical scenario: you have a list of a hundred Linux servers and you need to log into each one of them and remove a local user “roger” and his home directory. Doing this by hand will get tedious and, chances are, you will make a few typos and there will be some collateral damage.
After enjoying taking apart Microsoft’s “cloud” Office 365 for the numerous shortcomings of its installation process, having to do the same for my favorite Linux distro – openSUSE – is rather upsetting. OpenSUSE installation routine went from nearly-flawless in 11.1 to mildly annoying in 11.3, arriving to moderately obnoxious in 11.4. What happened? Same as with Microsoft, poor installation workflow is to blame. One can always feel when desktop support people take over workflow tasks from server admins.
The idea here is simple: you need to connect to hosts 1..100 and execute a command in the background. The trick is to make sure the command continues to run after the SSH session terminates. Simply adding the “&” at the end of the command is not the answer here.
The CompTIA Linux+ is a certification program designed for people who’ve heard of Linux but can’t yet figure out what it is. Still, one would imagine that people running CompTIA’s Web site should be able to answer at least some of the sample exam questions posted on their site. At the end of the practice exam there is a link that says “Click here for the answers”. But if you click on that link, you will find none…
Just a quick alert: the latest version (v. 3.0.3.3) of the popular Shadowbox JS plugin for WordPress has a serious bug that exposes your WordPress installation to a major security risk. Incorrectly coded handling of the “player” tag causes all of your NexGEN Gallery images to be displayed on any page that also has single images embedded via WordPress “Add an Image” function.
Staring with version 3.1.3, WordPress introduced X-FRAME-OPTIONS support for the admin and login pages. This is a simple defensive measure against sneaky characters trying to encapsulate your blog within their own Web sites using iframes. So this new security was a welcome addition to WP for most users. I was not one of those users.
Recently I’ve ran into an unusual problem with SSH on SLES 11 SP1. The system – a small HPC cluster – is configured to use NIS for authentication and automounter maps. Whenever a user logs in, the home directory is automounted from an external NAS. Each user has a ~/.ssh directory with the authorized_keys2 and known_hosts required for password-less SSH access among the cluster nodes.
The following is a brief troubleshooting guide for an InfiniBand network found in common HPC Linux clusters. Running these commands requires OFED 1.5.2 or later package installed on your systems. Additionally, the “pdsh” (parallel shell) command is part of the HP CMU cluster management software (version 4.2.1 used in our example) installed on the head node.
The “stress” is a simple-to-use load generator for POSIX systems that I found very useful for stress-testing HPC clusters. The current version of the application is 1.0.4 and it was easy to compile and install. Stress can create configurable system load for CPU, memory, I/O, and disks. In the example below we ran “stress” on a SLES 11 HPC cluster with HP CMU 4.2 installed.
This is a quick follow-up to my earlier post about installing Ganglia from source on SLES. Here we will install Ganglia from precompiled RPMs on an RHEL server. The basic cluster setup for this example remains the same: two clusters: CLUSTER1 and CLUSTER2 with head nodes head_node1 and head_node2
Some of today’s cell phones feature camera resolution that rivals digital SLRs from two year ago. An 8-megapixel cell phone camera is no longer a novelty. Unfortunately, high resolution is the only good thing cell phone cameras have to offer and it does not translate into better pictures. If you compare photos taken with the most advanced cell phone camera to those taken with a $200 point-and-shoot digital camera, the cell phone invariably loses.
Imagine this: you created the /etc/ntp.conf file, enabled and started the ntpd service, and… the system time is still off. Is there a way to force time sync with the NTP server? It must be your lucky day. All you have to do is to connect to your box as root and run the following command…
I had to power-cycle my Windows 7 64-bit laptop. The bootup sequence looked normal and reached a point where I could see the black screen with the mouse cursor. After this stage my desktop would usually appears, but not this time. I could move the mouse and I could even establish a remote desktop connection to my laptop. But I could not log in. Every time it would reach the same point – the black screen with the mouse cursor – and it would stop.
Ever wanted to build a kick-ass home theater computer? Here we have some highly detailed instructions for putting together just such a device. It is not a DVR like TiVo or your Verizon HDTV box. …
I am sure this will sound familiar: you are copying a large amount of data – either locally or over the network – and you are wondering how long it will take and if there is a way to make things go faster.You may be surprised, but it does matter what type of files you are copying: 1Gb-worth of many small files will take considerably longer to copy than two 500Mb files. The hardware you are using is an important consideration, but it’s not the only factor limiting data transfer speed.
Most of the servers I work with are already behind an enterprise firewall, so I rarely get to configure a software firewall. In the following example, I installed Webmin and Usermin on a SLES 11 server that had SuSE firewall enabled. Webmin and Usermin by default use ports 10000 and 20000, respectively. These ports are not in the list of common services you would find in the SuSE firewall configuration GUI. There are a couple of ways of adding custom ports to the list of the allowed services.
I try my best to stay away from Windows. I wish my clients did the same. The usual difficulty of troubleshooting elusive network performance problems is amplified many-fold when there is a Windows computer at the end of the line. With Unix it’s relatively simple: run tests “a”, “b”, “c”, etc and follow the familiar process of elimination. With Windows in the picture the number of steps uses up all of the English alphabet and spills over well into the Russian one. And when you finally reach step “я”, you have to pull out your Chinese dictionary.
Here is a quick example showing how to count users logged in on a particular date using the “last” command on Linux.
By default, WordPress will not allow you to upload a file larger than 2Mb. This limit is not set by WordPress itself, but by detaul PHP configuration. This configuration file is usually /etc/php.ini, but normally …
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