1. Test an SSH connection. If you can still SSH into your server, you most likely just have a software issue. If your web server application (such as Apache) has crashed, a simple restart may fix the problem. If you notice it starting to crash routinely every day or every week, you may have a security exploit.

2. If you cannot SSH into your server, try to ping and traceroute the server. If you get network connections all the way up the traceroute but cannot connect to your server, that means the network is fine, but the physical server may have crashed or been shutdown. Follow the normal procedure for rebooting. If your server is remote, you can ask your web host to reboot it. Some hosts also have automatic reboot switches that you can activate remotely. If something is wrong with the network, check with your host. They may already be diligently trying to fix the problem.

3. If rebooting does not fix the problem, and you cannot access your server, your host may offer you a KVM connection so that you can troubleshoot your server’s network settings.

4. If your host cannot even get the server to start in order to use KVM, they will probably have to re-image your box. This will erase everything, and you will be thankful at this point that you have kept backups of all websites on your server.

Photo Source: stock.xchng

Many nameservers are set to a default time of 86400 seconds (24 hours). With that setting, it takes 24 hours before all of the DNS servers globally are updated, although some Internet servers will update before others. The lower the number of seconds to live updates, the more often the nameserver will access the authoritative records.

While one’s first inclination might be to lower the TTL number so that nameservers are updated almost immediately, having a setting that is too low can cause too great of a strain on the server. If you change your DNS often, you might want to make the setting lower than one day, but if you only change it once in a while, that default setting might be fine. Some system administrators will lower the setting temporarily if they know they are about to make a big change to critical network services.

Image Source: Wikimedia Commons

Codenamed “Murder,” the project involves transforming Twitter’s servers into BitTorrent distribution clients. User bandwidth is not be utilized, but rather, one seed server distributes files between thousands of other servers owned by the company. This drastically increases the speed at which code updates can be performed.

According to Twitter engineer Ryan King, the new system has already been in place for several months. It’s great to see companies utilize technology like BitTorrent in such innovative ways.

Source | Data Center Knowledge

Answer: 127.0.0.1 is the standard ip address assigned to the lookback network interface in IPv4. Because it is a standard, all server should conform to it, and you should be able to access any open ports on your own server through that address. It is also known by the hostname “localhost”, and it is actually more common for documentation to use localhost just in case a server happens to use a different ip address.

If you are running Apache on a local machine, you can use 127.0.0.1 or localhost to access it through a web browser or other method. It is also used by MySQL, CUPS, and many other services, all using their own various ports. Even if no other network devices are setup on a Linux server, the “lo” loopback device should still be present. To find out information about it, you can type “ifconfig” from the command line. It should produce output that looks something like this:

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:49476 errors:0 dropped:0 overruns:0 frame:0
TX packets:49476 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:9790315 (9.7 MB) TX bytes:9790315 (9.7 MB)

Photo Source: Flickr

The IP 192.168.1.1 is a private address designated for use on routers and other networking devices. Since there are so few IP addresses remaining, the 192.168.x.x block has been designated for private network use. Generally a router on a network will use the 192.168.1.1 address and then assign the rest of the block to other computers– 192.168.253.539, 192.168.1, and so on.

If you have a router at home, type 192.168.1.1 into your browser. It will most likely take you to a control panel for your device. In addition, there is also an IP predominately used by modems: 192.168.100.1.

Photo | Flickr

Hostname, Listening IP, Kernel version, Distribution name, Uptime, Current number of users, Load averages, Processors, Devices, Memory, Filesystems, Network usage, and Information about running processes. All of this is presented in a user-friendly graphical format that has a changeable theme.

phpSysInfo is available for Linux, BSD, Winows, OS X, and all UNIX-like operating systems. It is completely web-based and is free software, releated under the GNU GPL. You can download it from sourceforge.net free of charge.

HP’s goal is to combine its extensive range of server offerings with 3com’s networking products. By doing so, it should be able to compete much better against Cisco, a competitor of both companies that produces servers and network hardware as well.

Dave Donatelli, an executive at HP, said the following:

Companies are looking for ways to break free from the business limitations imposed by a networking paradigm that has been dominated by a single vendor. By acquiring 3Com, we are accelerating the execution of our Converged Infrastructure strategy and bringing disruptive change to the networking industry. By combining HP ProCurve offerings with 3Com’s extensive set of solutions, we will enable customers to build a next-generation network infrastructure that supports customer needs from the edge of the network to the heart of the data center.

Expect to see more switches and other networking equipment carry the HP name in the future. This deal was a surprise to many industry insiders.

Source | Data Center Knowledge
Photo | Flickr

Answer: In the context of web servers, a user agent is any network host that connects to the server. Most frequently, it is used to refer to web browsers, but it can be other things as well. Anytime a search engine spider or other robot connects to your server, it leaves a user agent identity as well.

It is important to know about user agents because they can tell you a lot about your web site’s visitors and what types of computers they are using. Typical user agent data can include: browser brand and version, operating system brand and version, platform name, machine or processor type, and language. Some browsers allow users to specify what information to send or to send none at all.

Web server statistical software records user agent data and will display it for you in charts and graphs. You can determine how many of your users use a particular browser or operating system and make business decisions based on that data. You can also see how many of your hits and visitors are actually coming from non-human user agents. Overall, it is a very useful tool to have, and all website owners, big and small, should make use of it.

Answer: Most of the logs on a Linux operating system are kept in the /var/log directory. There you will find logs for the main system, kernel, network, hardware, Apache, MySQL, and often times other third-party applications that you might happen to install.

There are several ways to view the logs. For example, if you want to view the “messages” log:

tail -f /var/log/messages
This will show you the last few lines of the log (i.e. the latest information).

less /var/log/messages
will give you a scrollable view of the log, controlled with the arrow keyes.

more -f /var/log/messages
will give you a paged view. Pressing enter or the space bar will show more of the text, which is all loaded at once.

“SAT-3 is currently the only fibre optic cable serving West Africa,” explained Ladi Okuneye, chief marketing officer of Suburban Telecom, which provides the majority of Nigeria’s bandwidth.
“So all West African countries have to use it.”

The fibre optic cable is 15,000km (9,3000miles) long, connecting eight West African countries along is route to South Africa. 70% of Nigeria’s bandwidth is routed through Benin, causing it to suffer greatly from the cut. The company responsible for the network, Suburban Telecom, is sending a ship from South Africa to investigate. According to Okuneye, it could be two weeks before the ship arrives.

Source: BBC News
Photo: Flickr