System Notes Org

When studying for a Cisco certification such as CCNA, CCNP, CCIP, or CCIE, there is nothing like having real routers and switches to play with, but it can get expensive to build a lab to study with. There is an excellent simulator that is free, but the users must supply their own Cisco IOS software. Once it is set up, the simulated routers, switches, and firewalls act as if they were real hardware. That gives the user flexibility to play with the real Cisco IOS from command prompts on the simulated hardware. What is GNS3? GNS3 is a graphical network simulator that allows you to design complex network topologies. You may run simulations or configure devices ranging from simple workstations to powerful Cisco routers. It is based on Dynamips, an IOS emulator which allows users to run IOS binary images from Cisco Systems and Pemu, a PIXOS emulator to emulate PIX firewalls. Where Can I Download GNS3? http://www.gns3.net How To Configure GNS3 This installation assumes you have a cisco rout...

Hard drive data recovery is one of the most difficult tasks a sysadmin can attempt to perform, so it should be considered a last resort that, after many frustrating hours, may not even work at all. Data Recovery or Disaster Recovery can be thought of in several categories, and it is important to have a plan in place, and know the options before resorting to one of your local hard disk data recovery services. Many people fail to consider the value of their data until it is too late. This article discusses general principles, with some specific examples from experience with Novel, Microsoft, and Linux operating systems. Detailed tool discussions will be reserved for separate posts. Here is a short list of categories, roughly in order of increasing level of difficulty to recover. Backups and off-site storage RAID Documents File Systems Data Recovery from Hard Drives There is software available that can recover from several types of failures, but it does not always work when ther...

I wrote some shell scripts to generate Nagios configuration files, and I finally decided to publish them on Freshmeat . The initial version is crude, and has some hard-coded information, but it is still better than trying to edit the .cfg files by hand. Here is a brief description nagios-config-build is a group of shell scripts that generate Nagios configuration files from a list of hostnames. It automatically resolves IP addresses from DNS, and provides a quick way to manage a large number of hosts without having to set up a complicated system. Nagios is more than just a server monitoring tool. From the Nagios website: " Nagios is a powerful monitoring system that enables organizations to identify and resolve IT infrastructure problems before they affect critical business processes." Systemnotes.org download: http://www.systemnotes.org/download/shell/nagios-config-build.html Freshmeat project: http://freshmeat.net/projects/nagios-config-build Please feel free to use thi...

Have you ever been in the middle of editing something in vim, and noticed "recording" on the lower left of the screen? If you were in a hurry, you probably just continued typing, and thought, maybe I'll use that feature some day, but as long as it lets me continue I won't worry about it. Well it's really quite simple to use once you know the sequence. Here is a high level overview on how to use the macro recording feature of vim. High Level Steps to Record and Play a Macro in Vim 1. Press q to Start recording, followed by a lower case character to name the macro. 2. Perform any typical editing, actions inside Vim editor, which will be recorded. 3. Stop recording by pressing q. 4. Play the recorded macro by pressing @ followed by the macro name. 5. To repeat a macro multiple times, press : n @ macro name, where n is a number. For more details, check out a complete tutorial at thegeekstuff.com: Vim Macro Tutorial: How To Record and Play

As I was writing a script, I noticed that I pressed Shift-PageUp without even thinking about it. Then I realized that there are a lot of shortcuts we take for granted as Sysadmins. I thought it would be helpful to share some of them. This is not a comprehensive list, but a few shortcuts I find myself using all the time. Bash Shell shortcuts Shift-PageUp / PageDown See more of the screen Ctrl-a, Ctrl-e Move to beginning / end of line up & down arrows See bash history !! / !$ Execute the previous command / parameter !n Execute the nth command in history Ctrl-D Logout, or exit Ctrl-u, Ctrl-h, Ctrl-b Delete previous char, or entire line Alt-F1 to Alt-F7 Switch to another console —see also: using-bash-history , ...

An alias is a built-in way of modifying the way a command works, or it is used as a shortcut for another command. For example, you may find that you often type "ls -l", or "ls -ltr", and think it would be nice if you could type less characters. You can create an alias, so that all you would have to type is "ll", instead of "ls -l." To add an alias to your .bashrc file: $ vi ~/.bashrc Insert these lines: alias ls='ls --color=tty' alias ll='ls -l' In order for the new alias to take effect, you can open a new console, login again, or simply source your .bashrc file. You also have the option of running bash again to open a new shell, or just running the alias command. What do I mean by source the file? You can either run a script, or have the shell read the variables in a script without actually running it. This is called sourcing a file, and is accomplished by typing either "source", or "." followed by th...

I mentioned previously that you can reset a shell by typing "reset." There is another problem that can cause a shell or xterm to freeze. If you ssh to a remote host, and then logout, sometimes the session will freeze. In that case, all you need to do is type "Enter", "~", "." (Enter, Tilde, Dot with no spaces) to get the console back. That's the Enter key, immediately followed by tilde "~", and then a period "." [Enter]~. Also, a convenient way to exit a shell, xterm, or remote ssh terminal is to use Ctrl-D rather than taking the time to type the word "exit."