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Simple ways to loop in bash shell scripts, or one-liners. Note that the variable in bash is declared without a "$", and called with it, but in perl the variable is declared with and called with a "$" at the beginning of the name. The Bash "for" Loop Loop a number of times for i in {1..10}; do echo -n "$i ";done;echo Output: 1 2 3 4 5 6 7 8 9 10 For short lists, the items can be entered manually. for num in 1 2 3;do echo -n $num;done;echo Output: 1 2 3 Loop Through Items on a List for host in `cat all.txt `;do ping -c 1 $host; done See also: How to Run a Bash Command on All Items in a List and: Ping Multiple Hosts Using Bash Nmap and Fping Loop using Perl This syntax should be familiar to C programmers. In Perl. the scalar variable does not have to be declared as it would in C (int $counter). Note that the variable name starts with "$" to indicate a scalar. #!/usr/bin/perl for($counter = 1; $counter <= 10; $counter++){ print ...

Sometimes we need a RHEL5 Repository that includes software not released by Redhat. It may be that we need a newer version, or simply something that was not included in our installation, and is not part of the standard redhat repositories. Missing RPM Have you ever tried to install something with yum, only to find that the package is not available? $sudo yum -y install vlc Password: Server | 1.3 kB 00:00 Updates | 951 B 00:00 Workstation | 1.1 kB 00:00 addons | 951 B 00:00 base | 2.1 kB 00:00 extras | 2.1 kB 00:00 update | 1.9 kB 00:00 Excluding Packages in global exclude list Finished...

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...