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operating systems

Bash Shell: Find Out If a Variable Is Set or Not

How do I check if a bash shell variable called $input is defined or not under BSD / Apple OS X / Unix / Linux like operating systems?
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OpenBSD: Install Firefox Web Browser

How do I install Mozilla Firefox which is a free and open source web browser under OpenBSD operating systems?
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ifconfig Command Does Not Show IPv4 Address

ifconfig command does not show IP address on my Linux based laptop computer. How do I fix this problem?
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Use export Command in Linux / Unix

How do I use export command under a Linux or Unix-like operating systems to set variables on a bash shell?
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Install Iptables Firewall in Redhat / CentOS Linux

How do I install iptables under Redhat (RHEL) or CentOS or Fedora Linux operating systems?
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Linux / UNIX: TZ Environment Variable

What is the correct format for a TZ (time zone) environment variable for use with the Linux or UNIX operating system?
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ping command: TTL Expired In Transit Error and Solution

When I try to ping other UNIX / Linux / BSD or MS-Windows servers in our network I get the following message:

TTL Expired In Transit

How do I fix this problem?
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KVM Virtualization: Start VNC Remote Access For Guest Operating Systems

I'm running a KVM virtual machine (FreeBSD 7 and Fedora Linux 13 desktop) under Redhat Enterprise Linux 5.5. However, I'm not getting the remote access via VNC (Virtual Network Computing) to access my Fedora Linux graphical desktop or FreeBSD console. How do I turn on VNC support without reinstalling both operating systems?
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FreeBSD: Disable / Stop Console Beep ( Bell )

I know how to turn off console beep under Gnome Linux desktop. How do I stop console beep under FreeBSD operating systems?
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UNIX: Loop Through Files In A Directory

How do I loop through files in a directory under UNIX like operating systems?
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