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Ubuntu sudo: add-apt-repository: command not found error and solution

I‘m trying to run a command ‘sudo add-apt-repository ppa:foo/bar‘ but getting the following error:

     sudo: add-apt-repository: command not found

How do I fix this problem on Ubuntu Linux 14.04 LTS server?
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Linux Check Disk Space Command

I recently switched from a Windows server to a Linux server operating system. I am using Ubuntu LTS server. How do I find out disk space utilization information using command line option?
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How To Patch and Protect Linux Kernel Zero Day Vulnerability CVE-2016-0728 [ 19/Jan/2016 ]

A very serious security problem has been found in the Linux kernel. A 0-day local privilege escalation vulnerability has existed since 2012. This bug affects millions of Android or Linux applications to escalate privileges. Any server or desktop (32 or 64 bit) with Linux Kernel version 3.8+ is vulnerable. How do I fix this problem?
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How to use curl command with proxy username and password on Linux or Unix

My sysadmin provided me the following proxy details:
       IP: 202.54.1.1
       Port: 3128
       Username: foo
       Password: bar

The settings worked perfectly with Google Chrome and Firefox browser. How do I use it with the curl command? How do I tell the curl command to use my proxy settings from Google Chrome browser?
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The OpenSSH project released an ssh client bug info that can leak private keys to malicious servers. A man-in-the-middle kind of attack identified and fixed in OpenSSH are dubbed CVE-2016-0777 and CVE-2016-0778. How do I fix OpenSSH’s client vulnerability on a Linux or Unix-like operating system?
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How to find out when Debian or Ubuntu package installed or updated

How do I find and list installed Debian or Ubuntu Linux packages date? How can I see when packages got updated on my systems?
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How to undefine and unset a bash environment variable on Linux or Unix

I have set the shell variable. I no longer need the variable. How do I undefine or unset a variable in bash on a Linux or Unix-like desktop system?
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How to list all iptables rules with line numbers on Linux

I recently added NAT rules on my RHEL 6.x system. How do I see the rules including line numbers that I just added in Linux?
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How to check boot path (partition) in Linux

How do I identify the boot device or boot path in Linux operating system?
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How to delete a single command from history on a Linux, OS X and Unix Bash shell

I‘m working in Ubuntu bash terminal application and remotely on a RHEL server in cloud platform. I typed the wrong and dangerous command. I no longer wish to remember dangerous command in the history file. How can I remove or delete a single command from bash history file?
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