Answer:

Most CentOS' mirrors don't host full mirror of Yum repository for all versions of CentOS. If you are using older version of CentOS, you might one-day found the yum update is broken since the mirror no longer contains the files you needed.

In this case, you can modify the file /etc/yum.repos.d/CentOS-Base.repo and change all paths point to the following:

..
baseurl=http://vault.centos.org/...
..

Then do a yum update to reflect the changes.

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Answer:

Add a User in Linux, just use the useradd command:

# sudo useradd -d /home/john -m john

The above command will create the user john and create a home directory which is at /home/john

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Answer:

It is easy to use apt-get to install multiple softwares at the same time, without executing commands one by one.

E.g.

# sudo apt-get install curl wget lynx elinks

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Answer:

From time to time, packages will release new version so your installed packages will also need to keep updated.

To upgrade your system, first update your package index by

# sudo apt-get update

Than upgrade the packages

# sudo apt-get upgrade

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Answer:

In Ubuntu, the package index is managed by the Advanced Packaging Tool (APT).

The index of all the available packages from the repositories is defined in the file /etc/apt/sources.list file.

To update this package index, use the following command.

# sudo apt-get update

That is it.

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Answer:

The new Lucid Light themes (Radiance and Ambiance) in Ubuntu 10.04 is very nice and it can also be used in older version of Ubuntu such as Ubuntu 9.10, so you don't need to upgrade if you only want the new themes.

What you need to do is the following (for Ubuntu 9.10).

1. Add the repository
# sudo add-apt-repository ppa:nilarimogard/webupd8

2. Install all the needed files
# sudo apt-get update && sudo apt-get install gtk2-engines-murrine ubuntu-mono light-themes gtk2-engines-aurora

3. Change it in action

Reference: http://www.webupd8.org/2010/03/ubuntu-lucid-light-themes-radiance-and.html

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Answer:

To install the offical Sun (now Oracle) JDK in Ubuntu 10.04, you need to do the following in terminal.

1. Add the extra repository

# sudo add-apt-repository "deb http://archive.canonical.com/ lucid partner"

2. Update the local package index

# sudo apt-get update

3. Install the JDK and plugin

# sudo apt-get install sun-java6-jdk sun-java6-plugin

4. And finally, change you system to use the newly installed JDK.

# sudo update-java-alternatives -s java-6-sun

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Answer:

If you want to remove a package in Ubuntu, you can use apt-get remove, e.g.

# sudo apt-get remove php5

However, the config files will NOT be removed.

To remove the config files also, you can use apt-get purge, e.g.

# sudo apt-get purge php5

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Answer:

To check which Apache modules are loaded, in RHEL/Fedora/CentOS, type

# httpd -M

In Debian/Ubuntu

# sudo apache2ctl -M

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Answer:

To change MAC address, you need to take the network interface

# sudo ifconfig eth1 down

Then change it by

# sudo ifconfig eth1 hw ether 00:01:02:03:04:05

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