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The most popular Linux distribution, Ubuntu offers different OS versions for various devices like desktops, servers, tablets and phones. The desktop version, a fork of Debian, is very stable, particularly due to the number of active users, and provides a lot of features out of the box, so you can start working without having to install hundreds of drivers, tools and software first. For a lot of people, Ubuntu is the most competitive free OS to Windows and Mac.
SpecsUpdate
Pros
Pro Lots of support
As the most popular Linux distribution, there's a wide range of sources for support online if you ever need help, including the Ubuntu Wiki, Ubuntu Forums and the Ask Ubuntu Stack Exchange site.
Pro Use it on almost any device
Not just for laptops - Ubuntu was designed with tablets and touchscreen devices in mind, and with phone support on the way. Ubuntu also has Long Term Support releases, as well as a version oriented toward servers, so you can use the same OS at work or on mobile as you do on your desktop.
Pro Good PPA repositories available
PPA repositories allow you to install the latest version of your preferred software while keeping the rest of the operating system "stable".
Pro Just works out of the box
Lots of support for hardware, lots of pre-installed software, and a smooth install process means less time downloading drivers, less time digging through configuration files, and less time deciding on software to use just to get up and running. It also means less time digging through forums looking for support.
Pro Flexible
The setup for personal use is simple enough for anyone to achieve, and can easily be modified to act as a server. Programs and all features are easy to find and use, and first-timers can easily pick up on how to use it.
Pro Dedicated software center
The Ubuntu Software Center offers a GUI interface for installing new apps which is extremely easy and welcoming for beginners to Linux. But it should not be used by more advanced users since the method of installing through the terminal is much faster and easier after one is used to it.
Cons
Con Relatively high system requirements
The default GNOME desktop environment is a resource hog which requires hardware accelerated graphics rendering in order to run smoothly, making out of the box Ubuntu unsuitable for low end systems and older hardware. Even mildly aged hardware, you'll get far better performance out of a lighter desktop environment like LXDE or XFCE.
Con Unstable
Some people pointed out that updating Arch is a high risk affair. And one should carefully read forums before doing it. The same is true about Ubuntu. Making system updates (like it was with 10.04 to 11.04) that screw so many things up became a routine. Even LTS releases should not give confidence that it will work.
Con A tweaked Gnome version
Instead of original Gnome desktop with Ubuntu you get a tweaked Gnome and most of the tweaks makes user experience worse.
Con Redundant
With the removal of Unity, there is no point in choosing Ubuntu over Debian anymore because everything else is imported from Debian to Ubuntu.
Recommendations
Comments
Flagged Pros + Cons
Con Tracking
As of 18.04 the package ubuntu-report tracks the users' system info.
Out of Date Pros + Cons
Con Software can be outdated, if not severely outdated
If you try to download "unpopular" software, so you may find you're downloading a version that's several years old.
Con Custom PPAs required for most software (You can get most software with snaps now)
To get the most software available, user must add several PPAs to the system. That has major problems:
1) Terminal recommended for adding a PPA, which can scare away users
2) A PPA can potentially distribute malware by creating a "newer" version of a package than available in other PPAs, such as the Linux kernel.
3) PPAs must be recreated and re-added with every major system update
All of the above are valid points which Canonical would agree, that's why they went ahead and developed snap apps. You can get up to date software from snap store now, provided officially by many major vendors.
Con Canonical (author) is proprietary
Canonical is focused on making money so you can see many proprietary offers by them and the OS has built-in trackers (Amazon).
Con Includes adware (No longer the case)
Advertisers pay to have their links or software preinstalled. Like the links to Amazon installed by default in the dock. (Ubuntu doesn't have Amazon affiliate links anymore)
Con Canonical does not respect Ubuntu users' preferences in Ubuntu's standard gnome desktop environment
In 2012 it became impossible in Ubuntu to move the close-window-button back to the upper-right corner of the window, where it always was before. To the questions of their users Canonical replied that they know better than users where it would be convenient for users to have the close-window-button.
Con Problematic to integrate in Windows server environment (Active Directory)
Con Unity offers very limited customizability
The Unity desktop environment is practically non customizable with the user only being able to change certain themes and icons and adding a dock.
Con Unity interface might be confusing for new users
Unity does not align itself with the normal desktop paradigm and thus has a bit of a confusing UI in comparison to the norm of a Windows user.
Con Sends your desktop search results to Amazon, adds affiliate links, must be opted out
This is not only a huge privacy breach but also against the ethos of the free software community. It's a feature that is not meant for the benefit of the user but for Canonical instead. The feature is slated to be removed in the upcoming Unity 8 desktop release but it is, as of writing, not out yet.
Con Tends to do its own thing
Ubuntu has a user interface that is specific to Ubuntu and is now working on its own display server. It also tends to have configuration that is done slightly different (and arguably more beginner friendly) than elsewhere.
So while this is a great Linux distribution in its own right, it might not be the first choice for someone wanting to learn Linux itself.
Con Unity and other Ubuntu-specific software is problematic
Unity is awesome and user-friendly at many places. But it's not customizable at much extent. Getting rid of it can be either not possible or very problematic. Same is true about other Ubuntu-specific software. A lot of things don't work as expected. Even though the repository is based on Debian, some ways to do stuff don't actually work. It's better usually to use GUI whenever possible, than to manually edit files. This is frustrating.