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Updated: 4 December, 2016
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Getting Started
1. Introduction
2. Switching to GNU/Linux
3. Getting openSUSE
4. Installation
The Fundamentals
5. KDE Workspace
6. Apps for Common Tasks
7. Security and Root
8. Terminal
9. Admin. Settings (YaST)
10. Installing Software
11. Software Repositories
Setup
12. MS Windows Interop
13. Multimedia Codecs
14. Browser Plugins
15. Graphics Drivers
16. Wifi
Appendix
A: Help and Docs
B: Games
C. Under the Hood
D. History and Background
E: Getting Involved
GNU Free Documentation License
Appendix C: Under the Hood
The purpose of this chapter is to give the reader a quick look and basic idea of what's going on beneath the surface of the openSUSE GNU/Linux operating system.

C.1 Main System Components
Any modern computer operating system is a very large and complicated contraption - and GNU/Linux distributions are no exception. The Linux kernel is just one of many components. The figure below shows the core components and what their respective roles are.

distro

This figure shows the main components of a GNU/Linux operating system.
C.2 File Tree
Most users will hardly ever need to work outside their home folder, but nevertheless it's probably a good idea to have a basic idea about the how the file hierarchy works.

On GNU/Linux you only have one file tree, unlike e.g. Microsoft Windows which has a different file tree for each filesystem/partition - on GNU/Linux separate filesystems/partitions are mounted in folders within a single file tree. The root folder for the file tree is "/" and paths are written using forward slashes.

So a path might look like this in GNU/Linux:
/home/username/Desktop/

In MS Windows a comparable path might look like this:
C:\Documents and Settings\username\Desktop

tip In GNU/Linux filenames and folders are case sensitive.

The root folder ("/") contains these folders by default:

/bin/ Essential tools and other programs (or binaries)
/boot/ The kernel itself, bootloader configuration, etc.
/dev/ Device files representing the various hardware
/etc/ System configuration files
/home/ Home folders of the regular users
/lib/ System library files
/media/ Legacy mount point for removable media
/mnt/ Intended for temporary mount points
/opt/ Add-on application files
/proc/ Files that give information about current system processes
/root/ The superuser's home directory
/sbin/ Essential system administrator tools, or system binaries
/selinux/ Only relevant if you're using SELinux, which you probably won't be
/srv/ Data for servers ran on the system
/sys/ Virtual file system
/tmp/ Temporary files
/usr/ Short for UNIX System Resources, e.g. all applications are installed here
/var/ Variable data

Normal users only have write permission in their /home/ folder, and rarely have any need to work outside of that.

C.3 Permissions
Coming soon...

C.4 Mounting and Removable Media
As briefly mentioned above filesystems/partitions are mounted in folders within a single file tree, this means that e.g. "/" can be on one partition or physical disk and /var/ can be on a different one, while /home/username/data/ might physically be on a third one - but they all appear in the same single file tree when navigating the file hierarchy.

You can assign mount points to internal partitions/filesystems to have them mounted durning boot using YaST Partitioner or by manually editing the configuration file /etc/fstab.

When removable media such as CDs or USB keys are plugged in a notification will appear, and the devices will appear in the left panel of the Dolphin file manager. The media will be mounted in /var/run/media/.

C.5 Hidden Files
Files and folders starting with '.' (dot) are hidden. You can make them visible in Dolphin file manager via the keyboard shortcut Alt+. or View -> Show Hidden Files in the menubar.

Applications store the user settings and data in hidden folders in the users home folder, e.g. /home/username/.mozilla/, /home/username/.config/vlc/, /home/username/.kde4/share/config/ etc. If you uninstall an application the settings and data will remain in the home folder. To "reset" an application, you just rename or (re)move the settings and/or data hidden in your home folder.

C.6 Important Config Files
In GNU/Linux configurations and settings are usually stored in human-readable plain text files. Almost any configuration can be done graphically via YaST or various other GUI applications, but nevertheless it can be useful to know the location of some key config files.

System wide configurations are mainly stored in /etc/, user settings are stored in hidden files in the home folder for the individual user.

/etc/fstab The file system table, file systems/partitions mounted during boot.
/etc/sysconfig/yast2 Configuration for YaST.
/etc/zypp/zypp.conf Configuration for the software management.
/etc/samba/smb.conf Samba configuration ("Windows Network")
/etc/HOSTNAME The hostname for the machine.
/etc/X11/xorg.conf.d/ X-server configuration files. By default autodetection is used, edit these files if you must configure the X-server.
/etc/sysconfig/kernel The kernel. For example loading extra modules during boot.
/etc/modprobe.d/50-blacklist.conf Blacklisting kernel modules.

C.7 Logs
In case of problems it's good to know the location of the main log files, most are kept in /var/log/.

/var/log/Xorg.0.log Log for the X-server.
/home/username/.xsession-errors Useful for troubleshooting applications ran as normal user.
/var/log/NetworkManager The NetworkManager system (generally only used on laptops).
/var/log/boot.msg Boot log.
/var/log/messages General system log
/var/log/YaST2/ Log files for various YaST modules and components.

C.8 Troubleshooting
Here are some basic troubleshooting tips for GNU/Linux in case an application crashes or won't start at all.
tip Reinstalling the software packages almost never solves anything, because the old settings and data will remain in hidden folders in the home folder.

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