Console Tricks Seminar¶
1. Introduction: What Is a Shell?¶
Confused?
1. Introduction: What Is a Shell?¶
But is that a shell?
Yes and no. Let's have a look at the definition of a shell:
In computing, a shell is a user interface for access to an operating system's services. In general, operating system shells use either a command-line interface (CLI) or graphical user interface (GUI), depending on a computer's role and particular operation. Wikipedia
Maybe you wouldn't expect it, but the Windows Desktop, including the Windows Explorer, is a shell (and Microsoft actually calls it so).
On Linux systems we usually mean CLIs (command-line interfaces) when we're talking about shells. That doesn't mean that there aren't graphical shells. The X window system + your desktop environment is also a shell.
1. Introduction: What Is a Shell?¶
Back to our Linux “shell”…
What we see here are actually two things:
- A graphical terminal emulator
- A shell command prompt
2. Getting Started: The Basics¶
Where do I find stuff?¶
Linux systems (and many other UNIX-like systems) follow a filesystem structure standard called the “Filesystem Hierarchy Standard” (FHS).
Basic principle: All folders fall into these two orthogonal categories: shareable vs. unshareable – static vs. variable
“Shareable” files are those that can be stored on one host and used on others. “Unshareable” files are those that are not shareable. For example, the files in user home directories are shareable whereas device lock files are not.
“Static” files include binaries, libraries, documentation files and other files that do not change without system administrator intervention. “Variable” files are files that are not static.
2. Getting Started: The Basics¶
Furthermore, the standard defines a basic folder tree.
The most important directories:
/– The root filesystem/bin– Essential user command binaries/boot– Static files for the boot loader/dev– Device files/etc- Host-specific system configuration/home– User home directories/lib(/lib64) – Essential shared libraries and kernel modules/media– Mount point for removable media/mnt– Mount point for temporarily mounted filesystems/opt– Add-on application software packages/root– Home directory of the root user/run– Run-time variable data/sbin– System binaries/srv– Data for services provided by this system/tmp– Temporary files
2. Getting Started: The Basics¶
Besides these top-level directories FHS defines two secondary filesystem trees:
/usr– Contains shareable, read-only data used by all users of the system/var– Contains variable (shareable and unshareable) data files (e.g. mail spools, log files, temporary files)
Both directories contain a subtree similar to the top-level root filesystem tree.
Most notable sub-directories of /usr:¶
/usr/bin– Most user command binaries/usr/lib– Libraries and object files for user programs/usr/share– Static, architecture-independent resource files (definitions, icons, media files, *.desktop files, static game data etc.)
2. Getting Started: The Basics¶
Important configuration files¶
Besides the preceding list of directories, there are also some very important configuration files which you should know about.
/etc/passwd– usernames and home directories, readable by everyone (usually no passwords included, despite the name)/etc/shadow– passwords for users, only readable by root/etc/hosts– mapping from 127.0.0.1 and [::1] to localhost, additional hostname configurations/etc/fstab– system-wide mount points for storage devices/etc/profile,/etc/profile.d/*– global shell settings
End of Lesson 1¶
That marks the end of lesson 1. Next time we'll focus on some more advanced command line techniques. We'll cover:
- Globbing
- Environment variables
- Basic scripting
- Input/Output redirection and Piping
- Background jobs
Thanks for listening.