The Sortix Operating System
===========================
Sortix is a hobby operating system. It was originally created as a tool to learn
more about kernel and operating system design and implementation. Today it is
gradually transforming into a real operating system. The standard library and
kernel is rich enough that some third party software can and has been ported to
Sortix. While the system remains limited, there have been added support for
bitmap graphics and proper filesystem support is being worked on. Unfortunately
there is no support for networking yet. The current release ships with various
test programs, utility programs and a few games and has support for rendering
the console in graphics mode.

The system aims to be an Unix-clone and is heavily based on POSIX. However, I've
drawn much inspiration from systems such as Plan 9, GNU/Hurd and MINIX. While
the system doesn't strive to be a microkernel (and today isn't), the plan is to
have user-space filesystems, per-process namespaces, subusers, and generally
give regular users more power that traditional Unix systems. If you are
interested, you can read about my design decisions at http://maxsi.org/blog/.

System Requirements
-------------------
Sortix has very low system requirements. It also works well under virtual
machines such as VirtualBox and Qemu.

* A 32-bit x86 (with SSE) or 64-bit x86_64 CPU.
* A dozen megabytes of RAM.
* A harddisk or cdrom drive or support for booting from USB.
* A multiboot compliant bootloader if booting from harddisk.
* A Parallel ATA harddisk, if you wish to access it from Sortix. SATA is not
  supported yet.

Features
--------
The current development version of Sortix offers a traditional multi-process
protected environment with round-robin scheduling. A quick and dirty shell is
able to execute programs in foreground or background mode, handle IO redirection
and piping the standard output of a process into the standard input of another.
A real shell will be added as the system matures and I get around to finish the
work-in-progress shell.

The official distribution contains a number of small utilities one would expect
on a unix system, such as cp, cat, ls, and so on. There are a lot of common
utilities missing as I haven't coded them yet. The purpose of the current
userspace is simply to test the system so don't expect too much.

Unfortunately, for technical reasons, I don't distribute ported third party
software along with Sortix. This is largely because the build system sucks but
also that statically linked libraries are big and the initrd is already big
enough as it is. However, I have successfully ported binutils, gcc, gzip, zlib,
freetype, GNU hello, and more. Once proper filesystem support is merged, I can
distribute third party software separately and it can be mounted during boot.

A number of small games is present and uses the VGA textmode to render ASCII
graphics. Notably you can play two-player Pong, or single-player Snake, or the
nice and Turing-complete Conway's Game of Life. There is also a small remake of
the asteroids game which uses 32-bit bitmap graphics. These are probably the
main attraction of the system for non-technical people.

The Sortix kernel has very basic filesystem support. The root filesystem / is
simply a single-directory RAM filesystem. The init ramdisk is mounted read-only
on /bin and various devices are accessible through the /dev filesystem. Work is
underway to create an ext2 filesystem server, but it won't be of much use until
the kernel virtual filesystem is completed in the 0.8dev development cycle.

There currently is no concept of users in the system (only the root user
exists). I decided to delay making a multi-user system until the base system is
in place. Note that there is only a single terminal - even though the system is
a multi-process system, there is only a single graphics framebuffer and there is
no framework for sharing it.

Improvements in Sortix 0.7
--------------------------
The 0.7 release improves greatly upon Sortix 0.6.

* Multithreaded and fully preemptive kernel.
* Support for Streaming SIMD Extensions (SSE) and floating point numbers.
* Support for bitmap graphics through new /dev/video/ framework.
* Environmental variables.
* Rewritten and powerful initrd format.
* Init restarts the shell if it crashes.
* BGA graphics driver.
* Console rendering in graphics mode.
* Asteroids remake.
* Improved signal handling.
* VEOF support in terminal driver and shell.
* Various shell improvements.
* Implement scanf function family.
* Support for using PAT and MTRR to speed up video memory access.
* Countless improvements to the kernel and the standard library.

In addition, a BIOS call driver was created during the 0.7 cycle as well as a
VBE graphics driver. However, the BIOS driver only worked on 32-bit CPUs and
hence wasn't merged in time. As the VBE driver depended on it, it was cut too.

Known bugs
----------
There is currently a lot of bugs and small quirks in Sortix. They are caused by
the system being young and incomplete. They will gradually be fixed as the base
system improves. They are tolerated in the releases because they are not
critical and improvement situation from the last release.

The shell only looks at whitespace when parsing input lines. This means that
operators such as & ; and | must be surrounded by whitespace on both sides.
While quotes aren't implemented, you can work around this by using backslahes
to escape all characters except newlines. The shell does not accept very long
lines yet.

Some programs change the format of the terminal standard input delivered to
them. For instance, the pong game needs to capture every keyboard event. However
running such programs at the same time as programs that need proper line-
buffered input (such as the shell) causes conflicts and neither program gets
what it needs causing programs to exit or crash. Note that if the shell fails
to read in its expected format, it exits with an error code. This issue is
caused by the design of the terminal system and can't be fixed until it is
rewritten.

The editor can only run in 80x25 terminal resolutions. This is because it is
very hacky and was written before malloc worked. This will be fixed when the
editor is rewritten.

The filesystem is currently hacked together in the kernel. When things go wrong
you may experience the utilities returning the wrong error codes. This is
harmless but confusing. All the current kernel filesystem code will be replaced
a user-space filesystem framework and will be present in the next release.

The system can partially deadlock if a process exits and zombie children are not
collected yet.

Improvements scheduled for Sortix 0.8
-------------------------------------
* New build system based on cross compilation and package management.
* Merge BIOS and VBE drivers.
* Kernel virtual filesystem.
* User-space filesystem framework.
* User-space ext2 filesystem driver.
* Refactor and extend the standard library.
* Mount-points.
* Improved terminal framework.
* New and improved shell.
* Copy-on-write in fork(2) and mmap(2).
* Pointer-safe system calls.
* And various misc. improvements.

Technical details
----------------
The system is mostly coded in C++, but also contains a few files in C. However,
the user-land experiences a normal C programming interface as per POSIX.
Executable files natively uses the ELF format used on GNU/Linux and other
systems. There is no shared library support yet, but it'll be possible when I
get around to implement copy-on-write memory, mmap(2) and swapping to disk.

Building
--------
To build the Sortix source code you need to install a few dependencies. First of
all you need the GNU Compiler Collection (C and C++), GNU Make, and GNU
Binutils. You then need to build and install the included macro preprocessor
(mxmpp) somewhere in your PATH such as /usr/bin. You need a GNU/Linux build
system to build Sortix, although, it wouldn't be difficult to port the build
system to other platforms. You can then build the Sortix kernel and user-space
utilities by running make in the Sortix root source directory. By default it
will build to your CPU architecture (64-bit on 64-bit systems, 32-bit otherwise).
Use CPU=x86 or CPU=x64 as arguments to make to control which target is built.

To build a bootable ISO you need GNU GRUB 2, as that is used by "make iso" to
generate the iso. In turn, GNU GRUB relies on xorriso to create the iso file.

You can burn the ISO to a cdrom or dvd, or even dd(1) it onto a USB memory stick
and boot from if it your BIOS supports it. You can also provide it to a virtual
machine. Alternatively you can install the kernel binary and initrd in your
/boot directory and configure GRUB to boot Sortix.

Links
-----
You can visit the official website at http://www.maxsi.org/software/sortix/ for
more information and news. You can also download the newest release and cutting
edge nightly builds from https://cs.au.dk/~sortie/sortix/release/.

You can retrieve the current git master from our gitorious project page from
https://gitorious.org/sortix/.

You can read my blog where I discuss various design decisions in Sortix at
http://maxsi.org/blog/.

License
-------
Copyright(C) Jonas 'Sortie' Termansen <sortie@maxsi.org> and contributors 2011,
2012.

Sortix is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE. See the gpl.html and lgpl.html files for more information.

See the individual files for copyright terms. If a file does not contain a
license header, you can assume it is released under the GNU General Public
Licenser, either version 3 or (at your option) any later version. This includes
Sortix-related experimental branches and repositories found on Gitorious: these
things are so experimental that I didn't add copyright statements.

Unless the license header in the source code states otherwise, the Sortix
kernel, the filesystem servers, the initrd tools, the utilities, the games, and
the benchmark programs are licensed under the GNU General Public License, either
version 3 or (at your option) any later version.

Unless the license header in the source code states otherwise, the libc library
s licensed under the GNU Lesser General Public License, either version 3 or (at
your option) any later version.