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 is
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.
However, the system remains quite limited as of this writing. Many features are
missing such as proper filesystem support, bitmap graphics, and networking.
Proper filesystem support is currently being added.

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. Indeed,
I plan to construct a micro-kernel with user-space filesystems, per-process
namespaces, replacing many system calls with filesystem nodes, and other
exciting features. This design will make it safe to let normal users perform
operations such as mounting and create their own "sub-operating-system"
environment where they are the root.

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

* A 32-bit x86 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.

A number of standard utilities are present such as cat, head, tail, clear, cp,
column, kill, ls, rm, pwd, uname, echo, and uptime. There is even a number of
non-standard utilities such as calc, help, init, kernelinfo, memstat, and pager.
This collection of utilities will continue to grow as it matures and third party
software is ported. I've currently had some luck partially porting binutils,
ocaml, and gzip, but the system isn't fully ready for such software yet.

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. 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 0.7dev 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 /dev/vga and there is no framework
in place for sharing it.

Improvements in Sortix 0.6
--------------------------
The 0.6 release improves greatly upon Sortix 0.5.

* Implemented an ATA driver.
* User-space programs can now use dynamic allocation.
* Standard Error support.
* Added a new terminal driver allowing standard input from keyboard.
* Shell understands pipes, IO redirection and background processes.
* COM ports are available as /dev/comN.
* ls now formats files nicely in columns.
* Added a paging program for displaying text-files page by page.
* Support for call-traces in the kernel.
* Fixes to avoid conflicts with GRUB.
* Countless bug-fixes and small improvements.
* Massive enhancements to the standard library.

The 0.6 release drops support for the javascript virtual machine used to power
amazing things such as jslinux. This is largely because Sortix has outgrown it
and needs a less limited environment, in particular the lack of a VGA and that
the keyboard events are truncated to that of serial connections is annoying and
make it possible to keep the games compatible without severe performance
penalties.

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.

Job control and Unix signals is not fully or correctly implemented. This means
that sequences such as Ctrl-C (SIGINT) not always works correctly. This will
be implemented soon enough (depends partially on VFS; see above). Whenever you
hit Ctrl-C the kernel attempts to terminate the currently running process (even
if it isn't the foreground process). In addition, the kernel can only send
signals to running processes. This means that that programs that read a line of
input at a time from the terminal will not be terminated until you press enter.
This will be fixed when proper support for kernel threads is added.

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.
Support for quotes and escape characters is also not implemented yet. The shell
does not accept very long lines yet.

Transferring large binary streams over pipes may cause instability in the kernel
due to a bug that wasn't fixed in time for the 0.6 release. In particular, the
command $ cat /bin/cat | cat seems to trigger the issue occasionally. This bug
will likely go away when I rewrite the kernel IO framework.

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. When it does this
the init process does too, and the kernel panics. This issue is caused by the
design of the terminal system and can't be fixed until it 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.

Improvements scheduled for Sortix 0.7
-------------------------------------
* Proper kernel threads.
* Kernel virtual filesystem.
* User-space filesystem framework.
* User-space ext2 filesystem driver.
* Refactor and extend the standard library.
* Mount-points.
* Environmental variables.
* Improved terminal framework.
* New and improved shell.
* Copy-on-write in fork(2) and mmap(2).

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. If you wish to build the 32-bit
version of Sortix, you need the Netwide Assembler (nasm) as parts of it hasn't
been ported to the GNU assembler yet. 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.

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

License
-------

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

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.

The libmaxsi standard library is licensed under the GNU Lesser General Public
License, either version 3 or (at your option) any later version.

Any experimental repositories and branches on Gitorious related to Sortix but
which contains no copyright statements are also released under the GNU General
Public License, either version 3 or (at your option) any later version. These
things are so experimental that I didn't add copyright statements yet.

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.