os is a toy Unix-like operating system for x86 computers.
Features:
- Pre-emptive multi-tasking/threading kernel.
- User and kernel process isolation; memory management.
- VT100 terminal emulator. Supports serial, text console and framebuffer graphics mode.
- Virtual file system with read/write ext2 file system.
- Minimal libc and libm implementation.
- Unix sockets.
- User space programs including sh, cat, echo, more and asm assembler.
- Capable of running various third-party programs including bash, gcc, git, python, vim, and fbdoom.
It is not robust, secure, or efficient, and should be considered highly experimental.
Live demonstration: https://pross.sdf.org/sandpit/os/
os has been tested on real x86 hardware (Intel Haswell, Intel Kaby Lake). It has also been tested with various x86 emulators including Bochs (https://bochs.sourceforge.io/), PCem (https://pcem-emulator.co.uk/), QEMU (https://www.qemu.org/), TinyEMU (https://bellard.org/tinyemu/), v86 (https://github.com/copy/v86) and VirtualBox (https://www.virtualbox.org/).
To build and boot os using QEMU, first install the prerequisites. The following command works on Debian/Ubuntu.
apt-get install -y git curl build-essential nasm texinfo libgmp-dev libmpfr-dev libmpc-dev lzip e2tools grub2-common xorriso parted qemu-system-x86 tofrodos sysvbanner
Then type make qemu. This will download and build the gcc-based toolchain, build the kernel.bin and file system, and boot into QEMU.
Once booted, os runs the init process, which then executes sh in a forever loop.
There is no user login.
See below for a list of included programs.
By default os is 32-bit.
To build a 64-bit os, edit .config and set ARCH=x86_64 etc., then perform make clean and make.
NASM >= 2.16 is required.
os can be booted many ways.
First it is important to understand the high-level design of the operating system.
os consists of a kernel file and sysroot directory. The kernel.bin file is compatible with the multiboot specification. The kernel.linux file is compatbile with the Linux boot protocol. The sysroot directory is copied to an ext2 file system, either intended to function as a ram disk (initrd) or a hard disk (disk_image).
When using multiboot with an initrd module, both kernel and initrd files must fit within the first 8 MiB of memory.
make cdrom.iso will produce bootable ISO image, where the GNU GRUB boot loader boots kernel.bin and initrd.
The ISO image can be copied to optical media or USB, and booted on real x86 hardware.
The ISO image can also be booted in QEMU using make qemu-cdrom or in Bochs using make bochs-cdrom.
When using the make qemu or make qemu-cdrom methods, initrd is copied into memory and served as a ramdisk.
Any changes to the root file system at boot time are lost on reboot.
Alternatively, initrd can be stored on a hard disk and content preserved across boots.
In this configuration, there are no partitions!
This involves setting the kernel command line string to include parameter to include root=<ROOT-DEVICE>, for example root=/dev/hda.
To boot in QEMU use make qemu-hd-initrd
make disk_image will produce a bootable hard disk image, with partition table and GNU GRUB boot loader.
At boot time, the boot loader will load kernel.bin, and then os will read files from the hard disk.
Please note that root/sudo access is required to make disk_image, because the make_disk_image.sh script uses a loopback device to mount the disk image.
To boot in QEMU use make qemu-hd. To boot in Bochs use make bochs-hd. To boot in TinyEMU use make temu-hd.
kernel.linux has been tested with GRUB, LILO, LINLD, LOADLIN and SYSLINUX.
To boot in QEMU use use make qemu-linux. To boot in TinyEMU use make temu-linux.
No operating system is complete without its own boot loader!
make boot.bin will produce a custom boot image that can be written to a hard disk or USB drive.
The image contains no files, just the boot loader, kernel and initrd stored in contiguous sectors.
To boot in QEMU use use make qemu-boot or make qemu-usb-boot.To boot into Bochs use make bochs-boot. To boot in TinyEMU use make temu-boot.
disk_image is populated from the sysroot directory.
To install third-party software, one needs to only copy files into sysroot and rebuild disk_image.
Scripts for downloading, building and installing third-party software can be found in the ports directory. For complete list of ports see ports/STATUS.md.
An example of building and running the fbdoom port is given below.
(cd ports/fbdoom && ./port)
(cd sysroot && curl --remote-name https://distro.ibiblio.org/slitaz/sources/packages/d/doom1.wad)
rm -f disk_image
make qemu-hd
Then type fbdoom -iwad doom1.wad into the os shell.
A Docker/Podman compatible configuration file is provided that builds os and boots into the serial console. To build and run, use these commands:
docker build -t os -f Dockerfile .
docker run -it os
Below is a list of features deemed experimental and disabled by default.
Kernel debug printf (kprintf) and syslog statements are littered throughout the code base.
To view these messages append -debugcon stdio to QEMUFLAGS in the Makefile then boot into os.
Pressing the PAUSE keyboard button prints a list of processes and free memory.
To attach gdb to the operating system append -S to QEMUFLAGS in the Makefile and then boot into os.
Then run gdb kernel.bin, and type target remote localhost:1234 at the gdb prompt.
os supports the NE2000 network device.
There is no Internet Protocol (IP) stack, therefore os is only capable of sending and receiving raw Ethernet frames.
To enable networking append -netdev socket,id=net0,mcast=230.0.0.1:1234 -device ne2k_pci,netdev=net0,mac=00:11:22:33:44:55 options to QEMUFLAGS in the Makefile.
For an interactive chat session between computers, boot into os, type chat /dev/net, and on the host computer type:
socat UDP-DATAGRAM:230.0.0.1:1234,bind=:1234,ip-add-membership=230.0.0.1:127.0.0.1,reuseaddr -
This is a hack that uses the complete Ethernet frame, including Ethernet frame header, to communicate data. It works because the os operates in promiscuous mode.
make qemu-pxe or make qemu-pxe-serial will boot os over PXE.
To use the text mode console, it is neccessary to first set the MULTIBOOT_VIDEO_INFO mode value to 1 (EGA text mode).
os includes the following programs. They are installed under /bin.
| Name | Description |
|---|---|
| alloc | allocate memory |
| asm | assembler |
| box | tiny version of many commands |
| cal | display calendar |
| cat | concatenate files |
| chat | real-time file descriptor chat |
| chmod | change file mode |
| cksum | compute checksum |
| clear | clear the screen |
| cmp | compare files |
| crash | deliberately cause memory access violation |
| date | print date time |
| dd | duplicate data |
| df | print mount points and usage |
| draw | draw random graphics (requires framebuffer) |
| echo | echo |
| env | print environment |
| expr | evaluate expression |
| false | return failure (1) error code |
| find | walk directory tree |
| flash | flash the screen |
| forkbomb | fork bomb |
| getty | open tty port with interactive sh |
| grep | print lines matching pattern |
| head | copy the first n-lines of input |
| hello | hello world (assembly) |
| hello++ | hello world (C++) |
| hexdump | hexadecimal dumper |
| hostname | print hostname |
| init | init process |
| kill | kill process |
| ln | create symbolic link |
| logger | write message to syslog |
| ls | list contents of directory |
| mkdir | make directory |
| more | more |
| mv | rename files |
| ps | list processes |
| pwd | print current working directory |
| reset | reset console |
| rm | remove file |
| rmdir | remove directory |
| sh | shell interpreter |
| shutdown | shutdown computer |
| sleep | sleep for duration |
| sort | sort lines of text |
| strings | print string sequences |
| tail | copy the last n-lines of input |
| tee | write standard input to standard output and file |
| testcases | execute standard library test cases |
| tolower | change text to lower case |
| touch | change file timestamp |
| tr | translate characters |
| true | return successful (0) error code |
| truncate | truncate a file |
| uname | print system information |
| unixping | ping the unixserver |
| unixserver | unix sockets demonstration server |
| vi | vi |
| wc | word count |
| xargs | run program with arguments from standard input |
There is no cp program; use cat source > dest instead.
The sh program supports running programs, pipes, redirection and background processes, but little else.
I wrote my first hobby operating system in 1998 as a learning exercise.. At this time there were very few educational resources on the Internet; many ideas were borrowed from the Linux kernel and another long forgotten website. A flat memory 32-bit x86 operating system was achieved, with minimal libc and floppy disk driver. Development was done using DJGPP and tested using Bochs and real-hardware.
In March 2022 I decided to resume the project with the goal of being able to run at least vim and gcc. A total rewrite ensured, starting with James Molloy's tutorial (http:///web.archive.org/web/www.jamesmolloy.co.uk/tutorial_html/), and progressively adding more features. It took about six weeks of spare time to create a workable system.
Peter Ross [email protected]
GPG Fingerprint: A907 E02F A6E5 0CD2 34CD 20D2 6760 79C5 AC40 DD6B