A Linux OS simple enough to build and edit yourself.
Build for {x86, x86_64, arm, arm64, riscv64}.
Pre-built artifacts available in releases.
Build in a Podman container and then launch with QEMU:
$ ARCH=x86_64 \
SSH_KEY="$(cat ~/.ssh/*.pub)" \
./simplelinux.sh
simplelinux build
start: Thu Nov 2 04:58:19 PM PDT 2023
log: /home/simp/simplelinux/build/out/x86_64/build_log.txt
end: Thu Nov 2 05:03:12 PM PDT 2023
outputs: /home/simp/simplelinux/build/out/x86_64
1.3M build_log.txt
1.2M busybox
807K dropbearmulti
1.1M initramfs.cpio.gz
1.1M initramfs.tar.gz
13M kernel
64M simplelinux.img
simplelinux build complete
$ ARCH=x86_64 \
SSH_PORT=8181 \
./scripts/qemu.sh
====== simplelinux ======
booted in 1.64 seconds
Please press Enter to activate this console.
You can SSH in on port 8181: ssh root@localhost -p 8181.
simplelinux.sh sets up a minimal Alpine Linux container and runs
scripts/build.sh within in, which in turn runs the following:
./scripts/getdeps.sh # apk build dependencies
./scripts/getsrcs.sh # download sources
./busybox/build.sh # build busybox
./ssh/build.sh # build dropbear
./linux/build.sh # build linux
./ramfs/build.sh # build root filesystem
./boot/build.sh # build boot image
You may want to modify the files in the root filesystem, which are in
ramfs/rootfs. ramfs/build.sh is responsible for the final construction
of the initramfs archives.
$ find ramfs/rootfs -type f
ramfs/rootfs/etc/init.d/pseudofs.sh
ramfs/rootfs/etc/init.d/banner.sh
ramfs/rootfs/etc/init.d/busybox.sh
ramfs/rootfs/etc/init.d/hostname.sh
ramfs/rootfs/etc/group
ramfs/rootfs/etc/fstab
ramfs/rootfs/etc/passwd
ramfs/rootfs/etc/runit/1
ramfs/rootfs/etc/runit/2
ramfs/rootfs/etc/runit/3
ramfs/rootfs/etc/service/syslog/run
ramfs/rootfs/etc/service/dhcp/run
ramfs/rootfs/etc/service/cron/run
ramfs/rootfs/etc/service/ntp/run
ramfs/rootfs/etc/service/ssh/run
ramfs/rootfs/etc/busybox.conf
ramfs/rootfs/etc/inittab
ramfs/rootfs/etc/shadow
ramfs/rootfs/etc/ntp.conf
ramfs/rootfs/etc/hostname
ramfs/rootfs/etc/hosts
ramfs/rootfs/var/spool/cron/crontabs/root
simplelinux is configured through a few environment variables. Further
configuration should be done by editing the files.
Build:
# one of {x86, x86_64, arm, arm64, riscv64}
ARCH=x86_64
# one of the names in linux/configs/$ARCH, or default
KERNEL_CONFIG=default
# public key(s) to put into /root/.ssh/authorized_keys
SSH_KEY="$(cat ~/.ssh/*.pub)"
# if 1, mounts pwd and drops into shell
DEBUG=0
./simplelinux.sh
Boot:
# one of {x86, x86_64, arm, arm64, riscv64}
ARCH=x86_64
# one of {kernel, boot}
# kernel uses QEMU's ability to a directly boot a Linux kernel
# boot uses simplelinux.img with either BIOS or UEFI
MODE=kernel
# port forward for ssh
SSH_PORT=8181
# optionally attach a disk, typically created by qemu-img
# if not partitioned, use fdisk, and then mkfs.ext2 to create a fs
# example mount: mount /dev/vda /home
DATA_DISK=/path/to/data.img
./scripts/qemu.sh
Run initramfs in a Podman container:
# one of {x86, x86_64, arm, arm64, riscv64}
ARCH=x86_64
./scripts/podman.sh
simplelinux uses runit for its init system.
/etc/runit/1: One-time startup tasks/etc/runit/2: Long-running services/etc/runit/3: Shutdown tasks
simplelinux uses runsv for service management.
Services can be started/stopped by adding/removing a directory to
/var/service.
Use sv to query and manage services (sv status /var/service/* to see the
status for all services).
Default startup tasks:
- Install busybox symlinks
- Set hostname
- Mount pseudo-filesystems
- Startup banner
Default services:
- syslog
- cron
- dhcp
- ntp
- ssh
Default shutdown tasks:
- Stop services
- Turn off swap
- Unmount filesystems
By default, the Linux kernel is configured with its defconfig make rule.
To specify an alternative config, you can place a configuration file in
linux/configs/$ARCH/some_config_name and set KERNEL_CONFIG=some_config_name
for the simplelinux.sh build script.
The available ones in the repo for x86_64 are:
minconfig(compressed kernel <3MiB):clangmake allnoconfig+clangmake kvm_guest.config+ the following:-> General setup System V IPC Initial RAM filesystem and RAM disk (initramfs/initrd) support Only gzip compression Configure standard kernel features Deselect "Load all symbols for debugging" -> Executable file formats Kernel support for scripts starting with #! Disable core dump support -> Networking support -> Networking options Packet socket -> Device Drivers -> Generic driver options Maintain a devtmpfs filesystem Real Time Clock -> File systems -> Pseudo filesystems Tmpfs virtual memory file system support
Note: clangmake is the make wrapper generated in linux/build.sh.
minconfig boots in QEMU with KVM in ~0.25s, the kernel and initramfs weigh in
at <4MiB, and the system uses ~12MiB of memory after startup.
$ ARCH=x86_64 \
KERNEL_CONFIG=minconfig \
SSH_KEY="$(cat ~/.ssh/*.pub)" \
./simplelinux.sh
simplelinux build
start: Thu Nov 2 05:37:20 PM PDT 2023
log: /home/ryan/projects/simplelinux/build/out/x86_64/build_log.txt
end: Thu Nov 2 05:40:18 PM PDT 2023
outputs: /home/ryan/projects/simplelinux/build/out/x86_64
1.2M build_log.txt
1.2M busybox
807K dropbearmulti
1.1M initramfs.cpio.gz
1.1M initramfs.tar.gz
2.7M kernel
64M simplelinux.img
simplelinux build complete
$ ARCH=x86_64 ./scripts/qemu.sh
====== simplelinux ======
booted in 0.25 seconds
Please press Enter to activate this console.
DEBUG=1 drops you into a shell in the Podman environment. Typically
it would run ./scripts/build.sh but you can manually run commands yourself.
DEBUG=1 ./simplelinux.sh
# . scripts/config.sh
# ./scripts/getdeps.sh
# ./scripts/getsrcs.sh
- TinyCore Linux, by Robert Shingledecker
- Aboriginal Linux, by Rob Landley
- Linux from Scratch, by Gerard Beekmans
- Zig, by Andrew Kelley
- Linux, by Linus Torvalds
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