Busybox Rootfs Download

Your assumption that Busybox can generate a complete rootfs is simply incorrect.The purpose of Busybox is only to "combine tiny versions of many common UNIX utilities into a single small executable ... with size-optimization and limited resources in mind".

In fact the Busybox 'About' page explicitly mentions that "to create a working system, just add some device nodes in /dev, a few configuration files in /etc, and a Linux kernel". This comment seems to assume a static build that would not require any (dynamic/shared) libraries in a /lib directory.

You could use a build tool such as Buildroot (note the verb+object construct of this name) or Yocto, that could build a toolchain, boot program(s), the Linux kernel, and a variety of userspace programs and libraries to populate a complete (or minimal) rootfs.

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Note that those instruction are for a "network boot", i.e. the boot programs (MLO and U-Boot) are retrieved from local storage (eMMC), but the Linux kernel and root filesystem are network-based (the kernel is retrieved using TFTP and the rootfs uses NFS).

You neglect to clarify or specify where you expect this rootfs to reside. Note that Buildroot can be easily configured to produce a rootfs image (or archive) specifically for the intended medium.

If your board has sufficient memory and the rootfs is not too large, then a convenient form of rootfs is memory-resident, that is, an initramfs (which should not be confused with ramdisk). Buildroot is capable of easily building an initramfs; seehow to rebuild rootfs in buildroot

For several reasons I have a need for a simple/minimal system that can be used in an existing userspace or as its own userspace. Usually I would jump to tools like buildroot or openwrt for such things. I've used buildroot several times in my other articles for building cross toolchains, rootfs environments, and kernels for several use cases. Instead of going with an end-all-be-all solution like buildroot, I'd like to take a more simple approach that leans more on the tools readily available by the Ubuntu/Debian distribution.

To summarize the plan, I'd like to build a fully bootable system that will run within a QEmu emulation. For this, I'd like to build my own libc, kernel, and userspace. Other than those three components, we'll need the qemu emulator and cross compiler/toolchain. It is also worth mentioning that we're drastically simplifying this build by making busybox static. This means that we won't have a dynamic linker or shared object requirements for the resulting root filesystem.

busybox 1.32.0 - This is a one stop shop for nearly everything we need in the userspace. The largest need this tool fills is that it acts as the shell we'll use to interact with our system and userspace.

Within our build environment, we'll actually be building two different environments. The sysroot environment contains all of the files required to build files from source code against our kernel and libc. The rootfs environment will contain all the files required to run our userspace within the target system. In otherword, sysroot is required for building things, rootfs is required for running things.

After musl is built and installed, there is still a number of system specific header files that need to be included in the sysroot to build busybox. The linux headers are where headers that start with asm/ or bits/ come from. Note: You can't just point your -I arguments at the kernel directory or copy the headers from the kernel tree because as part of the headers_install target, a number of header file locations are adjusted or generated.

Finally we'll start to run through the busybox build. Start by extracting and configuring busybox. Note: There are some expected configurations that you should use below. Its also worth nothing that there are a number of features of busybox that aren't inherently supported with our minimal environment. For example, the SCSI Eject capability will not build in our environment so you may need to disable that as part of your configuration.

Note: If you've been working with busybox before attempting these instructions, you need to remove references to -nostdinc and -nostdlib because these override the settings found in the musl specfile.

Congratulations, you should now have a working busybox static binary! Although we plan to build a complete system that boots from our kernel, at this point you can test the busybox build with the userspace qemu emulator:

For the kernel to pass control to the userspace, it attempts to execute an init process as the first process. Therefore we'll create our own shell script to run as the first process. Create rootfs/init script:

The next step is take our volatile system and make it into a non-volatile system so that when we make changes from within the emulation they will stick. Just like before, we want to create a build_rootfs.sh script that we'll run with the fakeroot tool. The following script will create an ext3 disk image that is intended to max out at 32 megabytes.

In building our minimal system we built our own kernel followed by a sysroot with linux headers and the musl libc headers and executable code. Using the sysroot, we were able to build a static busybox and initialize the busybox-based rootfs. Finally, some additional scripting was created and executed to setup a minimal file system hierarchy for the kernel to initalize the system and pass control to busybox for user interaction.

When I get time to adjust this ... In hindsight, it makes more sense to build the minsys folder first and then keep all built objects there. For example, first build minsys and then make sure it contains the kernel Image, the non-volatile disk.ext3, and the volatile initramfs.cpio.gz. It will also contain the build_rootfs.sh, build_initramfs.sh, rootfs, sysroot folders and scripts. Then from this single directory we can execute our fakeroot and qemu commands without any directory traversal. We should also be able to generate all of this from a single docker build command.

I am building a Linux system from the bottom for a Beagle Bone board. I have compiled the vanilla kernel and built a basic root file system with busybox. The system is booted with U-boot, while the rootfs is located on a Linux PC and exported through NFS:

I've encountered a problem when trying to get su working for non-root users. In order to work around the problem people over internet are suggesting to set the suid bit for the busybox binary. After doing so:

If setting the flag from within the running shell on the Beagle Bone board itself, the shell is stopping responding right after the chmod is performed. I suspect it is something to do with the way the NFS is exporting the rootfs, but it's only a guess, so qualified explanation and possible solution would be helpful.

After some research I will answer my question myself. The answer is very simple. In order the above to work, the busybox binary should be owned by root:root. The simplest solution is just to change the ownership.

My customer found some of the routines in the ./bin path are not link to the busybox, for example the mount is link to umount.util-linux-ng, they tried to relink the mount to busybox and it worked. Is there any different between using busybox and util-linux-ng? Why we used util-linux-ng rather than busybox, any reasones or issues faced? Are there any risk for re-linking all the util-linux-ng to busybox? Any comments are welcome.

Louis Lu93481 said:My customer found some of the routines in the ./bin path are not link to the busybox, for example the mount is link to umount.util-linux-ng, they tried to relink the mount to busybox and it worked. Is there any different between using busybox and util-linux-ng?

[ORB] -- not sure why we are using util-linux-ng or the diff between the two. Normally I would use busybox as a minimal rootfs during borad bringup. This would allow you to test your environment prior to loading a full distro.

A few directories are required for the system to work properly. Travel to the L4T rootfs folder and observe that /bin, /sbin, and /usr have already been made from the Busybox install. Now we need to make the rest of them.

NOTE: This assumes you have been assembling your filesystem within /rootfs/, as indicated by the instructions above. If you have been doing this elsewhere, give applied_binaries a -r flag to indicate where your rootfs is.

Before we can boot our virt board, we need to prepare a disk image with a root filesystem (rootfs). The rootfs will mainly be provided by BusyBox, though we'll need to create a few additional directories for mount points, startup scripts and the like.

Next we need to remove linuxrc, we are doing this because linux looks for an executable called init when the first process starts up. We will need to link this to our busybox executable. Remember for this to work we need to be in the install directory for our root filesystem.

Almost done, the last step is to add the u-boot header that u-boot needs to load the rootfs image. We will also be changing the name since xilinx u-boot will be looking to load a file called uramdisk.image.gz

/dev/sdb1 is my ntfs partition, which gets mounted to /new_root in busybox. I tried umounting it and re-mounting it to /host, then I mounted /host/images/archlinux.img to /new_root. Is there anything I'm doing wrong? Also I think I'm probally missing directorys in my initramfs-linux.img.

But I don't know where to start. I am not sure whether to create the final image by modifying the basic recipe (imx-image-full) in the Yocto Project or by copying the required library to the busybox folder separately.

I'm stuck on the step of copying the filesystem. This question is relevant, but none of the recommendations work because I have only busybox versions of the cp and cpio tools, and the --one-file-system option is unsupported by busybox.

How can I clone the root filesystem when I only have the tool capabilities provided by busybox? Would it help to run archive creation commands on the NFS server (x64 architecture running Ubuntu) and then unpack on the target? ff782bc1db