github.com/rck/u-root@v0.0.0-20180106144920-7eb602e381bb/README.md (about) 1 u-root 2 ====== 3 4 [](https://circleci.com/gh/u-root/u-root/tree/master) [](https://goreportcard.com/report/github.com/u-root/u-root) [](https://godoc.org/github.com/u-root/u-root) [](https://github.com/u-root/u-root/blob/master/LICENSE) 5 6 # Description 7 8 u-root is a "universal root". It's a root file system with mostly Go source with the exception of 5 binaries. 9 10 u-root contains simple Go versions of many standard Linux tools, similar to 11 busybox. u-root can create an initramfs in two different modes: 12 13 * source mode: Go toolchain binaries + simple shell + Go source for tools to be 14 compiled on the fly by the shell. 15 16 When you run a command that is not built, you fall through to the command 17 that does a `go build` of the command, and then execs the command once it is 18 built. From that point on, when you run the command, you get the one in 19 tmpfs. This is fast. 20 21 * bb mode: One busybox-like binary comprised of all the Go tools you ask to 22 include. 23 24 In this mode, u-root copies and rewrites the source of the tools you asked to 25 include to be able to compile everything into one busybox-like binary. 26 27 That's the interesting part. This set of utilities is all Go, and mostly source. 28 29 # Usage 30 31 Make sure your Go version is the latest (>=1.9). Make sure your `GOPATH` is set 32 up correctly. 33 34 Download and install u-root: 35 36 ```shell 37 go get github.com/u-root/u-root 38 ``` 39 40 You can now use the u-root command to build an initramfs. Here are some 41 examples: 42 43 ```shell 44 # Build a bb-mode cpio initramfs of all the Go cmds in ./cmds/... 45 u-root -build=bb 46 47 # Generate a cpio archive named initramfs.cpio. 48 u-root -format=cpio -build=source -o initramfs.cpio 49 50 # Generate a bb-mode archive with only these given commands. 51 u-root -format=cpio -build=bb ./cmds/{ls,ip,dhclient,wget,tcz,cat} 52 ``` 53 54 `-format=cpio` and `-build=source` are the default flag values. The default 55 set of packages included is all packages in `github.com/u-root/u-root/cmds/...`. 56 57 In addition to using paths to specify Go source packages to include, you may 58 also use Go package import paths (e.g. `golang.org/x/tools/imports`) to include 59 commands. Only the `main` package and its dependencies in those source 60 directories will be included. For example: 61 62 ```shell 63 # Both are required for the elvish shell. 64 go get github.com/boltdb/bolt 65 go get github.com/elves/elvish 66 u-root -build=bb ./cmds/* github.com/elves/elvish 67 ``` 68 69 Side note: `elvish` is a nicer shell than our default shell `rush`; and also 70 written in Go. 71 72 You can build the initramfs built by u-root into the kernel via the 73 `CONFIG_INITRAMFS_SOURCE` config variable or you can load it separately via an 74 option in for example Grub or the QEMU command line or coreboot config variable. 75 76 A good way to test the initramfs generated by u-root is with qemu: 77 78 ```shell 79 qemu-system-x86_64 -kernel path/to/kernel -initrd /tmp/initramfs.linux_amd64.cpio 80 ``` 81 82 Note that you do not have to build a special kernel on your own, it is 83 sufficient to use an existing one. Usually you can find one in `/boot`. 84 85 You may also include additional files in the initramfs using the `-files` flag. 86 If you add binaries with `-files` are listed, their ldd dependencies will be 87 included as well. As example for Debian, you want to add two kernel modules for 88 testing, executing your currently booted kernel: 89 90 ```shell 91 u-root -files "$HOME/hello.ko $HOME/hello2.ko" 92 qemu-system-x86_64 -kernel /boot/vmlinuz-$(uname -r) -initrd /tmp/initramfs.linux_amd64.cpio 93 ``` 94 95 ## Getting Packages of TinyCore 96 97 Using the `tcz` command included in u-root, you can install tinycore linux 98 packages for things you want. 99 100 You can use QEMU NAT to allow you to fetch packages. Let's suppose, for 101 example, you want bash. Once u-root is running, you can do this: 102 103 ```shell 104 % tcz bash 105 ``` 106 107 The tcz command computes and fetches all dependencies. If you can't get to 108 tinycorelinux.net, or you want package fetching to be faster, you can run your 109 own server for tinycore packages. 110 111 You can do this to get a local server using the u-root srvfiles command: 112 113 ```shell 114 % srvfiles -p 80 -d path-to-local-tinycore-packages 115 ``` 116 117 Of course you have to fetch all those packages first somehow :-) 118 119 ## Build an Embeddable U-root 120 121 You can build this environment into a kernel as an initramfs, and further 122 embed that into firmware as a coreboot payload. 123 124 In the kernel and coreboot case, you need to configure ethernet. We have a 125 `dhclient` command that works for both ipv4 and ipv6. Since v6 does not yet work 126 that well for most people, a typical invocation looks like this: 127 128 ```shell 129 % dhclient -ipv4 -ipv6=false 130 ``` 131 132 Or, on newer linux kernels (> 4.x) boot with ip=dhcp in the command line, 133 assuming your kernel is configured to work that way. 134 135 # Hardware 136 137 If you want to see u-root on real hardware, this 138 [board](https://www.pcengines.ch/apu2.htm) is a good start. 139 140 # Contributions 141 142 See [CONTRIBUTING.md](CONTRIBUTING.md) 143 144 Improving existing commands (e.g., additional currently unsupported flags) is 145 very welcome. In this case it is not even required to build an initramfs, just 146 enter the `cmds/` directory and start coding. A list of commands that are on 147 the roadmap can be found [here](roadmap.md).