$ cargo install xargo
    Updating registry `https://github.com/rust-lang/crates.io-index`
  Installing xargo v0.3.12
   Compiling num-traits v0.2.5
   Compiling rustc-demangle v0.1.9
   Compiling cfg-if v0.1.5
   Compiling xargo v0.3.12
   Compiling semver v0.1.20
   Compiling itoa v0.1.1
   Compiling rand v0.4.2
   Compiling same-file v0.1.3
   Compiling serde v0.8.23
error[E0463]: can't find crate for `std`
  |
  = note: the `thumbv7m-none-eabi` target may not be installed

error: aborting due to previous error

For more information about this error, try `rustc --explain E0463`.
error: Could not compile `itoa`.
warning: build failed, waiting for other jobs to finish...
error[E0463]: can't find crate for `std`
  |
  = note: the `thumbv7m-none-eabi` target may not be installed

error: aborting due to previous error

For more information about this error, try `rustc --explain E0463`.
error: Could not compile `semver`.
warning: build failed, waiting for other jobs to finish...
error[E0463]: can't find crate for `std`
  |
  = note: the `thumbv7m-none-eabi` target may not be installed

error: aborting due to previous error

For more information about this error, try `rustc --explain E0463`.
error: Could not compile `same-file`.
warning: build failed, waiting for other jobs to finish...
error[E0463]: can't find crate for `std`
  |
  = note: the `thumbv7m-none-eabi` target may not be installed

error: aborting due to previous error

For more information about this error, try `rustc --explain E0463`.
error: Could not compile `rand`.
warning: build failed, waiting for other jobs to finish...
error[E0463]: can't find crate for `std`
  |
  = note: the `thumbv7m-none-eabi` target may not be installed

error: aborting due to previous error

For more information about this error, try `rustc --explain E0463`.
error: Could not compile `serde`.
warning: build failed, waiting for other jobs to finish...
error: failed to compile `xargo v0.3.12`, intermediate artifacts can be found at `/tmp/cargo-install8AbK0H`

Caused by:
  build failed



$ rustup show
Default host: x86_64-unknown-linux-gnu

installed toolchains
--------------------

stable-x86_64-unknown-linux-gnu (default)
nightly-x86_64-unknown-linux-gnu

installed targets for active toolchain
--------------------------------------

thumbv7m-none-eabi
x86_64-unknown-linux-gnu

active toolchain
----------------

stable-x86_64-unknown-linux-gnu (default)
rustc 1.28.0 (9634041f0 2018-07-30)