Introduction to Rust

The Rust programming language is designed to be a safe, concurrent, practical language.

This package is updated on a six-weekly release cycle. Because it is such a large and slow package to build, is at the moment only required by a few packages in this book, and particularly because newer versions tend to break older mozilla packages, the BLFS editors take the view that it should only be updated when that is necessary (either to fix problems, or to allow a new version of a package to build).

As with many other programming languages, rustc (the rust compiler) needs a binary from which to bootstrap. It will download a stage0 binary and many cargo crates (these are actually .tar.gz source archives) at the start of the build, so you cannot compile it without an internet connection.

These crates will then remain in various forms (cache, directories of extracted source), in ~/.cargo for ever more. It is common for large rust packages to use multiple versions of some crates. If you purge the files before updating this package, very few crates will need to be updated by the packages in this book which use it (and they will be downloaded as required). But if you retain an older version as a fallback option and then use it (when not building in /usr), it is likely that it will then have to re-download some crates. For a full download (i.e. starting with an empty or missing ~/.cargo) downloading the external cargo files for this version only takes a minute or so on a fast network.



Although BLFS usually installs in /usr, when you later upgrade to a newer version of rust the old libraries in /usr/lib/rustlib will remain, with various hashes in their names, but will not be usable and will waste space. The editors recommend placing the files in the /opt directory. In particular, if you have reason to rebuild with a modified configuration (e.g. using the shipped LLVM after building with shared LLVM, or for the reverse situation) it is possible for the install to leave a broken cargo program. In such a situation, either remove the existing installation first, or use a different prefix such as /opt/rustc-1.47.0-build2.

If you prefer, you can of course change the prefix to /usr and omit the ldconfig and the actions to add rustc to the PATH.

The current rustbuild build-system will use all processors, although it does not scale well and often falls back to just using one core while waiting for a library to compile. However it can be mostly limited to a specified number of processors by a combination of adding the switch --jobs <N> (e.g. '--jobs 4' to limit to 4 processors) on each invocation of python3 ./ and using an environment variable CARGO_BUILD_JOBS=<N>. At the moment this is not effective when some of the rustc tests are run.

The current version of rust's num_cpus crate now recognizes that cgroups can be used to restrict which processors it is allowed to use. So if your machine lacks DRAM (typically, less than 2GB DRAM per core) that might be an alternative to taking CPUs offline. In sysv systems cgroups requires libcgroup.

At the moment Rust does not provide any guarantees of a stable ABI.



Rustc defaults to building for ALL supported architectures, using a shipped copy of LLVM. In BLFS the build is only for the X86 architecture. If you intend to develop rust crates, this build may not be good enough for your purposes.

The build times of this version when repeated on the same machine are often reasonably consistent, but as with all compilations using rustc there can be some very slow outliers.

Unusually, a DESTDIR-style method is being used to install this package. This is because running the install as root not only downloads all of the cargo files again (to /root/.cargo), it then spends a very long time recompiling. Using this method saves a lot of time, at the cost of extra disk space.

This package is known to build and work properly using an LFS-10.1 platform.

Package Information

  • Download (HTTP):

  • Download MD5 sum: a460bed79b92f6a7833ba6e6390ee6ae

  • Download size: 145 MB

  • Estimated disk space required: 7.6 GB (369 MB installed) including 294 MB of ~/.cargo files for the user building this. Add 3.3 GB if running the tests

  • Estimated build time: 39 SBU (add 31 SBU for tests, both on a 4-core machine)

Rust Dependencies


cURL-7.76.0, CMake-3.20.1, and libssh2-1.9.0



GDB-10.1 (used by the testsuite if it is present)

User Notes:

Installation of Rust

To install into the /opt directory, remove the symlink and create a new directory (i.e. with a different name if trying a modified build). As the root user:

mkdir /opt/rustc-1.47.0             &&
ln -svfin rustc-1.47.0 /opt/rustc


If multiple versions of Rust are installed in /opt, changing to another version only requires changing the /opt/rustc symbolic link and then running ldconfig.

Create a suitable config.toml file which will configure the build.

cat << EOF > config.toml
# see config.toml.example for more possible options
# See the 8.4 book for an example using shipped LLVM
# e.g. if not installing clang, or using a version before 10.0
# by default, rust will build for a myriad of architectures
targets = "X86"

# When using system llvm prefer shared libraries
link-shared = true

# omit docs to save time and space (default is to build them)
docs = false

# install cargo as well as rust
extended = true

prefix = "/opt/rustc-1.47.0"
docdir = "share/doc/rustc-1.47.0"

channel = "stable"
rpath = false

# BLFS does not install the FileCheck executable from llvm,
# so disable codegen tests
codegen-tests = false

# NB the output of llvm-config (i.e. help options) may be
# dumped to the screen when config.toml is parsed.
llvm-config = "/usr/bin/llvm-config"

# NB the output of llvm-config (i.e. help options) may be
# dumped to the screen when config.toml is parsed.
llvm-config = "/usr/bin/llvm-config"


Compile Rust by running the following commands:

export RUSTFLAGS="$RUSTFLAGS -C link-args=-lffi" &&
python3 ./ build --exclude src/tools/miri


The testsuite will generate some messages in the system log for traps on invalid opcodes, and for segmentation faults. In themselves these are nothing to worry about, just a way for the test to be terminated.

To run the tests issue python3 ./ test --verbose --no-fail-fast | tee rustc-testlog: as with the build, that will use all available CPUs.

At a minimum, two tests (run-make-fulldeps/long-linker-command-lines and run-make-fulldeps/sysroot-crates-are-unstable) may fail. If a version of gdb which was released after this version of rust is used, such as GDB-10.1, four more failures (debuginfo/, debuginfo/, debuginfo/, debuginfo/ can be expected.

As with all large testsuites, other tests might fail on some machines - if the number of additional failures is in the single digits, check the log for 'FAILED' and review lines above that, particularly the 'stderr:' lines. Any mention of SIGSEGV or signal 11 in a failing test is a cause for concern.

If you get any other failing test which reports an issue number then you should search for that issue. For example, when rustc >= 1.41.1 was built with a version of sysllvm before 10.0 the test for issue 69225 failed and that should be regarded as a critical failure (they released 1.41.1 because of it). Most other failures will not be critical.

Therefore, you should determine the number of failures.

The number of tests which failed can be found by running:

grep '^test result:' rustc-testlog | awk  '{ sum += $6 } END { print sum }'

And similarly if you care about how many tests passed use $4, for those which were ignored (i.e. skipped) use $8 (and $10 for 'measured', $12 for 'filtered out' but both are probably zero).

Still as your normal user, do a DESTDIR install:

DESTDIR=${PWD}/install python3 ./ install &&

Now, as the root user install the files from the DESTDIR:

chown -R root:root install &&
cp -a install/* /

Command Explanations

ln -svfn rustc-1.47.0 /opt/rustc: if this is not the first use of the /opt/rustc symlink, overwrite it by forcing, and use the '-n' flag to avoid getting confusing results from e.g. ls -l.

targets = "X86": this avoids building all the available linux cross-compilers (Aarch64, MIPS, PowerPC, SystemZ, etc). Unfortunately, rust insists on installing source files for these below /opt/rustc/lib/src.

extended = true: this installs Cargo alongside Rust.

channel = "stable": this ensures only stable features can be used, the default in config.toml is to use development features, which is not appropriate for a released version.

rpath = false: by default, rust can be run from where it was built, without being installed. That adds DT_RPATH entries to all of the ELF files, which produces very messy output from ldd, showing the libraries in the place they were built, even if they have been deleted from there after the install.

[target.x86_64-unknown-linux-gnu]: the syntax of config.toml requires an llvm-config entry for each target for which system-llvm is to be used. Change the target to [target.i686-unknown-linux-gnu] if you are building on 32-bit x86. This whole section may be omitted if you wish to build against the shipped llvm, or do not have clang, but the resulting build will be larger and take longer.

export RUSTFLAGS="$RUSTFLAGS -C link-args=-lffi": This adds a link to libffi to any RUSTFLAGS you may already be passing to the build. On some systems, linking fails to include libffi unless this is used. The reason why this is needed is not clear.

--exclude src/tools/miri: For a long time, the miri crate (an interpreter for the Midlevel Intermediate Representation) has failed to build on releases. It is optional, but the failure messages can persuade people that the whole build failed. However, although it is not built in the main compile, with rustc-1.35.0 it now got compiled during the install, but it was broken in that version. Omitting it should save a little time.

--verbose: this switch can sometimes provide more information about a test which fails.

--no-fail-fast: this switch ensures that the testsuite will not stop at the first error.

export LIBSSH2_SYS_USE_PKG_CONFIG=1: On some systems, cairo fails to link during the install because it cannot find libssh2. This seems to fix it, but again the reason why the problem occurs is not understood.

DESTDIR=${PWD}/install python3 ./ install: This effects a DESTDIR-style install in the source tree,creating an install directory. Note that DESTDIR installs need an absolute path, passing 'install' will not work.

chown -R root:root install: the DESTDIR install was run by a regular user, who owns the files. For security, change their owner before doing a simple copy to install them.

Configuring Rust

Configuration Information

If you installed rustc in /opt, you need to update the following configuration files so that rustc is correctly found by other packages and system processes.

As the root user, update the /etc/ file and the dynamic linker's run-time cache file:

cat >> /etc/ << EOF
# Begin rustc addition


# End rustc addition


As the root user, create the /etc/profile.d/ file:

cat > /etc/profile.d/ << "EOF"
# Begin /etc/profile.d/

pathprepend /opt/rustc/bin           PATH

# End /etc/profile.d/

Immediately after installation, update the current PATH for your current shell as a normal user:

source /etc/profile.d/


Installed Programs: cargo-clippy, cargo-fmt, cargo-miri, cargo, clippy-driver, miri, rls, rust-gdb, rust-gdbgui, rust-lldb, rustc, rustdoc, rustfmt.
Installed Libraries: Many lib*<16-byte-hash>.so libraries.
Installed Directories: ~/.cargo, /opt/rustc/lib/rustlib, /opt/rustc/share/doc/rustc-1.47.0, and /opt/rustc/share/zsh/site-functions

Short Descriptions


provides lint checks for a cargo package


formats all bin and lib files of the current crate using rustfmt


is for use by Miri to interpret bin crates and tests


is the Package Manager for Rust


provides lint checks for Rust


is an interpreter for Rust's mid-level intermediate representation (MIR). It is broken in this version


is the Rust Language Server. This can run in the background to provide IDEs, editors, and other tools with information about Rust programs


is a wrapper script for gdb, pulling in Python pretty-printing modules installed in /opt/rustc-1.47.0/lib/rustlib/etc


is a wrapper script for a graphical front end to gdb that runs in a browser


is a wrapper script for LLDB (the LLVM debugger) pulling in the Python pretty-printing modules


is the rust compiler


generates documentation from rust source code


formats rust code


is the Rust Standard Library, the foundation of portable Rust software

Last updated on 2021-02-20 16:53:06 -0600