Building a statically linked binary in Alpine Linux

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#1

I did this in Docker to ensure a clean environment. Here’s what happens if I build against x86_64-unknown-linux-musl in Alpine Linux:

λ docker run -it --rm --entrypoint ash rust:1.46.0-alpine
/ # export USER=temp
/ # cargo new temp
     Created binary (application) `temp` package
/ # cd temp
/temp # rustup target add x86_64-unknown-linux-musl
info: component 'rust-std' for target 'x86_64-unknown-linux-musl' is up to date
/temp # cargo build --target x86_64-unknown-linux-musl
   Compiling temp v0.1.0 (/temp)
    Finished dev [unoptimized + debuginfo] target(s) in 0.42s
/temp # ldd target/x86_64-unknown-linux-musl/debug/temp
        /lib/ld-musl-x86_64.so.1 (0x7f1e1a2cb000)

Dynamically linked. (I also tried RUSTFLAGS="-C target-feature=+crt-static" cargo build --target x86_64-unknown-linux-musl but the result was the same.) Here’s what the same procedure results in on Debian:

λ docker run -it --rm --entrypoint bash rust:1.46.0-slim
root@806572e3c056:/# export USER=temp
root@806572e3c056:/# cargo new temp
     Created binary (application) `temp` package
root@806572e3c056:/# cd temp
root@806572e3c056:/temp# rustup target add x86_64-unknown-linux-musl
info: downloading component 'rust-std' for 'x86_64-unknown-linux-musl'
info: installing component 'rust-std' for 'x86_64-unknown-linux-musl'
info: Defaulting to 500.0 MiB unpack ram
 15.3 MiB /  15.3 MiB (100 %)   6.8 MiB/s in  2s ETA:  0s
root@806572e3c056:/temp# cargo build --target x86_64-unknown-linux-musl
   Compiling temp v0.1.0 (/temp)
    Finished dev [unoptimized + debuginfo] target(s) in 1.46s
root@806572e3c056:/temp# ldd ./target/x86_64-unknown-linux-musl/debug/temp
        statically linked

How do I build a statically linked binary inside Alpine Linux? Everything I’ve read says the musl target should be enough.

#2

Did you copy the alpine binary to another machine to test if it can be run?

Edit: You could use readelf -d <binary path> | grep NEED to check for dynamic dependencies.

#3

You’re right, readelf shows no dynamic libraries! I don’t have a Linux machine, so I copied the executable into a scratch Docker image… and it does work, this time. I must have done something incorrectly when I tried it earlier. :man_facepalming: Thank you very much for the help.