I've got this error with buildroot-2022.11 when executing make.

Ubuntu 20.04 - added this repo as described in the link

sudo apt update
sudo apt install libc6

It automatically installed 2.35 for me.

one possible solution is to add this repo if you do not already have access to the package, as mentioned in the link:

You should be able to use any of the listed mirrors by adding a line to your /etc/apt/sources.list like this:

deb http://security.ubuntu.com/ubuntu jammy-security main

then you should be able to install the missing package:

Copysudo apt update
sudo apt install libc6

ITs works for me when i avoid /target directory and now working both version of ubuntu 20.04 and 21.10. Giving thanks to @Charles Duffy and @Herohtar for their important and useful instruction,

CopyFROM ubuntu:21.10
RUN apt-get update && apt-get upgrade -y
RUN apt-get install libssl-dev

RUN apt-get install -y -q build-essential curl
RUN curl https://sh.rustup.rs -sSf | sh -s -- -y
ENV PATH="/root/.cargo/bin:${PATH}"

WORKDIR /command-agent
COPY ./src/. /command-agent/src/
COPY .env /command-agent/
COPY Cargo.toml /command-agent/
COPY Cargo.lock /command-agent/
RUN cargo build --release

EXPOSE 8080
ENTRYPOINT /command-agent/target/release/command-agent

You don't have a high enough version of libc6, that is causing the error.

From How to fix “/lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.14' not found”? – Super User:

That means the program was compiled against glibc version 2.14, and it requires that version to run, but your system has an older version installed. You'll need to either recompile the program against the version of glibc that's on your system, or install a newer version of glibc (the "libc6" package in Debian).

So, you just need to upgrade your libc6 package. All versions of Ubuntu have at least version 2.15 because it's a faily important package (reference).

To upgrade it, use these commands in a terminal:

sudo apt-get update
sudo apt-get install libc6

That means the program was compiled against glibc version 2.14, and it requires that version to run, but your system has an older version installed. You'll need to either recompile the program against the version of glibc that's on your system, or install a newer version of glibc (the "libc6" package in Debian).

Debian has glibc 2.16 in the "experimental" repository, but recompiling the program is the safer option. Glibc is the library that everything depends on, so upgrading it can have far-reaching implications. Although there's probably nothing wrong with Debian's glibc 2.16 package, the fact that it's in the experimental repository means it hasn't received as much testing.