How to fix dpkg-preconfigure: unable to re-open stdin: No such file or directory in APT

The most reliable solution is to set the environment variable before running apt commands. This tells debconf to use the noninteractive frontend, which skips all prompts and uses default answers:

FROM ubuntu:22.04

# Set noninteractive frontend
ENV DEBIAN_FRONTEND=noninteractive

# Now apt-get runs without trying to prompt
RUN apt-get update && apt-get install -y \
    curl \
    git \
    wget

# Optional: reset for subsequent stages
ENV DEBIAN_FRONTEND=dialog

The ENV instruction works for all RUN commands that follow it in the same image stage. If using multi-stage builds, set it in each stage that needs it.

Important: Use ENV (persistent) rather than ARG (build-time only). Some older Docker versions don't properly pass ARG to RUN commands.

Some debconf-related tools try to show changelogs. Disable them as well:

FROM ubuntu:22.04

ENV DEBIAN_FRONTEND=noninteractive
ENV APT_LISTCHANGES_FRONTEND=none

RUN apt-get update && apt-get install -y curl git

This prevents apt-listchanges from trying to interact during installation.

Optionally configure locale settings to avoid perl warnings and ensure consistent encoding:

FROM ubuntu:22.04

ENV DEBIAN_FRONTEND=noninteractive
ENV LANGUAGE=en_US.UTF-8 \
    LANG=en_US.UTF-8 \
    LC_ALL=en_US.UTF-8

RUN apt-get update && apt-get install -y curl git

This is optional but recommended for cleaner build logs.

For existing containers or systems that already have the error, you can disable preconfiguration by modifying the debconf configuration:

# Comment out the DPkg preconfigure line
sudo ex +"%s@DPkg@//DPkg" -cwq /etc/apt/apt.conf.d/70debconf

# Or simply remove the file if you don't need debconf at all
sudo rm /etc/apt/apt.conf.d/70debconf

Then reconfigure debconf to use noninteractive mode:

sudo dpkg-reconfigure debconf -f noninteractive -p critical

This is a container-level fix for running systems, but in Docker it's better to set ENV variables.

If you're running apt in interactive mode (not Docker), be careful with stdin redirection:

# BAD - redirects stdin, causes preconfigure to fail
apt-get install -y package < /dev/null

# GOOD - no stdin redirection, relies on -y flag
apt-get install -y package

# BETTER - set environment variable
DEBIAN_FRONTEND=noninteractive apt-get install -y package

The -y flag automatically answers 'yes' to prompts, but debconf still attempts initialization before seeing the flag.

If the error doesn't block your build and you just want to silence it, redirect stderr:

apt-get update 2>/dev/null
apt-get install -y package 2>/dev/null

Or in Dockerfile:

RUN apt-get update 2>/dev/null && \
    apt-get install -y curl 2>/dev/null

Note: This just hides the warning; it's not a proper fix. The recommended approach is to set DEBIAN_FRONTEND.