CODEWITHSUNDEEP
dockeralpine-linux
Daniel Gartmann
Daniel Gartmann

Reputation: 13008

How do I add a user when I'm using Alpine as a base image?

I'm using alpine (or an image that is based on Alpine) as the base image in my Dockerfile. Which instructions do I need to add to create a user?

Eventually I'll use this user to run the application I'll place into the container so that the root user does not.

Upvotes: 306

Views: 323671

Answers (4)

rexypoo
rexypoo

Reputation: 1934

The commands are adduser and addgroup.

Here's a template for Docker you can use in busybox environments (alpine) as well as Debian-based environments (Ubuntu, etc.):

ENV USER=docker
ENV GROUPNAME=$USER
ENV UID=12345
ENV GID=23456

RUN addgroup \
    --gid "$GID" \
    "$GROUPNAME" \
&&  adduser \
    --disabled-password \
    --gecos "" \
    --home "$(pwd)" \
    --ingroup "$GROUPNAME" \
    --no-create-home \
    --uid "$UID" \
    $USER

Note the following:

  • --disabled-password prevents prompt for a password
  • --gecos "" circumvents the prompt for "Full Name" etc. on Debian-based systems
  • --home "$(pwd)" sets the user's home to the WORKDIR. You may not want this.
  • --no-create-home prevents cruft getting copied into the directory from /etc/skel

The usage description for these applications is missing the long flags present in the code for adduser and addgroup.

The following long-form flags should work both in alpine as well as debian-derivatives:

adduser

BusyBox v1.28.4 (2018-05-30 10:45:57 UTC) multi-call binary.

Usage: adduser [OPTIONS] USER [GROUP]

Create new user, or add USER to GROUP

        --home DIR           Home directory
        --gecos GECOS        GECOS field
        --shell SHELL        Login shell
        --ingroup GRP        Group (by name)
        --system             Create a system user
        --disabled-password  Don't assign a password
        --no-create-home     Don't create home directory
        --uid UID            User id

One thing to note is that if --ingroup isn't set then the GID is assigned to match the UID. If the GID corresponding to the provided UID already exists adduser will fail.

addgroup

BusyBox v1.28.4 (2018-05-30 10:45:57 UTC) multi-call binary.

Usage: addgroup [-g GID] [-S] [USER] GROUP

Add a group or add a user to a group

        --gid GID  Group id
        --system   Create a system group

I discovered all of this while trying to write my own alternative to the fixuid project for running containers as the hosts UID/GID.

My entrypoint helper script can be found on GitHub.

The intent is to prepend that script as the first argument to ENTRYPOINT which should cause Docker to infer UID and GID from a relevant bind mount.

An environment variable "TEMPLATE" may be required to determine where the permissions should be inferred from.

(At the time of writing I don't have documentation for my script. It's still on the todo list!!)

Upvotes: 177

Madan Sapkota
Madan Sapkota

Reputation: 26071

Group and User Setup:

Create default values for User ID (UID), Group ID (GID), and username, which can be customized using arguments.

ARG USER_UID=1000
ARG GROUP_GID=1000
ARG UGNAME=webapp

Remove Existing Group and User:

Check for the presence of an existing group and user. If either exists, remove them.

RUN if getent passwd ${USER_UID} >/dev/null; then \
    deluser $(getent passwd ${USER_UID} | cut -d: -f1); fi

RUN if getent group ${GROUP_GID} >/dev/null; then \
    delgroup $(getent group ${GROUP_GID} | cut -d: -f1); fi

Create New Group and User:

Create a new system group and a new system user with the specified UID, GID, and username.

RUN addgroup --system --gid ${GROUP_GID} ${UGNAME}

RUN adduser --system --disabled-password --home /home/${UGNAME} \
    --uid ${USER_UID} --ingroup ${UGNAME} ${UGNAME}

Set the user as the default user for the container. All subsequent commands will run with this user.

USER ${UGNAME}

Upvotes: 4

gavenkoa
gavenkoa

Reputation: 48713

There is package shadow that brings useradd & usermod.

adduser has some stupid limitations:

$ sudo adduser --disabled-password root
adduser: user 'root' in use

but usermod doesn't:

$ sudo apk add shadow
$ sudo usermod --unlock root

Upvotes: 16

Daniel Gartmann
Daniel Gartmann

Reputation: 13008

Alpine uses the command adduser and addgroup for creating users and groups (rather than useradd and usergroup).

FROM alpine:latest

# Create a group and user
RUN addgroup -S appgroup && adduser -S appuser -G appgroup

# Tell docker that all future commands should run as the appuser user
USER appuser

The flags for adduser are:

Usage: adduser [OPTIONS] USER [GROUP]

Create new user, or add USER to GROUP

        -h DIR          Home directory
        -g GECOS        GECOS field
        -s SHELL        Login shell
        -G GRP          Group
        -S              Create a system user
        -D              Don't assign a password
        -H              Don't create home directory
        -u UID          User id
        -k SKEL         Skeleton directory (/etc/skel)

Add new user official docs

Upvotes: 504

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