SFTP

Supported tags and respective Dockerfile links

• debian-jessie, debian, latest (Dockerfile)
• alpine-3.6, alpine (Dockerfile)
• alpine-3.5 (Dockerfile)
• alpine-3.4 (Dockerfile)

Securely share your files

Easy to use SFTP (SSH File Transfer Protocol) server with OpenSSH. This is an automated build linked with the debian and alpine repositories.

Usage

• Required: define users as command arguments, STDIN or mounted in /etc/sftp/users.conf (syntax: user:pass[:e][:uid[:gid[:dir1[,dir2]...]]]...).
  • Set UID/GID manually for your users if you want them to make changes to your mounted volumes with permissions matching your host filesystem.
  • Add directory names at the end, if you want to create them under the user's home directory. Perfect when you just want a fast way to upload something.
• Optional (but recommended): mount volumes.
  • The users are chrooted to their home directory, so you can mount the volumes in separate directories inside the user's home directory (/home/user/mounted-directory) or just mount the whole /home directory. Just remember that the users can't create new files directly under their own home directory, so make sure there are at least one subdirectory if you want them to upload files.
  • For consistent server fingerprint, mount your own host keys (i.e. /etc/ssh/ssh_host_*)

Examples

Simplest docker run example

docker run -p 22:22 -d atmoz/sftp foo:pass:::upload

User "foo" with password "pass" can login with sftp and upload files to a folder called "upload". No mounted directories or custom UID/GID. Later you can inspect the files and use --volumes-from to mount them somewhere else (or see next example).

Sharing a directory from your computer

Let's mount a directory and set UID (we will also provide our own hostkeys):

docker run \
    -v /host/upload:/home/foo/upload \
    -v /host/ssh_host_rsa_key:/etc/ssh/ssh_host_rsa_key \
    -v /host/ssh_host_rsa_key.pub:/etc/ssh/ssh_host_rsa_key.pub \
    -p 2222:22 -d atmoz/sftp \
    foo:pass:1001

Using Docker Compose:

sftp:
    image: atmoz/sftp
    volumes:
        - /host/upload:/home/foo/upload
        - /host/ssh_host_rsa_key:/etc/ssh/ssh_host_rsa_key
        - /host/ssh_host_rsa_key.pub:/etc/ssh/ssh_host_rsa_key.pub
    ports:
        - "2222:22"
    command: foo:pass:1001

Logging in

The OpenSSH server runs by default on port 22, and in this example, we are forwarding the container's port 22 to the host's port 2222. To log in with the OpenSSH client, run: sftp -P 2222 foo@<host-ip>

Store users in config

docker run \
    -v /host/users.conf:/etc/sftp/users.conf:ro \
    -v mySftpVolume:/home \
    -v /host/ssh_host_rsa_key:/etc/ssh/ssh_host_rsa_key \
    -v /host/ssh_host_rsa_key.pub:/etc/ssh/ssh_host_rsa_key.pub \
    -p 2222:22 -d atmoz/sftp

/host/users.conf:

foo:123:1001:100
bar:abc:1002:100
baz:xyz:1003:100

Encrypted password

Add :e behind password to mark it as encrypted. Use single quotes if using terminal.

docker run \
    -v /host/share:/home/foo/share \
    -p 2222:22 -d atmoz/sftp \
    'foo:$1$0G2g0GSt$ewU0t6GXG15.0hWoOX8X9.:e:1001'

Tip: you can use atmoz/makepasswd to generate encrypted passwords:
echo -n "your-password" | docker run -i --rm atmoz/makepasswd --crypt-md5 --clearfrom=-

Logging in with SSH keys

Mount public keys in the user's .ssh/keys/ directory. All keys are automatically appended to .ssh/authorized_keys (you can't mount this file directly, because OpenSSH requires limited file permissions). In this example, we do not provide any password, so the user foo can only login with his SSH key.

docker run \
    -v /host/id_rsa.pub:/home/foo/.ssh/keys/id_rsa.pub:ro \
    -v /host/id_other.pub:/home/foo/.ssh/keys/id_other.pub:ro \
    -v /host/share:/home/foo/share \
    -p 2222:22 -d atmoz/sftp \
    foo::1001

Providing your own SSH host key

This container will generate new SSH host keys at first run. To avoid that your users get a MITM warning when you recreate your container (and the host keys changes), you can mount your own host keys.

docker run \
    -v /host/ssh_host_ed25519_key:/etc/ssh/ssh_host_ed25519_key \
    -v /host/ssh_host_rsa_key:/etc/ssh/ssh_host_rsa_key \
    -v /host/share:/home/foo/share \
    -p 2222:22 -d atmoz/sftp \
    foo::1001

Tip: you can generate your keys with these commands:

ssh-keygen -t ed25519 -f /host/ssh_host_ed25519_key < /dev/null
ssh-keygen -t rsa -b 4096 -f /etc/ssh/ssh_host_rsa_key < /dev/null

Execute custom scripts or applications

Put your programs in /etc/sftp.d/ and it will automatically run when the container starts. See next section for an example.

Bindmount dirs from another location

If you are using --volumes-from or just want to make a custom directory available in user's home directory, you can add a script to /etc/sftp.d/ that bindmounts after container starts.

#!/bin/bash
# File mounted as: /etc/sftp.d/bindmount.sh
# Just an example (make your own)

function bindmount() {
    if [ -d "$1" ]; then
        mkdir -p "$2"
    fi
    mount --bind $3 "$1" "$2"
}

# Remember permissions, you may have to fix them:
# chown -R :users /data/common

bindmount /data/admin-tools /home/admin/tools
bindmount /data/common /home/dave/common
bindmount /data/common /home/peter/common
bindmount /data/docs /home/peter/docs --read-only

What's the difference between Debian and Alpine?

The biggest differences are in size and OpenSSH version. Alpine is 10 times smaller than Debian. OpenSSH version can also differ, as it's two different teams maintaining the packages. Debian is generally considered more stable and only bugfixes and security fixes are added after each Debian release (about 2 years). Alpine has a faster release cycle (about 6 months) and therefore newer versions of OpenSSH. As I'm writing this, Debian has version 6.7 while Alpine has version 7.4. Recommended reading: Comparing Debian vs Alpine for container & Docker apps