Easy to use SFTP (SSH File Transfer Protocol) server with OpenSSH.
- Define users in (1) command arguments, (2)
SFTP_USERSenvironment variable or (3) in file mounted as/etc/sftp/users.conf(syntax:user:pass[:e][:uid[:gid[:dir1[,dir2]...]]] ..., see below for examples)- Set UID/GID manually for your users if you want them to make changes to your mounted volumes with permissions matching your host filesystem.
- Directory names at the end will be created under user's home directory with write permission, if they aren't already present.
- 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_*)
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).
Let's mount a directory and set UID:
docker run \
-v <host-dir>/upload:/home/foo/upload \
-p 2222:22 -d atmoz/sftp \
foo:pass:1001
sftp:
image: atmoz/sftp
volumes:
- <host-dir>/upload:/home/foo/upload
ports:
- "2222:22"
command: foo:pass:1001
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>
docker run \
-v <host-dir>/users.conf:/etc/sftp/users.conf:ro \
-v mySftpVolume:/home \
-p 2222:22 -d atmoz/sftp
/users.conf:
foo:123:1001:100
bar:abc:1002:100
baz:xyz:1003:100
Add :e behind password to mark it as encrypted. Use single quotes if using terminal.
docker run \
-v <host-dir>/share:/home/foo/share \
-p 2222:22 -d atmoz/sftp \
'foo:$1$0G2g0GSt$ewU0t6GXG15.0hWoOX8X9.:e:1001'
Tip: you can use this Python code to generate encrypted passwords:
docker run --rm python:alpine python -c "import crypt; print(crypt.crypt('YOUR_PASSWORD'))"
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-dir>/id_rsa.pub:/home/foo/.ssh/keys/id_rsa.pub:ro \
-v <host-dir>/id_other.pub:/home/foo/.ssh/keys/id_other.pub:ro \
-v <host-dir>/share:/home/foo/share \
-p 2222:22 -d atmoz/sftp \
foo::1001
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-dir>/ssh_host_ed25519_key:/etc/ssh/ssh_host_ed25519_key \
-v <host-dir>/ssh_host_rsa_key:/etc/ssh/ssh_host_rsa_key \
-v <host-dir>/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 ssh_host_ed25519_key < /dev/null
ssh-keygen -t rsa -b 4096 -f ssh_host_rsa_key < /dev/null
Put your programs in /etc/sftp.d/ and it will automatically run when the container starts.
See next section for an example.
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
NOTE: Using mount requires that your container runs with the CAP_SYS_ADMIN capability turned on. See this answer for more information.
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 7.4 while Alpine has version 7.5. Recommended reading: Comparing Debian vs Alpine for container & Docker apps
It depends on which linux distro and version you choose (see available images at the top). You can see what version you get by checking the distro's packages online. I have provided direct links below for easy access.
Images are automatically built daily to get the newest version of OpenSSH provided by the package managers.
