alexs77/vsftpd

vsftpd FTP Server for Docker

Note on Security: This container has been developed primarily for local and development environments and should not be used in a production environment without rigorous security review and customisation.

This Docker image provides a vsftpd server, incorporating the following core features:

• Based on the debian:bookworm-slim image.
• Support for Virtual Users, allowing the specification of a custom home directory (local_root) and associated system user ID (FTP_UID).
• Passive Mode (PASV) only - Active FTP is completely disabled for enhanced security.

The pre-built image is available on Docker Hub at https://hub.docker.com/r/alexs77/vsftpd.

Attribution

This work is based on the foundation laid by https://github.com/wildscamp/docker-vsftpd. For reference, their Docker registry page is available at https://hub.docker.com/r/wildscamp/vsftpd/.

Table of Contents

• vsftpd FTP Server for Docker
  • Attribution
  • Table of Contents
  • Configuration
    • Environment Variables
      • VSFTPD_USER_[0-9]+
        • Examples
        • Caveats
      • VSFTPD_CONF_*
        • Examples
      • VSFTPD_CONF
      • PASV_ADDRESS
        • Common Values
      • PASV_MIN_PORT
      • PASV_MAX_PORT
  • Ports
  • Volumes
    • Logging

Configuration

This image supports run-time configuration via standard environment variables.

Environment Variables

VSFTPD_USER_[0-9]+

These are compound variables that enable the addition of an arbitrary number of virtual FTP users.

• Accepted format: A string in the format <username>:<password>:<system_uid>:<ftp_root_dir>.
• Description: The <system_uid> and <ftp_root_dir> parameters are optional, but the separating colons (:) must be maintained. If the system user ID is omitted, it defaults to the UID of the built-in ftp account (104). If the root directory is omitted, it defaults to /home/virtual/<username>.

Examples

• VSFTPD_USER_1=hello:world:: - Creates an FTP user hello with the password world. The system user's UID will default to 104, and the FTP root directory will be /home/virtual/hello.
• VSFTPD_USER_1=user1:docker:33: - Creates an FTP user user1 with the password docker. The system user's UID will be 33. If a system user with this ID already exists, the FTP user will be mapped to it. The FTP root directory defaults to /home/virtual/user1.
• VSFTPD_USER_1=mysql:mysql:999:/srv/ftp/mysql - Creates an FTP user mysql with the password mysql. The system user's UID is 999, and the FTP root directory is explicitly set to /srv/ftp/mysql.

Caveats

• Reserved Username: vsftpd applies special handling to the FTP username ftp. It is therefore recommended to avoid using this name when defining a virtual FTP user.
• Writable Root: The container configures allow_writeable_chroot=YES in the default user configuration.

VSFTPD_CONF_*

These variables allow you to set arbitrary vsftpd configuration options without modifying configuration files.

• Pattern: Any environment variable prefixed with VSFTPD_CONF_ will be automatically converted to a vsftpd configuration directive.
• Processing: The prefix VSFTPD_CONF_ is stripped, the remaining name is converted to lowercase, and the result is written to the vsftpd configuration file.
• Target file: The configuration file path is determined by the VSFTPD_CONF variable (defaults to /etc/vsftpd/vsftpd.conf).

Examples

• VSFTPD_CONF_DUAL_LOG_ENABLE=YES - Sets dual_log_enable=YES in the vsftpd configuration, enabling dual logging mode.
• VSFTPD_CONF_MAX_CLIENTS=50 - Sets max_clients=50, limiting the maximum number of simultaneous clients.
• VSFTPD_CONF_IDLE_SESSION_TIMEOUT=600 - Sets idle_session_timeout=600, terminating idle sessions after 10 minutes.
• VSFTPD_CONF_WRITE_ENABLE=NO - Sets write_enable=NO, creating a read-only FTP server.

Note: These settings are applied during container startup and will override any existing values in the configuration file.

VSFTPD_CONF

• Default value: /etc/vsftpd/vsftpd.conf
• Accepted values: A valid file path within the container.
• Description: Specifies the vsftpd configuration file to which VSFTPD_CONF_* variables will write their settings. This allows you to target a custom configuration file if needed.

PASV_ADDRESS

• Accepted values: The DNS name or IP address used by the FTP client to connect to this container.
• Description: This variable instructs vsftpd as to which address it should advertise to clients for passive mode data connections. Setting an IP address is recommended, as the container's DNS resolution may not be identical to the Docker host's.
• Notes:
  • This parameter is required for proper FTP operation since only passive mode is supported. vsftpd will automatically advertise the internal Docker IP of the interface on which the connection was received, which is usually unreachable from the client host.
  • It used to be a dedicated environment variable, but can now also be set via VSFTPD_CONF_PASV_ADDRESS for consistency with other vsftpd settings.

Common Values

PASV_MIN_PORT

• Default value: 30000
• Accepted values: An integer lower than PASV_MAX_PORT.
• Description: The minimum port number to be used for passive connections.

PASV_MAX_PORT

• Default value: 30009
• Accepted values: An integer higher than PASV_MIN_PORT.
• Description: The maximum port number to be used for passive connections.

Ports

The container exposes the following ports:

• Port 21/tcp: FTP Control (Command Channel)
• Ports 30000-30009/tcp: Passive Mode (PASV) data ports. This range is defined by the default values for PASV_MIN_PORT and PASV_MAX_PORT.

Note: Active FTP mode is completely disabled. Port 20 is not exposed or used.

When running the container, ensure all necessary ports are published to your host machine using the -p flag or in your docker-compose.yaml.

Volumes

For the FTP server to be useful, a minimum of one data volume should be mounted.

• Data Directories: The FTP user's root directory must be mounted from the host system or a named volume. For example, a user with local_root=/home/virtual/user1 will require a volume mount at /home/virtual/user1 inside the container.
• Log Directory: The container writes logs to /var/log/vsftpd. It is recommended to mount this directory to retain logs outside of the container lifecycle.
• Configuration Overrides: An individual user's configuration can be overridden by mounting a vsftpd configuration file to /etc/vsftpd/vusers/<username>. Global default settings can be overridden by mounting a file to /etc/vsftpd/default_user.conf.

Logging

The vsftpd server writes log files to the /var/log/vsftpd directory inside the container:

• /var/log/vsftpd/vsftpd.log - Main vsftpd log file containing FTP protocol commands, responses, and connection details (when log_ftp_protocol=YES)
• /var/log/vsftpd/xferlog - File transfer log recording all upload and download operations

To persist logs on the host system and enable access outside the container, mount the log directory as a volume: