image-format.md

Image format

Enroot container images are standard squashfs images with the following configuration files influencing the container runtime behavior:

File	Description
/etc/rc	Command script of the container (entrypoint)
/etc/fstab	Mount configuration of the container
/etc/environment	Environment of the container

These files follow the same format as the standard Linux/Unix ones (see fstab(5), rc(8), pam_env(8)) with the exceptions listed below.

• /etc/rc:

  • The command and arguments of the start command are passed as input parameters.

• /etc/fstab:

  • The target mountpoint is relative to the container rootfs.
  • Allows some fields to be omitted where it makes sense, for example /proc /proc rbind or tmpfs /tmp are valid fstab entries.
  • Adds the mount options x-create=dir, x-create=file and x-create=auto to create an empty directory or file before performing the mount.
  • Adds the mount options x-move and x-detach to move or detach a mountpoint respectively.
  • References to environment variables from the host of the form ${ENVVAR} will be substituted.
  • The fs_freq field is ignored and the fs_passno is instead used to specify a specific mount order.

# Example mounting the current working directory from the host inside the container
${PWD} /mnt none x-create=dir,bind

• /etc/environment:
  • References to environment variables from the host of the form ${ENVVAR} will be substituted.

# Example preserving the DISPLAY environment variable from the host
DISPLAY=${DISPLAY}