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Mount Option

ruri supports mounting various types of resources into the container, with advanced mount types and flags.

Syntax

-m [source] [target]
-M [source] [target]
  • -m: Mount a resource at the specified target path.
  • -M: Same as -m, but enforces read-only. In the new version, you can also use the RDONLY: prefix instead.

The target path is always interpreted relative to the container's filesystem (not the host). If the target does not exist in the container, it will be created automatically.

Source Types

Depending on the type of source, different mount strategies are applied:

  1. Directory
    If the source is a directory on the host, it will be bind-mounted into the container at the target.

  2. Image File
    If the source is a regular file recognized as a disk image, it will be mounted via a loop device at the target.

  3. Block Device
    If the source is a block device (e.g., /dev/sdb1), it will be mounted directly at the target.

  4. Other Regular Files
    If the source is a file that is not a recognized image, it will be bind-mounted as a file at the target.

  5. Special Mount Sources

    • tmpfs
      Specify with format:

      TMPFS:size=[size]

      Mounts a tmpfs at the target with the given size (e.g., TMPFS:size=100M).
      Note: The size can be specified in bytes, kilobytes (K), megabytes (M), or gigabytes (G).
      TMPFS: without size defaults to kernel behavior.

    • overlayfs
      Specify with format:

      OVERLAY:lowerdir=/path/to/lower,upperdir=/path/to/upper,workdir=/path/to/work

      Mounts an overlay filesystem at the target using the specified options.

      • Volatile rootfs You can create a tmpfs overlay for rootfs, and all changes will be lost after the container stops. 
        root@studio:/home/moehacker/ruri# mkdir /tmp/ruri
root@studio:/home/moehacker/ruri# mount -t tmpfs tmpfs /tmp/ruri
root@studio:/home/moehacker/ruri# mkdir /tmp/ruri/upper
root@studio:/home/moehacker/ruri# mkdir /tmp/ruri/work
root@studio:/home/moehacker/ruri# ./ruri -m OVERLAY:lowerdir=/home/moehacker/alpine,upperdir=/tmp/ruri/upper,workdir=/tmp/ruri/work / /tmp/ruri/work

    • filesystem

      • EXT4: Mounts an ext4 filesystem at the target.
      • FAT32: Mounts a FAT32 (vfat) filesystem at the target.
      • NTFS: Mounts an NTFS filesystem at the target.
      • XFS: Mounts an XFS filesystem at the target.
      • BTRFS: Mounts a Btrfs filesystem at the target.
      • EXFAT: Mounts an exFAT filesystem at the target.
      • F2FS: Mounts an F2FS filesystem at the target.
      • EROFS: Mounts an EROFS filesystem at the target.

      Example:

      -m EXT4:/dev/sdb1 /mnt/data

      This mounts /dev/sdb1 as an ext4 filesystem at /mnt/data.

Behavior:

For image files and block devices, if the filesystem type is not specified in prefix, ruri will attempt to auto-detect the filesystem type by trying all nodev filesystems in your /proc/filesystems.

Mount Flags

Mount flags can be set using prefixes in the source string. Prefixes are colon-separated.

Example:

-m RDONLY:NOEXEC:/dev/sdb1 /mnt/disk

This mounts /dev/sdb1 at /mnt/disk as read-only and with the noexec flag enabled.

Supported Flags

Prefix Description
RDONLY Mount read-only (same as -M)
NOSUID Do not allow set-user-ID or set-group-ID
NOEXEC Do not allow execution of binaries
NODIRATIME Do not update directory access times
NOATIME Do not update access times
SYNCHRONOUS Writes are synced immediately
DIRSYNC Directory updates are synchronous
MANDLOCK Enable mandatory locking
RELATIME Update access time relative to modification
SLAVE Make mount a slave in shared subtree
SHARED Make mount a shared subtree
PRIVATE Make mount private
UNBINDABLE Prevent remounting elsewhere
SILENT Suppress mount errors in logs (if supported)
POSIXACL Enable POSIX ACLs
LAZYTIME Delay access/modify time updates

Notes:

  • Prefixes are order-insensitive but must be placed before the source path.
  • If the source does not exist or cannot be recognized, the mount will fail.
  • To ensure container isolation and prevent security risks, custom mounting of special filesystems such as proc, sysfs, debugfs, or similar filesystems is not permitted. If required, you can manually modify the implementation of mount_other_type() in src/mount.c.