{
  "slug": "mount-propagation",
  "term": "Mount propagation",
  "aliases": [
    "Linux mount propagation",
    "Shared subtree propagation"
  ],
  "definition": "Mount propagation controls whether mount and unmount events are replicated between related Linux mounts.",
  "note": "Shared mounts exchange events within a peer group. A slave receives events from its master peer group without sending them back upstream; it may also be shared with its own peer group. Private mounts neither send nor receive propagated events. An unbindable mount blocks propagation in both directions and cannot be bind-mounted. [shared]\n\nPropagation concerns events immediately beneath each mount, not replication of file contents. Descendant mounts have their own settings; changing one mount to private does not recursively privatize them. Namespace cloning can retain shared relationships, so a separate namespace is not by itself an event-isolation guarantee. [namespaces]\n\n/proc/PID/mountinfo exposes optional shared and master tags; both can occur for a shared-and-slave mount. A private mount has none of the recognized propagation tags. These fields describe topology, separately from per-mount and superblock access flags. [mountinfo] A private tree does not freeze data reachable through another writable attachment. [shared] [mount-manual]",
  "related": [
    "mount-namespace",
    "bind-mount",
    "read-only-mount"
  ],
  "citations": [
    {
      "id": "shared",
      "title": "Linux kernel documentation: Shared Subtrees, shared, slave, private and unbindable mounts",
      "url": "https://docs.kernel.org/filesystems/sharedsubtree.html",
      "accessed": "2026-11-04"
    },
    {
      "id": "namespaces",
      "title": "Linux man-pages: mount_namespaces(7), immediate event scope and namespace copies",
      "url": "https://man7.org/linux/man-pages/man7/mount_namespaces.7.html",
      "accessed": "2026-11-04"
    },
    {
      "id": "mountinfo",
      "title": "Linux man-pages: proc_pid_mountinfo(5), propagation tags and option layers",
      "url": "https://man7.org/linux/man-pages/man5/proc_pid_mountinfo.5.html",
      "accessed": "2026-11-04"
    },
    {
      "id": "mount-manual",
      "title": "util-linux v2.41.1: mount(8), bind mounts and read-only setting notes",
      "url": "https://kernel.googlesource.com/pub/scm/utils/util-linux/util-linux/+/refs/tags/v2.41.1/sys-utils/mount.8.adoc",
      "accessed": "2026-11-04"
    }
  ],
  "status": "shipping",
  "advantages": [],
  "limitations": [],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-11-04",
  "provenance": [
    "Documentation synthesis from primary Linux sources checked on the access date; no privileged mounting, namespace experiment or device-write measurement was performed.",
    "The file-content boundary combines the topology rules with the documented semantics of writable bind attachments; it is an interpretive synthesis, not a device observation."
  ]
}