{
  "slug": "filesystem-freeze",
  "term": "Filesystem freeze",
  "aliases": [
    "fsfreeze",
    "Filesystem freezing"
  ],
  "definition": "A filesystem freeze temporarily blocks modifications after completing ongoing filesystem transactions and flushing dirty filesystem data, metadata and logs to storage.",
  "note": "Linux fsfreeze requires a mounted filesystem with freeze support; blocked modifications resume after thaw. [util-linux-freeze] QEMU v10.1.0 freezes eligible local guest filesystems and returns a count, which may be zero; its list variant ignores invalid mountpoints. That count does not establish coverage of every application dependency. [qemu-freeze] Filesystem transactions are not application transactions: application preparation is a separate concern. [microsoft-vss]",
  "status": "shipping",
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-15",
  "advantages": [
    {
      "text": "Can establish a stable filesystem image for snapshot-capable storage.",
      "citationIds": [
        "util-linux-freeze"
      ]
    }
  ],
  "limitations": [
    {
      "text": "Writers can remain blocked until thaw; a recovery procedure must account for failed capture and cleanup.",
      "citationIds": [
        "util-linux-freeze"
      ]
    },
    {
      "text": "Files still undergoing unlink can remain represented in the frozen on-disk image until thaw or a clean mount of the snapshot completes.",
      "citationIds": [
        "util-linux-freeze"
      ]
    },
    {
      "text": "A guest-agent status report can be invalidated by another process changing freeze state.",
      "citationIds": [
        "qemu-freeze"
      ]
    }
  ],
  "related": [
    "snapshot",
    "application-consistent-snapshot",
    "application-quiescing",
    "crash-consistency",
    "restore-test"
  ],
  "citations": [
    {
      "id": "util-linux-freeze",
      "title": "util-linux v2.41.2: fsfreeze(8), filesystem freeze and thaw",
      "url": "https://github.com/util-linux/util-linux/blob/v2.41.2/sys-utils/fsfreeze.8.adoc",
      "accessed": "2026-10-15"
    },
    {
      "id": "qemu-freeze",
      "title": "QEMU v10.1.0: guest agent freeze protocol and scope",
      "url": "https://github.com/qemu/qemu/blob/v10.1.0/qga/qapi-schema.json",
      "accessed": "2026-10-15"
    },
    {
      "id": "microsoft-vss",
      "title": "Microsoft: Volume Shadow Copy Service, application writers and snapshot coordination",
      "url": "https://learn.microsoft.com/en-us/windows-server/storage/file-server/volume-shadow-copy-service",
      "accessed": "2026-10-15"
    },
    {
      "id": "hesela-recovery",
      "title": "Hesela: Snapshots and backups: which failures can you recover from?",
      "url": "https://hesela.com/analyses/snapshot-backup-recovery-boundaries/",
      "accessed": "2026-10-15"
    }
  ]
}