fsfreeze
Suspend or resume access to a filesystem.
Synopsis
fsfreeze --freeze <mountpoint>
fsfreeze --unfreeze <mountpoint>
Operation
--freeze: Suspends all new writes to the filesystem, flushes all dirty data/metadata/log to disk, and blocks any process that attempts to write until unfrozen. Uses theFIFREEZEioctl.--unfreeze: Resumes normal filesystem operations and unblocks waiting writers. Uses theFITHAWioctl.
Inputs
<mountpoint>— path to a mounted filesystem directory
Outputs
None. The tool operates purely via ioctls on the mountpoint.
Syscalls / ioctls
| ioctl | Value | Description |
|---|---|---|
FIFREEZE | 0xc0045877 | Freeze filesystem (halt writes, flush to disk) |
FITHAW | 0xc0045878 | Thaw (unfreeze) filesystem |
Both ioctls take an int argument of 0.
Command-line options
| Option | Description |
|---|---|
-f, --freeze | Freeze the filesystem |
-u, --unfreeze | Unfreeze the filesystem |
-h, --help | Display help |
-V, --version | Display version |
Exactly one of --freeze or --unfreeze must be specified.
Exit codes
| Code | Meaning |
|---|---|
| 0 | Success |
| 1 | Failure (permission denied, not a mountpoint, ioctl error) |
Permissions
Requires root privileges.
Supported filesystems
btrfs, ext2/3/4, f2fs, jfs, nilfs2, reiserfs, xfs.
Notes
- The filesystem must be mounted.
- Device-mapper (LVM) automatically freezes/thaws on snapshot creation; manual freeze is unnecessary.
- Useful for creating consistent backups of the underlying block device.