File: fsfreeze.8

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.TH FSFREEZE 8 "July 2014" "util-linux" "System Administration"
.SH NAME
fsfreeze \- suspend access to a filesystem (Ext3/4, ReiserFS, JFS, XFS)
.SH SYNOPSIS
.B fsfreeze
.BR \--freeze | \--unfreeze
.I mountpoint

.SH DESCRIPTION
.B fsfreeze
suspends or resumes access to a filesystem.
.PP
.B fsfreeze
halts any new access to the filesystem and creates a stable image on disk.
.B fsfreeze
is intended to be used with hardware RAID devices that support the creation
of snapshots.
.PP
.B fsfreeze
is unnecessary for
.B device-mapper
devices.  The device-mapper (and LVM) automatically freezes a filesystem
on the device when a snapshot creation is requested.
For more details see the
.BR dmsetup (8)
man page.
.PP
The
.I mountpoint
argument is the pathname of the directory where the filesystem
is mounted.
The filesystem must be mounted to be frozen (see
.BR mount (8)).
.PP
Note that access-time updates are also suspended if the filesystem is mounted with
the traditional atime behavior (mount option \fBstrictatime\fR, for more details see
.BR mount (8)).

.SH OPTIONS
.TP
.BR \-f , " \-\-freeze"
This option requests the specified a filesystem to be frozen from new
modifications.  When this is selected, all ongoing transactions in the
filesystem are allowed to complete, new write system calls are halted, other
calls which modify the filesystem are halted, and all dirty data, metadata, and
log information are written to disk.  Any process attempting to write to the
frozen filesystem will block waiting for the filesystem to be unfrozen.
.sp
Note that even after freezing, the on-disk filesystem can contain
information on files that are still in the process of unlinking.
These files will not be unlinked until the filesystem is unfrozen
or a clean mount of the snapshot is complete.
.TP
.BR \-u , " \-\-unfreeze"
This option is used to un-freeze the filesystem and allow operations to
continue.  Any filesystem modifications that were blocked by the freeze are
unblocked and allowed to complete.
.TP
.BR \-V , " \-\-version"
Display version information and exit.
.TP
.BR \-h , " \-\-help"
Display help text and exit.
.SH FILESYSTEM SUPPORT
This command will work only if filesystem supports has support for freezing.
List of these filesystems include (2016-12-18)
.BR btrfs ,
.BR ext2/3/4 ,
.BR f2fs ,
.BR jfs ,
.BR nilfs2 ,
.BR reiserfs ,
and
.BR xfs .
Previous list may be incomplete, as more filesystems get support.  If in
doubt easiest way to know if a filesystem has support is create a small
loopback mount and test freezing it.
.SH AUTHOR
.PP
Written by Hajime Taira.
.SH NOTES
.PP
This man page is based on
.BR xfs_freeze (8).
.SH SEE ALSO
.BR mount (8)
.SH AVAILABILITY
The fsfreeze command is part of the util-linux package and is available from
https://www.kernel.org/pub/linux/utils/util-linux/.