freeze_super(9) [centos man page]

FREEZE_SUPER(9) 						   The Linux VFS						   FREEZE_SUPER(9)

NAME

       freeze_super - lock the filesystem and force it into a consistent state

SYNOPSIS

       int freeze_super(struct super_block * sb);

ARGUMENTS

       sb
	   the super to lock

DESCRIPTION

       Syncs the super to make sure the filesystem is consistent and calls the fs's freeze_fs. Subsequent calls to this without first thawing the
       fs will return -EBUSY.

       During this function, sb->s_writers.frozen goes through these values:

SB_UNFROZEN
       File system is normal, all writes progress as usual.

SB_FREEZE_WRITE
       The file system is in the process of being frozen. New writes should be blocked, though page faults are still allowed. We wait for all
       writes to complete and then proceed to the next stage.

SB_FREEZE_PAGEFAULT
       Freezing continues. Now also page faults are blocked but internal fs threads can still modify the filesystem (although they should not
       dirty new pages or inodes), writeback can run etc. After waiting for all running page faults we sync the filesystem which will clean all
       dirty pages and inodes (no new dirty pages or inodes can be created when sync is running).

SB_FREEZE_FS
       The file system is frozen. Now all internal sources of fs modification are blocked (e.g. XFS preallocation truncation on inode reclaim).
       This is usually implemented by blocking new transactions for filesystems that have them and need this additional guard. After all internal
       writers are finished we call ->freeze_fs to finish filesystem freezing. Then we transition to SB_FREEZE_COMPLETE state. This state is
       mostly auxiliary for filesystems to verify they do not modify frozen fs.

       sb->s_writers.frozen is protected by sb->s_umount.

COPYRIGHT

Kernel Hackers Manual 3.10					     June 2014							   FREEZE_SUPER(9)

xfs_freeze(8)						      System Manager's Manual						     xfs_freeze(8)

NAME

       xfs_freeze - suspend access to an XFS filesystem

SYNOPSIS

       xfs_freeze -f | -u mount-point

DESCRIPTION

       xfs_freeze suspends and resumes access to an XFS filesystem (see xfs(5)).

       xfs_freeze  halts  new access to the filesystem and creates a stable image on disk.  xfs_freeze is intended to be used with volume managers
       and hardware RAID devices that support the creation of snapshots.

       The mount-point argument is the pathname of the directory where the filesystem is mounted.  The filesystem must be  mounted  to	be  frozen
       (see mount(8)).

       The  -f flag requests the specified XFS 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.

       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.

       The  -u	flag  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.

       One of -f or -u must be supplied to xfs_freeze.

NOTES

       A copy of a frozen XFS filesystem will usually have the same universally unique identifier (UUID) as the original, and  thus  may  be  pre-
       vented from being mounted.  The XFS nouuid mount option can be used to circumvent this issue.

       In  Linux  kernel version 2.6.29, the interface which XFS uses to freeze and unfreeze was elevated to the VFS, so that this tool can now be
       used on many other Linux filesystems.

SEE ALSO

       xfs(5), lvm(8), mount(8).

																     xfs_freeze(8)