# btrfs-rescue

## NAME



           btrfs-rescue - Recover a damaged btrfs filesystem
    


## SYNOPSIS



           **btrfs rescue** _< subcommand> <args>_
    


## DESCRIPTION



           **btrfs rescue** is used to try to recover a damaged btrfs filesystem.
    


## SUBCOMMAND



           **chunk-recover**[options] _< device>_
               Recover the chunk tree by scanning the devices
    
               **Options**
    
               -y
                   assume an answer of _yes_ to all questions.
    
               -h
                   help.
    
               -v
                   (deprecated) alias for global _-v_ option
    
               **Note**
    
               Since **chunk-recover** will scan the whole device, it will be
               **VERY** slow especially executed on a large device.
    
           **fix-device-size** _< device>_
               fix device size and super block total bytes values that are do
               not match
    
               Kernel 4.11 starts to check the device size more strictly and
               this might mismatch the stored value of total bytes. See the
               exact error message below. Newer kernel will refuse to mount
               the filesystem where the values do not match. This error is
               not fatal and can be fixed. This command will fix the device
               size values if possible.
    
                   BTRFS error (device sdb): super_total_bytes 92017859088384 mismatch with fs_devices total_rw_bytes 92017859094528
    
               The mismatch may also exhibit as a kernel warning:
    
                   WARNING: CPU: 3 PID: 439 at fs/btrfs/ctree.h:1559 btrfs_update_device+0x1c5/0x1d0 [btrfs]
    
           **clear-uuid-tree** _< device>_
               Clear uuid tree, so that kernel can re-generate it at next
               read-write mount.
    
               Since kernel v4.16 there and more sanity check performed, and
               sometimes non-critical trees like uuid tree can cause problems
               and reject the mount. In such case, clearing uuid tree may
               make the filesystem to be mountable again without much risk as
               it’s built from other trees.
    
           **super-recover**[options] _< device>_
               Recover bad superblocks from good copies.
    
               **Options**
    
               -y
                   assume an answer of _yes_ to all questions.
    
               -v
                   (deprecated) alias for global _-v_ option
    
           **zero-log** _< device>_
               clear the filesystem log tree
    
               This command will clear the filesystem log tree. This may fix
               a specific set of problem when the filesystem mount fails due
               to the log replay. See below for sample stacktraces that may
               show up in system log.
    
               The common case where this happens was fixed a long time ago,
               so it is unlikely that you will see this particular problem,
               but the command is kept around.
    
                   **Note**
                   clearing the log may lead to loss of changes that were
                   made since the last transaction commit. This may be up to
                   30 seconds (default commit period) or less if the commit
                   was implied by other filesystem activity.
               One can determine whether **zero-log** is needed according to the
               kernel backtrace:
    
                   ? replay_one_dir_item+0xb5/0xb5 [btrfs]
                   ? walk_log_tree+0x9c/0x19d [btrfs]
                   ? btrfs_read_fs_root_no_radix+0x169/0x1a1 [btrfs]
                   ? btrfs_recover_log_trees+0x195/0x29c [btrfs]
                   ? replay_one_dir_item+0xb5/0xb5 [btrfs]
                   ? btree_read_extent_buffer_pages+0x76/0xbc [btrfs]
                   ? open_ctree+0xff6/0x132c [btrfs]
    
               If the errors are like above, then **zero-log** should be used to
               clear the log and the filesystem may be mounted normally
               again. The keywords to look for are _open_ctree_ which says that
               it’s during mount and function names that contain _replay_ ,
               _recover_ or _log_tree_.
    


## EXIT STATUS



           **btrfs rescue** returns a zero exit status if it succeeds. Non zero
           is returned in case of failure.
    


## AVAILABILITY



           **btrfs** is part of btrfs-progs. Please refer to the btrfs wiki
           **http://btrfs.wiki.kernel.org******for further details.


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