'\" t
.\"     Title: btrfs-zero-log
.\"    Author: [FIXME: author] [see http://docbook.sf.net/el/author]
.\" Generator: DocBook XSL Stylesheets v1.78.1 <http://docbook.sf.net/>
.\"      Date: 11/22/2014
.\"    Manual: Btrfs Manual
.\"    Source: Btrfs v3.17
.\"  Language: English
.\"
.TH "BTRFS\-ZERO\-LOG" "8" "11/22/2014" "Btrfs v3\&.17" "Btrfs Manual"
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.SH "NAME"
btrfs-zero-log \- clear out log tree
.SH "SYNOPSIS"
.sp
\fBbtrfs\-zero\-log\fR \fI<dev>\fR
.SH "DESCRIPTION"
.sp
\fBbtrfs\-zero\-log\fR will remove the log tree if log tree is corrupt, which will allow you to mount the filesystem again\&.
.sp
The common case where this happens has been fixed a long time ago, so it is unlikely that you will see this particular problem\&.
.sp
One can determine whether \fBbtrfs\-zero\-log\fR is needed according to the kernel backtrace:
.sp
.if n \{\
.RS 4
.\}
.nf
? 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]
.fi
.if n \{\
.RE
.\}
.sp
If the errors are like above, then \fBbtrfs\-zero\-log\fR should be used to clear the log and the filesystem may be mounted normally again\&.
.if n \{\
.sp
.\}
.RS 4
.it 1 an-trap
.nr an-no-space-flag 1
.nr an-break-flag 1
.br
.ps +1
\fBNote\fR
.ps -1
.br
.sp
If you use btrfs as the root filesystem, you may want to include \fBbtrfs\-zero\-log\fR into initramdisk if the log problems hits you often\&.
.sp .5v
.RE
.SH "EXIT STATUS"
.sp
\fBbtrfs\-zero\-log\fR will return 0 if no error happened\&. Other exit code means some problems happened\&.
.SH "SEE ALSO"
.sp
\fBmkfs\&.btrfs\fR(8)