.\" See file COPYING in distribution for details.
-.TH MDMON 8 "" v3.1.1
+.TH MDMON 8 "" v4.1-rc2
.SH NAME
mdmon \- monitor MD external metadata arrays
.SH SYNOPSIS
-.BI mdmon " [--all] [--takeover] CONTAINER"
+.BI mdmon " [--all] [--takeover] [--foreground] CONTAINER"
.SH OVERVIEW
The 2.6.27 kernel brings the ability to support external metadata arrays.
is introduced.
.I Mdmon
is tasked with polling the sysfs namespace looking for changes in
-.BR array_state ,
+.BR array_state ,
.BR sync_action ,
and per disk
.BR state
External metadata formats, like DDF, differ from the native MD metadata
formats in that they define a set of disks and a series of sub-arrays
within those disks. MD metadata in comparison defines a 1:1
-relationship between a set of block devices and a raid array. For
-example to create 2 arrays at different raid levels on a single
+relationship between a set of block devices and a RAID array. For
+example to create 2 arrays at different RAID levels on a single
set of disks, MD metadata requires the disks be partitioned and then
-each array can created be created with a subset of those partitions. The
+each array can be created with a subset of those partitions. The
supported external formats perform this disk carving internally.
.P
Container devices simply hold references to all member disks and allow
device to monitor. It can be a full path like /dev/md/container, or a
simple md device name like md127.
.TP
+.B \-\-foreground
+Normally,
+.I mdmon
+will fork and continue in the background. Adding this option will
+skip that step and run
+.I mdmon
+in the foreground.
+.TP
.B \-\-takeover
This instructs
.I mdmon
each of them if appropriate. This is normally used with
.B \-\-takeover
late in the boot sequence.
+A separate
+.I mdmon
+process is started for each container as the
+.B \-\-all
+argument is over-written with the name of the container. To allow for
+containers with names longer than 5 characters, this argument can be
+arbitrarily extended, e.g. to
+.BR \-\-all-active-arrays .
+.TP
.PP
Note that
is automatically started by
.I mdadm
when needed and so does not need to be considered when working with
-RAID arrays. The only times it is run other that by
+RAID arrays. The only times it is run other than by
.I mdadm
is when the boot scripts need to restart it after mounting the new
root filesystem.
+.SH START UP AND SHUTDOWN
+
+As
+.I mdmon
+needs to be running whenever any filesystem on the monitored device is
+mounted there are special considerations when the root filesystem is
+mounted from an
+.I mdmon
+monitored device.
+Note that in general
+.I mdmon
+is needed even if the filesystem is mounted read-only as some
+filesystems can still write to the device in those circumstances, for
+example to replay a journal after an unclean shutdown.
+
+When the array is assembled by the
+.B initramfs
+code, mdadm will automatically start
+.I mdmon
+as required. This means that
+.I mdmon
+must be installed on the
+.B initramfs
+and there must be a writable filesystem (typically tmpfs) in which
+.B mdmon
+can create a
+.B .pid
+and
+.B .sock
+file. The particular filesystem to use is given to mdmon at compile
+time and defaults to
+.BR /run/mdadm .
+
+This filesystem must persist through to shutdown time.
+
+After the final root filesystem has be instantiated (usually with
+.BR pivot_root )
+.I mdmon
+should be run with
+.I "\-\-all \-\-takeover"
+so that the
+.I mdmon
+running from the
+.B initramfs
+can be replaced with one running in the main root, and so the
+memory used by the initramfs can be released.
+
+At shutdown time,
+.I mdmon
+should not be killed along with other processes. Also as it holds a
+file (socket actually) open in
+.B /dev
+(by default) it will not be possible to unmount
+.B /dev
+if it is a separate filesystem.
+
.SH EXAMPLES
-.B " mdmon \-\-all \-\-takeover"
+.B " mdmon \-\-all-active-arrays \-\-takeover"
.br
Any
.I mdmon
which is currently running is killed and a new instance is started.
-This should be run late in the boot sequence and particularly after
-.B /var
-is mounted and writable.
+This should be run during in the boot sequence if an initramfs was
+used, so that any mdmon running from the initramfs will not hold
+the initramfs active.
.SH SEE ALSO
.IR mdadm (8),
.IR md (4).