Ubuntu Manpage: ploop - ploop device management utility

NAME

       ploop - ploop device management utility

SYNOPSIS

       ploop init -s size [-f format] [-v version] [-t fstype] [-b blocksize] [-B fsblocksize]
                  [--nolazy] delta_file

       ploop mount [-r] [-F] [-f format] [-b blocksize] [-d device] [-m mount_point]
                   [-o mount_options] [-t fstype] base_delta [...  top_delta]

       ploop mount [-r] [-F] [-d device] [-m mount_point] [-o mount_options] [-t fstype]
                   [-u uuid] DiskDescriptor.xml

       ploop umount { -d device | -m mount_point | DiskDescriptor.xml | image_file }

       ploop replace { -u uuid | -l level | -o cur_image_file } [--keep-name] -i image_file
                     DiskDescriptor.xml

       ploop resize -s size DiskDescriptor.xml

       ploop convert { -f format | -v version } DiskDescriptor.xml

       ploop check [-u uuid] DiskDescriptor.xml

       ploop check [--force] [--hard-force] [--check] [--ro] [--silent] [--drop-inuse] [--raw]
                   [--blocksize size] [--repair-sparse] image_file

       ploop info [-s] [-d] DiskDescriptor.xml

       ploop list [-a]

       ploop snapshot [-u uuid] DiskDescriptor.xml

       ploop snapshot-merge [-u uuid [-U uuid2] | -A] [-n new_delta] DiskDescriptor.xml

       ploop snapshot-switch -u uuid DiskDescriptor.xml

       ploop snapshot-delete -u uuid DiskDescriptor.xml

       ploop snapshot-list [-H] [-u uuid] [-s] [-o field[,field...]]  DiskDescriptor.xml

       ploop copy -s device [-F stop_command] { [-d file] | [-o output_fd] [-f feedback_fd] }

       ploop copy -d file [-i input_fd] [-f feedback_fd]

       ploop balloon discard [--automount] [--to-free size] [--min-block min_size] [--defrag]
                             DiskDescriptor.xml

       ploop restore-descriptor -f format [-b blocksize] disk_dir delta_file

DESCRIPTION

       ploop  is  a  kernel  block  device,  similar  to  the  traditional  loop device (which is
       controlled by losetup(8)) but with  more  features  added,  such  as  dynamic  disk  space
       allocation,  stackable  images,  online  resize,  snapshotting,  and live migration helper
       (write tracker). This manual page describes the ploop user space tool  which  is  used  to
       perform various operations related to ploop devices and images.

       Note  that  this  ploop  tool  is  not  aware  of  container  entities. Commands that have
       DiskDescriptor.xml as an argument work with an XML  file  that  contains  meta-information
       about  a  particular ploop device configuration: device characteristics (block size etc.),
       storage  information  (names  and  formats  of  images  used  for  the  device),  snapshot
       information,  etc.  If  a  particular  command  can  be  used  both  with  and without the
       DiskDescriptor.xml  argument,  it   is   strongly   advised   to   use   the   form   with
       DiskDescriptor.xml.

OPTIONS

Run ploop without any options to show a short synopsss, including a list of commands.

Run ploop command to show synopsis and a short description for a particular command.

Basic commands

init

Create and initialize a ploop image file and a corresponding DiskDescriptor.xml file.

ploop init -s size [-f format] [-v version] [-t fstype] [-b blocksize] [-B fsblocksize]
[--nolazy] delta_file

-s size Image size. If no suffix is specified, the size is in sector units (one sector
is 512 bytes). One can specify optional K, M, G or T suffix to set the size in
kilo-, mega-, giga- or terabytes.

-f format Image format. See Image formats below.

-v version Image version, can be 1 or 2. Default is 2, if supported by the kernel.

-t none|ext3|ext4
File system type to create, default is ext4. Unless none is specified, a
partition, a filesystem, and a balloon file will be created inside the image.
Using ext3 is not recommended.

-b blocksize
Device block size, in 512 byte sectors. Default block size is 2048 sectors, or
1 megabyte.

-B fsblocksize
Filesystem block size, in bytes. Default is 4096 bytes.

-n, --nolazy
Disable lazy mkfs initialization (which is enabled by default). Currently that
means if this flag is set, mkfs.ext4(8) is called with
-Elazy_itable_init=0,lazy_journal_init=0 options.

delta_file Path to a non-existent image file to be created.

mount

Assemble a ploop device from one or more delta images, start it, and optionally mount the
file system residing on the device.

Two forms of this command are provided. The first one accepts a list of delta images to be
used for assembling the ploop device, while the second one is using information from a
DiskDescriptor.xml file. Please note that not all mount options are applicable to both
forms.

ploop mount [-r] [-F] [-f format] [-b blocksize] [-d device] [-m mount_point]
[-o mount_options] [-t fstype] base_delta [... top_delta]

ploop mount [-r] [-F] [-d device] [-m mount_point] [-o mount_options] [-t fstype]
[-u uuid] DiskDescriptor.xml

-r Mount as read-only.

-F Run fsck(8) on inner filesystem before mounting it. This option is ignored if
-m is not used.

-f format Image format. Ignored if DiskDescriptor.xml is specified. Otherwise, one need
to specify raw as an argument, if raw image format is used.

-b blocksize
Device block size, in 512 byte sectors. Ignored if DiskDescriptor.xml is
specified. Otherwise, required for raw images.

-d device Ploop device to use, e.g. /dev/ploop0. If not specified, a randomly numbered
ploop device will be used.

-m mount_point
If this option is specified, ploop goes on to mount the file system to
directory denoted by mount_point.

-o mount_options
Any additional mount options, comma-separated. Used if -m is set.

-t fstype File system type used for mounting. Used if -m is set. The default is ext4.

-u uuid | base
GUID of the image from the DiskDescriptor.xml to be mounted. By default, top
GUID is used. The special 'base' value can be used to mount the base (lower-
level) image.

base_delta [... top_delta]
List of image files to mount, with the first one being the base delta and the
last one being the top delta (i.e. the one that will be writable unless -r is
specified).

DiskDescriptor.xml
Path to the DiskDescriptor.xml file with information about images.

umount

Unmount a ploop device. Since a mounted ploop device consists of an image (or multiple
images), a device, and (optionally) a file system mounted to a directory, one can refer to
any of the above entities to specify what to unmount. The recommended way is to use
DiskDescriptor.xml.

ploop umount { -d device | -m mount_point | DiskDescriptor.xml | image_file }

-d device Ploop device, e.g., /dev/ploop0.

-m mount_point
Mount point of a ploop device to unmount.

DiskDescriptor.xml
Path to the DiskDescriptor.xml file with information about images.

image_file Path to a mounted image file.

replace

Replaces a ploop image by a different (but identical) one, on a running ploop device. Only
a read-only image (e.g. a non-top one in a stacked configuration) can be replaced. An
image to be replaced is specified by either one of level, UUID, or the current image file.

If a new image is not identical to the old one (i.e. its content differs) or not suitable
for ploop in any other way (e.g. it is sparse, or resides on a file system not supported
by ploop), the result is undefined.

ploop replace { -u uuid | -l level | -o cur_image_file } [--keep-name] -i image_file
DiskDescriptor.xml

-u uuid A uuid of an image to be replaced.

-l level A level of image to be replaced. A level is a distance of an image from the
base delta.

-o cur_image_file
A current image file (the one to replace).

-k, --keep-name
A flag to keep the same image file name. If this flag is set, after the
image is replaced, a new image_file is renamed to the old one (removing the
old, now unused, image), so no modification to DiskDescriptor.xml is
required.

-i image_file A new replacement image.

DiskDescriptor.xml
Path to the DiskDescriptor.xml file with information about images.

resize

Resize a ploop image. Both online (i.e. when ploop is mounted and used) and offline resize
is supported, and the tool can either grow or shrink both the ploop image and the
underlying file system.

ploop resize -s size DiskDescriptor.xml

-s size Image size. If no suffix is specified, size is in sector units (one sector is
512 bytes). One can specify optional K, M, G or T suffix to set the size in
kilo-, mega-, giga- or terabytes.

DiskDescriptor.xml
Path to the DiskDescriptor.xml file with information about images.

convert

Convert either ploop image format or version (but not both at the same time). Conversion
can only be performed offline (i.e. image should not be in use).

ploop convert { -f format | -v version } DiskDescriptor.xml

-f format Image format. See Image formats below.

-v version Image version, can be 1 or 2.

check

Check the internal consistency of (and possibly repair) a ploop image (or images). Note
that image(s) to be tested should not be in use.

ploop check [-u uuid] DiskDescriptor.xml

Check all the images in DiskDescriptor.xml up to the one denoted by the uuid (or default
top delta, if UUID is not specified). Default built-in check options are used, and the
ones specified on the command line, if any, are ignored.

ploop check [--force] [--hard-force] [--check] [--ro] [--silent] [--drop-inuse] [--raw]
[--blocksize size] [--repair-sparse] DiskDescriptor.xml | image_file

-f, --force Force check even if image's dirty flag is not set.

-F, --hard-force
Same as -f, plus try to fix even fatal errors (can be dangerous).

-c, --check Check for duplicated blocks and holes.

-r, --ro Read-only access, do not modify image(s).

-s, --silent
Be more silent, only report errors.

-d, --drop-inuse
Drop image "in use" flag.

-R, --raw Specifies that image_file is a raw ploop image.

-b, --blocksize size
Image cluster block size, in sectors (for raw images).

-S, --repair-sparse
Repair sparse image(s).

Miscellaneous commands

info

ploop info DiskDescriptor.xml
When run without any options, show information about disk space and inodes usage and
limits on the inner ploop filesystem, somewhat similar to vzquota(8) stat or show
commands.

ploop info [-s] [-d] DiskDescriptor.xml
Either one or both options can be used together. Option -s is used to show information
about ploop device size, block size, and format version. Option -d is used to show a
corresponding ploop block device, it available. file.

list

ploop list [-a]

Shows a list of running ploop devices (first column) and their corresponding base images.
With option -a it also shows a mount point (third column).

restore-descriptor

Create DiskDescriptor.xml file suitable for delta_file and put it into disk_dir.

ploop restore-descriptor -f format [-b blocksize] disk_dir delta_file

Read image header in case of ploop1 format or check raw image size and generate proper
DiskDescriptor.xml file. You can specify blocksize for raw images. If it's not specified
it will be chosen automatically - largest possible value between 32K and 1M. Raw image
size must be aligned to blocksize.

This command works only for base images. Snapshots are not supported.

Working with snapshots
Ploop snapshots is a mechanism for creating and managing instant states of a running file
system. Creating a snapshot leads to creating a new empty ploop image which is layered on
top of an old one, then all writes are ending up in the top image, and reads are falling
through to a lower level. There can be up to 126) stacked ploop images (or snapshots).
Online snapshot merging is also supported.

Snapshots are identified by a unique UUID. A snapshot can be mounted using ploop mount -u
uuid command, see above.

snapshot

Create a ploop snapshot.

ploop snapshot [-u uuid] DiskDescriptor.xml

-u uuid Specify a uuid for a new snapshot. If option is not given, uuid is
generated automatically. To generate uuid manually, one can use the
uuidgen(1) utility. Note that UUID must be enclosed in curly brackets.

snapshot-merge

Merge a snapshot with its parent. That is, contents of the delta file corresponding to the
snapshot is merged to a parent delta, then the file is removed. Parent snapshot UUID is
lost (as it is replaced with the uuid specified). All snapshots having the lost one as a
parent are updated to have the uuid as its parent.

ploop snapshot-merge [-u uuid [-U uuid2] | -A] [-n new_delta] DiskDescriptor.xml

-u uuid Specify a single snapshot uuid to merge. If this option is not
specified, the top delta will be used.

-U uuid2 Together with -u uuid, specify that all snapshots in the range
uuid...uuid2 are to be merged.

-A Merge all snapshots down to base delta. If some snapshots have more
than a single child, they will be impossible to merge.

-n new_delta If this option is set, instead of merging the child delta into its
parent, both the parent and the child deltas are merged into a newly
created file new_delta, which replaces the parent delta. Both deltas
are then removed.

snapshot-switch

Switch to the specified snapshot. This operation can only be performed while ploop is not
running (i.e. is unmounted). The current top delta image will be removed.

ploop snapshot-switch -u uuid DiskDescriptor.xml

-u uuid Specify a snapshot uuid to switch to.

snapshot-delete

Delete the specified snapshot. This operation can only be performed if the specified
snapshot is not active. In case snapshot doesn't have any children, it will simply be
removed. In case snapshot has a single child, it will be merged to that child. Deleting a
snapshot that has multiple children is currently not supported (but can be performed
manually in an iterative fashion).

ploop snapshot-delete -u uuid DiskDescriptor.xml

-u uuid Specify a snapshot uuid to be deleted.

snapshot-list

List available snapshots.

ploop snapshot-list [-H] [-u uuid] [-s] [-o field[,field...]] DiskDescriptor.xml

-H, --no-header Suppress displaying the header row. Usable for scripts.

-u, --uuid, --id uuid
Filter the output to a specified uuid.

-s, --snapshot List in terms of snapshots. By default (i.e. without this option) the
command lists all deltas, and top delta is marked as current. When
this option is used, top delta is not listed, and the snapshot which
is the parent of top delta is marked as current.

-o, --output field[,field...]
Display only the specified fields. Possible fields are:
• uuid - snapshot's UUID;
• parent_uuid - snapshot's parent UUID;
• current - if this snapshot is the current one;
• fname - snapshot image file name.

Image copying
ploop copy is a mechanism of effective copying of a top ploop image with the help of
build-in ploop kernel driver feature called write tracker. Write tracker is a feature
that lets ploop copy to iteratively obtain a list of modified image blocks from the
kernel. Two ploop copy processes are required for iterative top delta transfer. These are
used by vzmigrate(8).

copy (sending)

ploop copy -s device [-F stop_command] { [-d file] | [-o output_fd] [-f feedback_fd] }

This command enables the in-kernel write tracker for the specified ploop device, then
sends all the data blocks from the top delta image to a pipe specified by the output_fd
argument (stdout, i.e. 1 by default), supposedly read by destination ploop copy, or a
file. After that, it iteratively gets the list of the modified data blocks from the
kernel and sends those blocks again. After a number of iterations (or when the list is
empty), it executes the stop_command (this could be vzctl stop or vzctl chkpnt) and does
the last iteration of sending the modified data blocks. Finally, it checks that the data
were not modified, error is returned otherwise.

If feedback_fd is specified, it is used to read back from the ploop copy receiving side.
The feedback channel is currently used to wait for fdatasync(2) completion.

copy (receiving)

ploop copy -d file [-i input_fd] [-f feedback_fd]

Reads the data blocks (provided by the source ploop copy) from the file descriptor
input_fd (stdin, i.e. 0 by default) and writes them to the file.

If feedback_fd is specified, it is used to send status back to the ploop copy sending
side.

Ballooning
Since there is no online shrink support in ext4 file system, ploop internally uses a
technique called "ballooning" as a work around to shrink its images.

Ballooning operation consists of inflating a special balloon file (invisible for ordinary
users), loading fiemap info of the inflated balloon to the kernel, relocating blocks of
the image file from the tail to the space specified by fiemap info, and truncating the
tail of the image file. Result is the image file of a smaller size.

However, it is quite possible that inflated balloon file will only span blocks that were
never touched before. Those will look like "not allocated" space from the kernel ploop
point of view. In this case nothing will be relocated and nothing truncated.

So, if balloon operation succeeded, it's only guaranteed that a user of ploop device won't
be able to consume more space than the initial block device size minus the size of the
inflated balloon. On the other hand, if a user of block device used a lot of space on it,
then freed the significant part of used space, balloon operation will result in
significant truncate of image file.

All the ploop ballooning logic is hidden from the end user, so while a number of low-level
commands exist for working with ploop ballooning, those are not needed and therefore are
not documented here, except for a single command.

balloon discard

In a situation when a lot of disk space were freed on an in-ploop filesystem, use ploop
balloon discard to optimize the ploop image size.

ploop balloon discard [--automount] [--to-free size] [--min-block min_size] [--defrag]
DiskDescriptor.xml

Iteratively try to relocate and discard unused blocks from a ploop image, reducing its
size.

Note that ploop device and its inner file system should be mounted. If not, one can use
--automount option to automatically mount ploop for the duration of the operation.

Option --defrag can be used to run a filesystem defragmentation utility (currently
e4defrag2 on ext4 only) before the main operation.

Option --to-free can be used to specify a maximum disk space to be freed. In other words,
stop the process once freed space exceeded requested size. Default is 0, meaning to try to
free as much space as possible.

Option --min-block can be used to specify a minimum size of an extent to free. The
smallest possible extent is 1 cluster (currently 1 MB), one can specify higher value to
speed up the whole discarding operation.

Note that the same functionality is available by means of vzctl compact command.

Image formats
The following image formats are currently supported.

raw Raw format, with 1:1 mapping between the image file and the ploop device.

ploop1, expanded
Expanded format. The image will grow according to the needs of the underlying file
system. This format is the default. Names 'ploop1' and 'expanded' are aliases.

preallocated
This is the same as 'ploop1' or 'expanded', the only difference is all the file
blocks are allocated during creation.

EXIT STATUS

       ploop exits with status 0 in case of successful  execution.  Any  status  greater  than  0
       signifies an error.

       1, SYSEXIT_CREAT
              Error creating a file.

       2, SYSEXIT_DEVICE
              Error getting or opening a ploop device.

       3, SYSEXIT_DEVIOC
              Error doing ioctl(2) on ploop device.

       4, SYSEXIT_OPEN
              Error opening a file.

       5, SYSEXIT_MALLOC
              Not    enough   memory   (error   from   malloc(3),   realloc(3),   calloc(3),   or
              posix_memalign(3)).

       6, SYSEXIT_READ
              Error during read.

       7, SYSEXIT_WRITE
              Error during write.

       9, SYSEXIT_SYSFS
              Error reading from a sysfs file (usually under /sys/block/ploop...).

       11, SYSEXIT_PLOOPFMT
              Corrupted ploop image detected.

       12, SYSEXIT_SYS
              Other system error.

       13, SYSEXIT_PROTOCOL
              Broken protocol (unexpected value received).

       14, SYSEXIT_LOOP
              pcopy command can't finalize copying (frozen filesystem is changing).

       15, SYSEXIT_FSTAT
              Error from stat(2), fstat(2), or statfs(2).

       16, SYSEXIT_FSYNC
              Error from fsync(2) or syncfs(2).

       17, SYSEXIT_EBUSY
              Can't continue, another operation is in progress.

       18, SYSEXIT_FLOCK
              Error from flock(2).

       19, SYSEXIT_FTRUNCATE
              Error from ftruncate(2) or truncate(2).

       20, SYSEXIT_FALLOCATE
              Error from fallocate(2).

       21, SYSEXIT_MOUNT
              Can't mount ploop image or file system.

       22, SYSEXIT_UMOUNT
              Can't unmount ploop image or file system.

       23, SYSEXIT_LOCK
              Locking failed (another operation in progress?).

       24, SYSEXIT_MKFS
              Can't create file system.

       26, SYSEXIT_RESIZE_FS
              Utility resizefs failed.

       27, SYSEXIT_MKDIR
              Error from mkdir(2).

       28, SYSEXIT_RENAME
              Error from rename(2).

       29, SYSEXIT_ABORT
              Operation aborted.

       30, SYSEXIT_RELOC
              Block relocation failed.

       33, SYSEXIT_CHANGE_GPT
              Error resizing GPT partition table.

       35, SYSEXIT_UNLINK
              Error from unlink(2).

       36, SYSEXIT_MKNOD
              Error from mknod(2).

       37, SYSEXIT_PLOOPINUSE
              Image is already in use.

       38, SYSEXIT_PARAM
              Invalid parameter.

       39, SYSEXIT_DISKDESCR
              Problem with DiskDescriptor.xml file.

       40, SYSEXIT_DEV_NOT_MOUNTED
              Ploop image is not mounted.

       41, SYSEXIT_FSCK
              Error from fsck(8).

       43, SYSEXIT_NOSNAP
              Can't find specified snapshot UUID.

NAME

SYNOPSIS

DESCRIPTION

OPTIONS

EXIT STATUS

SEE ALSO