vfs_shadow_copy2 - Expose snapshots to Windows clients as shadow copies.

Author

       The original Samba software and related utilities were created by Andrew Tridgell. Samba is now developed
       by the Samba Team as an Open Source project similar to the way the Linux kernel is developed.

Samba 4.22.3-Ubuntu-4.22.3+dfs                     07/21/2025                                VFS_SHADOW_COPY2(8)

Caveats

       This is not a backup, archival, or version control solution.

       With Samba or Windows servers, vfs_shadow_copy2 is designed to be an end-user tool only. It does not
       replace or enhance your backup and archival solutions and should in no way be considered as such.
       Additionally, if you need version control, implement a version control system.

Configuration

       vfs_shadow_copy2 relies on a filesystem snapshot implementation. Many common filesystems have native
       support for this.

       Filesystem snapshots must be available under specially named directories in order to be recognized by
       vfs_shadow_copy2. These snapshot directory is typically a direct subdirectory of the share root's
       mountpoint but there are other modes that can be configured with the parameters described in detail
       below.

       The snapshot at a given point in time is expected in a subdirectory of the snapshot directory where the
       snapshot's directory is expected to be a formatted version of the snapshot time. The default format which
       can be changed with the shadow:format option is @GMT-YYYY.MM.DD-hh.mm.ss, where:

              •   YYYY is the 4 digit year

              •   MM is the 2 digit month

              •   DD is the 2 digit day

              •   hh is the 2 digit hour

              •   mm is the 2 digit minute

              •   ss is the 2 digit second.

       The vfs_shadow_copy2 snapshot naming convention can be produced with the following date(1) command:

                TZ=GMT date +@GMT-%Y.%m.%d-%H.%M.%S

Description

This VFS module is part of the samba(7) suite.

The vfs_shadow_copy2 VFS module offers a functionality similar to Microsoft Shadow Copy services. When
set up properly, this module allows Microsoft Shadow Copy clients to browse through file system snapshots
as "shadow copies" on Samba shares.

This is a second implementation of a shadow copy module which has the following additional features
(compared to the original shadow_copy(8) module):

1. There is no need any more to populate your share's root directory with symlinks to the
snapshots if the file system stores the snapshots elsewhere. Instead, you can flexibly
configure the module where to look for the file system snapshots. This can be very important
when you have thousands of shares, or use [homes].

2. Snapshot directories need not be in one fixed central place but can be located anywhere in the
directory tree. This mode helps to support file systems that offer snapshotting of particular
subtrees, for example the GPFS independent file sets.

3. Vanity naming for snapshots: snapshots can be named in any format compatible with str[fp]time
conversions.

4. Timestamps can be represented in localtime rather than UTC.

5. The inode number of the files can optionally be altered to be different from the original.
This fixes the 'restore' button in the Windows GUI to work without a sharing violation when
serving from file systems, like GPFS, that return the same device and inode number for the
snapshot file and the original.

6. Shadow copy results are by default sorted before being sent to the client. This is beneficial
for filesystems that don't read directories alphabetically (the default unix). Sort ordering
can be configured and sorting can be turned off completely if the file system sorts its
directory listing.

This module is stackable.

Examples

       Add shadow copy support to user home directories:

                   [homes]vfsobjects=shadow_copy2shadow:snapdir=/data/snapshotsshadow:basedir=/data/homeshadow:sort=desc

Name

       vfs_shadow_copy2 - Expose snapshots to Windows clients as shadow copies.

Options

shadow:mountpoint = MOUNTPOINT
With this parameter, one can specify the mount point of the filesystem that contains the share path.
Usually this mount point is automatically detected. But for some constellations, in particular tests,
it can be convenient to be able to specify it.

Example: shadow:mountpoint = /path/to/filesystem

Default: shadow:mountpoint = NOT SPECIFIED

shadow:snapdir = SNAPDIR
Path to the directory where the file system of the share keeps its snapshots. If an absolute path is
specified, it is used as-is. If a relative path is specified, then it is taken relative to the mount
point of the filesystem of the share root. (See shadow:mountpoint.)

Note that shadow:snapdirseverywhere depends on this parameter and needs a relative path. Setting an
absolute path disables shadow:snapdirseverywhere.

Note that the shadow:crossmountpoints option also requires a relative snapdir. Setting an absolute
path disables shadow:crossmountpoints.

Example: shadow:snapdir = /some/absolute/path

Default: shadow:snapdir = .snapshots

shadow:basedir = BASEDIR
The basedir option allows one to specify a directory between the share's mount point and the share
root, relative to which the file system's snapshots are taken.

For example, if

• basedir = mountpoint/rel_basedir

• share_root = basedir/rel_share_root

• snapshot_path = mountpoint/snapdir

or snapshot_path = snapdir if snapdir is absolute

then the snapshot of a file = mountpoint/rel_basedir/rel_share_root/rel_file at a time TIME will be
found under snapshot_path/FS_GMT_TOKEN(TIME)/rel_share_root/rel_file, where FS_GMT_TOKEN(TIME) is the
timestamp string belonging to TIME in the format required by the file system. (See shadow:format.)

The default for the basedir is the mount point of the file system of the share root (see
shadow:mountpoint).

Note that the shadow:snapdirseverywhere and shadow:crossmountpoints options are incompatible with
shadow:basedir and disable the basedir setting.

shadow:snapsharepath = SNAPSHAREPATH
With this parameter, one can specify the path of the share's root directory in snapshots, relative to
the snapshot's root directory. It is an alternative method to shadow:basedir, allowing greater
control.

For example, if within each snapshot the files of the share have a path/to/share/ prefix, then
shadow:snapsharepath can be set to path/to/share.

With this parameter, it is no longer assumed that a snapshot represents an image of the original file
system or a portion of it. For example, a system could perform backups of only files contained in
shares, and then expose the backup files in a logical structure:

• share1/

• share2/

• .../

Note that the shadow:snapdirseverywhere and the shadow:basedir options are incompatible with
shadow:snapsharepath and disable shadow:snapsharepath setting.

Example: shadow:snapsharepath = path/to/share

Default: shadow:snapsharepath = NOT SPECIFIED

shadow:sort = asc/desc
By default, this module sorts the shadow copy data alphabetically before sending it to the client.
With this parameter, one can specify the sort order. Possible known values are desc (descending, the
default) and asc (ascending). If the file system lists directories alphabetically sorted, one can
turn off sorting in this module by specifying any other value.

Example: shadow:sort = asc

Example: shadow:sort = none

Default: shadow:sort = desc

shadow:localtime = yes/no
This is an optional parameter that indicates whether the snapshot names are in UTC/GMT or in local
time. If it is disabled then UTC/GMT is expected.

shadow:localtime = no

shadow:format = format specification for snapshot names
This is an optional parameter that specifies the format specification for the naming of snapshots in
the file system. The format must be compatible with the conversion specifications recognized by
str[fp]time.

Default: shadow:format = "@GMT-%Y.%m.%d-%H.%M.%S"

shadow:sscanf = yes/no
This parameter can be used to specify that the time in format string is given as an unsigned long
integer (%lu) rather than a time strptime() can parse. The result must be a unix time_t time.

Default: shadow:sscanf = no

shadow:fixinodes = yes/no
If you enable shadow:fixinodes then this module will modify the apparent inode number of files in the
snapshot directories using a hash of the files path. This is needed for snapshot systems where the
snapshots have the same device:inode number as the original files (such as happens with GPFS
snapshots). If you don't set this option then the 'restore' button in the shadow copy UI will fail
with a sharing violation.

Default: shadow:fixinodes = no

shadow:snapdirseverywhere = yes/no
If you enable shadow:snapdirseverywhere then this module will look out for snapshot directories in
the current working directory and all parent directories, stopping at the mount point by default. But
see shadow:crossmountpoints how to change that behaviour.

An example where this is needed are independent filesets in IBM's GPFS, but other filesystems might
support snapshotting only particular subtrees of the filesystem as well.

Note that shadow:snapdirseverywhere depends on shadow:snapdir and needs it to be a relative path.
Setting an absolute snapdir path disables shadow:snapdirseverywhere.

Note that this option is incompatible with the shadow:basedir option and removes the shadow:basedir
setting by itself.

Example: shadow:snapdirseverywhere = yes

Default: shadow:snapdirseverywhere = no

shadow:crossmountpoints = yes/no
This option is effective in the case of shadow:snapdirseverywhere = yes. Setting this option makes
the module not stop at the first mount point encountered when looking for snapdirs, but lets it
search potentially all through the path instead.

An example where this is needed are independent filesets in IBM's GPFS, but other filesystems might
support snapshotting only particular subtrees of the filesystem as well.

Note that shadow:crossmountpoints depends on shadow:snapdir and needs it to be a relative path.
Setting an absolute snapdir path disables shadow:crossmountpoints.

Note that this option is incompatible with the shadow:basedir option and removes the shadow:basedir
setting by itself.

Example: shadow:crossmountpoints = yes

Default: shadow:crossmountpoints = no

shadow:snapprefix
With growing number of snapshots file-systems need some mechanism to differentiate one set of
snapshots from other, e.g. monthly, weekly, manual, special events, etc. Therefore these file-systems
provide different ways to tag snapshots, e.g. provide a configurable way to name snapshots, which is
not just based on time. With only shadow:format it is very difficult to filter these snapshots. With
this optional parameter, one can specify a variable prefix component for names of the snapshot
directories in the file-system. If this parameter is set, together with the shadow:format and
shadow:delimiter parameters it determines the possible names of snapshot directories in the
file-system. The option only supports Basic Regular Expression (BRE).

shadow:delimiter
This optional parameter is used as a delimiter between shadow:snapprefix and shadow:format. This
parameter is used only when shadow:snapprefix is set.

Default: shadow:delimiter = "_GMT"

Synopsis


       vfs objects = shadow_copy2

Version

       This man page is part of version 4.22.3-Ubuntu-4.22.3+dfsg-4ubuntu1 of the Samba suite.