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fssnap_ufs(8)
System Administration Commands fssnap_ufs(8)
NAME
fssnap_ufs - create a temporary snapshot of a UFS file system
SYNOPSIS
fssnap [-F ufs] [-V] -o backing-store=path,
[specific-options] /mount/point
fssnap -d [-F ufs] [-V] /mount/point | dev
fssnap -i [-F ufs] [-V] [-o specific-options] /mount/point | dev
DESCRIPTION
The fssnap command queries, creates, or deletes a temporary snapshot of
a UFS file system. A snapshot is a point-in-time image of a file system
that provides a stable and unchanging device interface for backups.
When creating a file system snapshot, you must specify the file system
to be captured and the backing-store file. The backing-store file(s)
are where the snapshot subsystem saves old file system data before it
is overwritten. Beyond the first backing-store file, fssnap automati‐
cally creates additional backing-store files on an as-needed basis.
The number and size of the backing store files varies with the amount
of activity in the file system. The destination path must have enough
free space to hold the backing-store file(s). This location must be
different from the file system that is being captured in a snapshot.
The backing-store file(s) can reside on any type of file system,
including another UFS file system or an NFS-mounted file system.
OPTIONS
The following options are supported:
-d
Deletes the snapshot associated with the given file system.
-i
Displays the state of one or all UFS snapshots. If a mount-point or
device is not specified, a list of all snapshots on the system is
displayed. When a mount-point or device is specified, detailed
information is provided for the specified file system snapshot by
default.
Use the -o options with the -i option to specify what snapshot
information is displayed. Since this feature is provided primarily
for use in scripts and on the command line, no labels are displayed
for the data. Sizes are all in bytes, and the output is not inter‐
nationalized or localized. The information is displayed on one line
per option. Unrecognized options display a single ? on the line.
One line per option guarantees that there are the same number of
lines as options specified and there is a one-to-one correspondence
between an output line and an option.
The following -o options display specific information for a given
snapshot. See the EXAMPLES section for examples of how to use these
options.
snapnumber
Display the snapshot number.
blockdevname
Display the block device path.
rawdevname
Display the raw device path.
mountpoint
Display the mount point of the master file system.
state
Display the state of the snapshot device.
backing-store
Display the location of the first backing-store file for this
snapshot. If there are multiple backing-store files, subsequent
files have the same name as the first file, with the suffixes
.2, .3, and so forth.
backing-store-len
Display the sum of the sizes of the backing-store files.
maxsize
Display the maxsize value specified for the backing-store
file(s).
createtime
Display the time that the snapshot was created.
chunksize
Display the copy-on-write granularity.
-o specific-options
Without -d or -i, the default action is to create a snapshot. Spec‐
ify the following options when creating a snapshot. All of these
options are discretionary, except for the backing-store file, which
is required.
backing-store=path
Uses path in the creation of the backing-store file(s). path
must not reside on the file system that is being captured in a
snapshot and must not be the name of an existing file. If path
is a directory, then a backing-store file is created within it
using a name that is generated automatically. If path is not a
directory and does not already exist, then a backing-store file
with that name is created. If more than one backing-store file
is required, fssnap creates subsequent files automatically. The
second and subsequent files have the same name as the first
file, with suffixes of .2, .3, and so forth.
This option can be abbreviated as bf=path or bs=path.
unlink
Unlinks the backing-store file after the snapshot is created.
This option specifies that the backing-store file does not need
to be removed manually when the snapshot is deleted. This might
make administration more difficult since the file is not visi‐
ble in the file system. If this option is not specified, the
backing-store files should be removed manually after the snap‐
shot is deleted.
chunksize=n [k,m,g]
Uses n for the chunk size. Chunk size is the granularity of the
data that is sent to the backing store.
Specify chunksize in the following units: k for kilobytes, m
for megabytes, or g for gigabytes. By default, chunk size is
four times the block size of the file system (typically 32k).
maxsize=n[k,m,g]
Does not allow the sum of the sizes of the backing-store
file(s) to exceed n, where n is the unit specified. The snap‐
shot is deleted automatically when the sum of the sizes of the
backing-store file(s) exceeds maxsize.
Specify maxsize in the following units: k for kilobytes, m for
megabytes, or g for gigabytes.
raw
Displays to standard output the name of the raw device instead
of the block device when a snapshot is created. The block
device is printed by default (when raw is not specified). This
option makes it easier to embed fssnap commands in the command
line for commands that require the raw device instead. Both
devices are always created. This option affects only the out‐
put.
OPERANDS
The following operands are supported:
mount-point
The directory where the file system resides.
special
The physical device for the file system, such as /dev/dsk/c0t0d0s7.
EXAMPLES
Example 1 Creating a Snapshot of a File System
The following example creates a snapshot of a file system. The block
special device created for the snapshot is /dev/fssnap/0.
# fssnap -F ufs -o backing-store=/var/tmp /export/home
/dev/fssnap/0
Example 2 Backing Up a File System Snapshot Without Having To Unmount
the File System
The following example backs up a file system snapshot without having to
unmount the file system. Since ufsdump requires the path to a raw
device, the raw option is used. The /export/home file system snapshot
is removed in the second command.
# ufsdump 0uf /dev/rmt/0 `fssnap -F ufs
-o raw,bs=/export/snap /export/home`
<output from ufsdump>
# fssnap -F ufs -d /export/home
Example 3 Backing Up a File System
When backing up a file system, do not let the backing-store file(s)
exceed 400 Mbytes. The second command removes the /export/home file
system snapshot.
# ufsdump 0uf /dev/rmt/0 `fssnap -F ufs
-o maxsize=400m,backing-store=/export/snap,raw
/export/home`
# fssnap -F ufs -d /export/home
Example 4 Performing an Incremental Dump of a Snapshot
The following example uses ufsdump to back up a snapshot of /var. Note
the use of the N option to ufsdump, which writes the name of the device
being dumped, rather than the name of the snapshot device, to
/etc/dumpdates file. See ufsdump(8) for details on the N flag.
# ufsdump lfNu /dev/rmt/0 /dev/rdsk/c0t3d0s2 `fssnap -F ufs
-o raw,bs=/export/scratch,unlink /var`
Example 5 Finding Out What Snapshots Currently Exist
The following command displays the currently existing snapshots.
# fssnap -i
0 /src
1 /export/home
<output continues>
Example 6 Mounting a File System Snapshot
The following example creates a file system snapshot. After you create
a file system snapshot, mount it on /tmp/mount for temporary read-only
access.
# fssnap -F ufs -o backing-store=/nfs/server/scratch /export/home
/dev/fssnap/1
# mkdir /tmp/mount
# mount -F ufs -o ro /dev/fssnap/1 /tmp/mount
Example 7 Creating a File System Snapshot and Unlinking the Backing-
store File
The following example creates a file system snapshot and unlinks the
backing-store file. After creating a file system snapshot and unlinking
the backing-store file, check the state of the snapshot.
# fssnap -o bs=/scratch,unlink /src
/dev/fssnap/0
# fssnap -i /src
Snapshot number : 0
Block Device : /dev/fssnap/0
Raw Device : /dev/rfssnap/0
Mount point : /src
Device state : active
Backing store path : /scratch/snapshot2 <UNLINKED>
Backing store size : 192 KB
Maximum backing store size : Unlimited
Snapshot create time : Sat May 06 10:55:11 2000
Copy-on-write granularity : 32 KB
Example 8 Displaying the Size and Location of the Backing-store File(s)
and the Creation Time for the Snapshot
The following example displays the size of the backing-store file(s) in
bytes, the location of the backing store, and the creation time for the
snapshot of the /test file system.
# fssnap -i -o backing-store-len,backing-store,createtime /test
196608
/snapshot2
Sat May 6 10:55:11 2000
Note that if there are multiple backing-store files stored in /snap‐
shot2, they will have names of the form file (for the first file),
file.1, file.2, and so forth.
EXIT STATUS
The following exit values are returned:
0
Successful completion.
>0
An error occurred.
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ Availabilitysystem/file-system/ufs
The script-readable output mode is a stable interface that can be added
to, but will not change. All other interfaces are subject to change.
SEE ALSO
ntpd(8), mlock(3C), attributes(7)
NOTES
The fssnap device files should be treated like a regular disk block or
character device.
The association between a file system and the snapshot is lost when the
snapshot is deleted or the system reboots. Snapshot persistence across
reboots is not currently supported.
To avoid unnecessary performance impacts, perform the snapshot and sys‐
tem backup when the system is least active.
It is not possible to perform a snapshot of a file system if any of the
following conditions are true:
o The file system is in use by system accounting
o The file system contains a local swap file
o The file system is used as backing store by an application
that uses mlock(3C) to lock its pages. Typically, these are
real time applications, such as ntpd (delivered in the ser‐
vice/network/ntp package).
These conditions result in fssnap being unable to write lock the file
system prior to performing the snapshot.
Oracle Solaris 11.4 19 Dec 2016 fssnap_ufs(8)