Provided by: simplesnap_1.0.4+nmu1_all bug


       simplesnap - Simple and powerful way to send ZFS snapshots across a    network


       simplesnap  [  --sshcmd  COMMAND  ]  [  --wrapcmd  COMMAND ] [ --local ] [ --backupdataset
        [ --datasetdest DEST ] ] --store STORE --setname NAME --host HOST

       simplesnap --check TIMEFRAME --store STORE --setname NAME [ --host HOST ]


       simplesnap is a simple way to send ZFS snapshots across a network.  Although it can  serve
       many  purposes,  its primary goal is to manage backups from one ZFS filesystem to a backup
       filesystem also running ZFS, using incremental backups to  minimize  network  traffic  and
       disk usage.

       simplesnap  is  FLEXIBLE;  it  is  designed  to  perfectly  compliment snapshotting tools,
       permitting rotating backups with arbitrary retention periods.  It lets  multiple  machines
       back  up  a  single  target,  lets  one machine back up multiple targets, and keeps it all

       simplesnap is EASY; there is no configuration file needed.  One ZFS property is  available
       to  exclude  datasets/filesystems.   ZFS datasets are automatically discovered on machines
       being backed up.

       simplesnap is SAFE; it is robust in the face of interrupted transfers,  and  needs  little
       help to keep running.

       simplesnap  is  SECURE; unlike many similar tools, it does not require full root access to
       the machines being backed up.  It runs only a small wrapper as root, and the  wrapper  has
       only three commands it implements.

       Besides the above, simplesnap:

       · Does one thing and does it well.  It is designed to be used with a snapshot auto-rotator
         on both ends (such as zfSnap).  simplesnap will transfer snapshots made by other  tools,
         but will not destroy them on either end.

       · Requires  ssh public key authorization to the host being backed up, but does not require
         permission to run arbitrary commands.  It has a wrapper  to  run  on  the  backup  host,
         written  in  bash,  which accepts only three operations and performs them simply.  It is
         suitable for a locked-down authorized_keys file.

       · Creates minimal snapshots for its own internal purposes, generally leaving no more  than
         1 or 2 per dataset, and reaps them automatically without touching others.

       · Is  a  small  program,  easily audited.  In fact, most of the code is devoted to sanity-
         checking, security, and error checking.

       · Automatically discovers what datasets to back up from the remote.  Uses  a  user-defined
         zfs property to exclude filesystems that should not be backed up.

       · Logs copiously to syslog on all hosts involved in backups.

       · Intelligently  supports  a  single  machine being backed up by multiple backup hosts, or
         onto multiple sets of backup media (when, for instance,  backup  media  is  cycled  into
         offsite storage)

       simplesnap's operation is very simple.

       The  simplesnap  program  runs on the machine that stores the backups -- we'll call it the
       backuphost.  There is a restricted remote command wrapper called simplesnapwrap that  runs
       on  the  machine being backed up -- we'll call it the activehost.  simplesnapwrap is never
       invoked directly by the end-user; it is always called remotely by simplesnap.

       With simplesnap, the backuphost always connects to the activehost -- never the  other  way

       simplesnap  runs  in  the  backuphost,  and  first  connects  to the simplesnapwrap on the
       activehost  and  asks  it  for  a  list  of  the  ZFS   datasets   ("listfs"   operation).
       simplesnapwrap  responds  with  a  list  of  all  ZFS  datasets  that were not flagged for

       Next, simplesnap connects back to simplesnapwrap once for each dataset to be backed up  --
       the  "sendback" operation.  simplesnap passes along to it only two things: the setname and
       the dataset (filesystem) name.

       simplesnapwrap looks to see if there is an existing simplesnap snapshot  corresponding  to
       that  SETNAME.   If  not,  it  creates one and sends it as a full, non-incremental backup.
       That completes the job for that dataset.

       If there is an existing snapshot for that  SETNAME,  simplesnapwrap  creates  a  new  one,
       constructing  the  snapshot  name  containing  a  timestamp and the SETNAME, then sends an
       incremental, using the oldest snapshot from that setname as the basis for zfs send -I.

       After the  backuphost  has  observed  zfs  receive  exiting  without  error,  it  contacts
       simplesnapwrap  once  more  and  requests  the  "reap"  operation.  This cleans up the old
       snapshots for the given SETNAME, leaving  only  the  most  recent.   This  is  a  separate
       operation  in  simplesnapwrap ensuring that even if the transmission is interrupted, still
       it will be OK in the end because zfs receive -F is used, and the  data  will  come  across
       next time.

       The  idea  is  that  some  system  like  zfSnap will be used on both ends to make periodic
       snapshots and clean them up.  One  can  use  careful  prefix  names  with  zfSnap  to  use
       different  prefixes on each activehost, and then implement custom cleanup rules with -F on
       the holderhost.


       This section will describe how a  first-time  simplesnap  user  can  get  up  and  running
       quickly.  It assumes you already have simplesnap installed and working on your system.  If
       not, please follow the instructions in the INSTALL.txt file in the source distribution.

       As above, I will refer to the machine storing the backups  as  the  "backuphost"  and  the
       machine being backed up as the "activehost".

       First,  on  the backuphost, as root, generate an ssh keypair that will be used exclusively
       for simplesnap.

       ssh-keygen -t rsa -f ~/.ssh/id_rsa_simplesnap

       When prompted for a passphrase, leave it empty.

       Now, on the activehost, edit or create a file called  ~/.ssh/authorized_keys.   Initialize
       it  with the content of ~/.ssh/ from the backuphost.  (Or, add to the
       end, if you already have lines in the file.)  Then, at the beginning of that one very long
       line, add text like this:


       (I broke that line into two for readability, but this must all be on a single line in your

       The is the IP address that connections from the backuphost  will  appear  to  come
       from.   It may be omitted if the IP is not static, but it affords a little extra security.
       The line will wind up looking like:

       no-port-forwarding,no-X11-forwarding,no-pty ssh-rsa AAAA....

       (Again, this should all be on one huge line.)

       If  there  are  any  ZFS   datasets   you   do   not   want   to   be   backed   up,   set
       org.complete.simplesnap:exclude property on the activehost to on.  For instance:

       zfs set org.complete.simplesnap:exclude=on tank/junkdata

       Now, back on the backuphost, you should be able to run:

       ssh -i ~/.ssh/id_rsa_simplesnap activehost

       say yes when asked if you want to add the key to the known_hosts file.  At this point, you
       should see output containing:

       "simplesnapwrap: This program is to be run from ssh."

       If you see that, then simplesnapwrap was properly invoked remotely.

       Now, create a ZFS filesystem to hold your backups.  For instance:

       zfs create tank/simplesnap

       I often recommend compression for simplesnap datasets, so:

       zfs set compression=lz4 tank/simplesnap

       (If that gives an error, use compression=on instead.)

       Now, you can run the backup:

       simplesnap --host activehost --setname mainset --store tank/simplesnap  --sshcmd  "ssh  -i

       You  can  monitor progress in /var/log/syslog.  If all goes well, you will see filesystems
       start to be populated under tank/simplesnap/host.


       Now, go test that you have the data you expected to: look at your  STORE  filesystems  and
       make  sure  they have everything expected.  Test repeatedly over time that you can restore
       as you expect from your backups.


       Most people will always use the same SETNAME.  The SETNAME is used to track and  name  the
       snapshots on the remote end.  simplesnap tries to always leave one snapshot on the remote,
       to serve as the base for a future incremental.

       In some situations, you may  have  multiple  bases  for  incrementals.   The  two  primary
       examples  are two different backup servers backing up the same machine, or having two sets
       of backup media and rotating them to offsite storage.  In these situations, you will  have
       to  keep  different snapshots on the activehost for the different backups, since they will
       be current to different points in time.


       All simplesnap options begin with two dashes (`--').  Most take a parameter, which  is  to
       be  separated  from  the  option by a space.  The equals sign is not a valid separator for

       The normal simplesnap mode is backing up.  An alternative check mode is  available,  which
       requires fewer parameters.  This mode is described below.

       --backupdataset DATASET
              Normally,  simplesnap  automatically obtains a list of datasets to back up from the
              remote,   and   backs   up   all   of   them   except   those   that   define   the
              org.complete.simplesnap:exclude=on property.  With this option, simplesnap does not
              bother to ask the remote for a list of datasets, and instead backs up only the  one
              precise DATASET given.  For now, ignored when --check is given, but that may change
              in the future.  It would be best to not specify this option with --check for now.

       --check TIMEFRAME
              Do not back up, but check existing backups.  If  any  datasets'  newest  backup  is
              older than TIMEFRAME, print an error and exit with a nonzero code.  Scans all hosts
              unless a specific host is given with --host.  The parameter is in the format  given
              to  GNU  date(1);  for  instance, --check "30 days ago".  Remember to enclose it in
              quotes if it contains spaces.

       --datasetdest DEST
              Valid only with --backupdataset, gives a specific destination for the backup, whith
              may  be  outside  the STORE.  The STORE must still exist, as it is used for storing
              lockfiles and such.

       --host HOST
              Gives the name of the host to back up.  This is both passed to ssh and used to name
              the backup sets.

              In  a  few  situations,  one  may  not  wish  to use the same name for both.  It is
              recommend to use the Host  and  HostName  options  in  ~/.ssh/config  to  configure
              aliases in this situation.

              Specifies that the host being backed up is local to the machine.  Do not use ssh to
              contact it, and invoke the wrapper directly.  You would not need to  give  --sshcmd
              in  this  case.   For instance: simplesnap --local --store /bakfs/simplesnap --host
              server1 --setname bak1

       --sshcmd COMMAND
              Gives the command to use to connect to the remote host.  Defaults to "ssh".  It may
              be  used to select an alternative configuration file or keypair.  Remember to quote
              it  per  your  shell  if  it  contains  spaces.   For  example:  --sshcmd  "ssh  -i
              /root/.id_rsa_simplesnap".   This  command  is  ignored  when --local or --check is

       --setname SETNAME
              Gives the backup set name.  Can just be a made-up word if  multiple  sets  are  not
              needed;  for  instance, the hostname of the backup server.  This is used as part of
              the snapshot name.

       --store STORE
              Gives the ZFS dataset name where the data will be stored.  Should not begin with  a
              slash.  The mountpoint will be obtained from the ZFS subsystem.  Always required.

       --wrapcmd COMMAND
              Gives  the  path  to  simplesnapwrap  (which  must  be on the remote machine unless
              --local  is  given).   Not  usually  relevant,  since  the  command  parameter   in
              ~root/.ssh/authorized_keys gives the path.  Default: "simplesnapwrap"


       Since  simplesnap  stores backups in standard ZFS datasets, you can use standard ZFS tools
       to obtain information about backups.  Here are some examples.

       Try something like this:

       # zfs list -r -d 1 tank/store
       NAME               USED  AVAIL  REFER  MOUNTPOINT
       tank/store         540G   867G    34K  /tank/store
       tank/store/host1   473G   867G    32K  /tank/store/host1
       tank/store/host2  54.9G   867G    32K  /tank/store/host2
       tank/store/host3  12.2G   867G    31K  /tank/store/host3

       Here, you can see that the total size of the simplesnap data is 540G - the USED value from
       the  top  level.  In this example, host1 was using the most space -- 473G -- and host3 the
       least -- 12.2G.  There is 867G available on this zpool for backups.

       The -r parameter to zfs list requests a recursive report, but the -d 1  parameter  sets  a
       maximum  depth of 1 -- so you can see just the top-level hosts without all their component

       Let's say that you had the above example,  and  want  to  drill  down  into  more  detail.
       Perhaps, for instance, we continue the above example and drill down into host2:

       # zfs list -r tank/store/host2
       NAME                                 USED  AVAIL  REFER  MOUNTPOINT
       tank/store/host2                    54.9G   867G    32K  /tank/...
       tank/store/host2/tank               49.8G   867G    32K  /tank/...
       tank/store/host2/tank/home          7.39G   867G  6.93G  /tank/...
       tank/store/host2/tank/vm            42.4G   867G    30K  /tank/...
       tank/store/host2/tank/vm/vm1        32.0G   867G  29.7G  -
       tank/store/host2/tank/vm/vm2        10.4G   867G  10.4G  -
       tank/store/host2/rpool              5.12G   867G    32K  /tank/...
       tank/store/host2/rpool/misc          521M   867G   521M  /tank/...
       tank/store/host2/rpool/host2-1      4.61G   867G    33K  /tank/...
       tank/store/host2/rpool/host2-1/ROOT  317M   867G   312M  /tank/...
       tank/store/host2/rpool/host2-1/usr  3.76G   867G  3.76G  /tank/...
       tank/store/host2/rpool/host2-1/var   554M   867G   401M  /tank/...

       I've trimmed the "mountpoint" column here so it doesn't get too wide for the screen.

       You  see  here  the  same  54.9G used as in the previous example, but now you can trace it
       down.  There were two zpools on host2: tank and rpool.  Most of the backup space --  49.8G
       of  the  54.9G -- is used by tank, and only 5.12G by rpool.  And in tank, 42.4G is used by
       vm.  Tracing it down, of that 42.4G used by vm, 32G is in vm1 and 10.4G  in  vm2.   Notice
       how the values at each level of the tree include their descendents.

       So  in  this example, vm1 and vm2 are zvols corresponding to virtual machines, and clearly
       take up a lot of space.  Notice how vm1 says it uses 32.0G but in  the  refer  column,  it
       only  refers to 29.7G?  That means that the latest backup for vm2 used 29.7G, but when you
       add in the snapshots for that dataset, the total space consumed is 32.0G.

       Let's look at an alternative view that will make  the  size  consumed  by  snapshots  more

       # zfs list -o space -r tank/store/host2
       NAME                         AVAIL   USED  USEDSNAP  USEDDS  USEDCHILD
       .../host2                     867G  54.9G         0     32K      54.9G
       .../host2/tank                867G  49.8G         0     32K      49.8G
       .../host2/tank/home           867G  7.39G      474M   6.93G          0
       .../host2/tank/vm             867G  42.4G       50K     30K      42.4G
       .../host2/tank/vm/vm1         867G  32.0G     2.35G   29.7G          0
       .../host2/tank/vm/vm1         867G  10.4G       49K   10.4G          0
       .../host2/rpool               867G  5.12G         0     32K      5.12G
       .../host2/rpool/misc          867G   521M       51K    521M          0
       .../host2/rpool/host2-1       867G  4.61G       51K     33K      4.61G
       .../host2/rpool/host2-1/ROOT  867G   317M     5.44M    312M          0
       .../host2/rpool/host2-1/usr   867G  3.76G      208K   3.76G          0
       .../host2/rpool/host2-1/var   867G   554M      153M    401M          0

       (Again, I've trimmed some irrelevant columns from this output.)

       The  AVAIL  and  USED columns are the same as before, but now you have a breakdown of what
       makes up the USED column.  USEDSNAP is the space used by the snapshots of that  particular
       dataset.   USEDDS  is  the space used by that dataset directly -- the same value as was in
       REFER before.  And USEDCHILD is the space used by descendents of that dataset.

       The USEDSNAP column is the easiest way to see the impact your retention policies  have  on
       your backup space consumption.

       Let's  take  one example from before -- the 153M of snapshots in host2-1/var, and see what
       we can find.

       # zfs list -t snap -r tank/store/host2/rpool/host2-1/var
       NAME                                              USED  AVAIL  REFER
       .../var@host2-hourly-2014-02-11_05.17.02--2d       76K      -   402M
       .../var@host2-hourly-2014-02-11_06.17.01--2d       77K      -   402M
       .../var@host2-hourly-2014-02-11_07.17.01--2d     18.8M      -   402M
       .../var@host2-daily-2014-02-11_07.17.25--1w        79K      -   402M
       .../var@host2-hourly-2014-02-11_08.17.01--2d      156K      -   402M
       .../var@host2-monthly-2014-02-11_09.01.36--1m     114K      -   402M

       In this output, the REFER column is the amount of data pointed to by that snapshot -- that
       is,  the  size  of  /var  at  the moment the snapshot is made.  And the USED column is the
       amount of space that would be freed if just that snapshot were deleted.

       Note this important point: it is normal for the sum of the values in the USED column to be
       less  than  the space consumed by the snapshots of the datasets as reported by USEDSNAP in
       the previous example.  The reason is that the USED column is the data unique to  that  one
       snapshot.  If, for instance, 100MB of data existed on the system being backed up for three
       hours yesterday, each snapshot could very well show less than  100KB  used,  because  that
       100MB  isn't  unique to a particular snapshot.  Until, that is, two of the three snapshots
       referncing the 100MB data are destroyed; then the USED value of the last  one  referencing
       it will suddenly jump to 100MB higher because now it references unique data.

       One  other point -- an indication that the last backup was successfully transmitted is the
       presence of a __simplesnap_...__ snapshot at the end of the list.  Do not delete it.

       The zfs diff command can let you see what changed over time  --  either  across  a  single
       snapshot, or across many.  Let's take a look.

       # zfs diff .../var@host2-hourly-2014-02-11_05.17.02--2d \
         .../var@host2-hourly-2014-02-11_06.17.01--2d \
         | sort -k2 | less
       M    /tank/store/host2/rpool/host2-1/var/log/Xorg.0.log
       M    /tank/store/host2/rpool/host2-1/var/log/auth.log
       M    /tank/store/host2/rpool/host2-1/var/log/daemon.log
       M    /tank/store/host2/rpool/host2-1/var/spool/anacron/cron.daily
       M    /tank/store/host2/rpool/host2-1/var/spool/anacron/cron.monthly
       M    /tank/store/host2/rpool/host2-1/var/spool/anacron/cron.weekly
       M    /tank/store/host2/rpool/host2-1/var/tmp

       Here  you  can  see why there was just a few KB of changes in that snapshot: mostly just a
       little bit of logging was happening on the system.  Now let's inspect the larger snapshot:

       # zfs diff .../var@host2-hourly-2014-02-11_07.17.01--2d \
          .../var@host2-daily-2014-02-11_07.17.25--1w \
          | sort -k2 | less
       M    /tank/store/host2/rpool/host2-1/var/backups
       +    /tank/store/host2/rpool/host2-1/var/backups/dpkg.status.0
       -    /tank/store/host2/rpool/host2-1/var/backups/dpkg.status.0
       +    /tank/store/host2/rpool/host2-1/var/backups/dpkg.status.1.gz
       R    /tank/store/host2/rpool/host2-1/var/backups/dpkg.status.1.gz -> /tank/store/host2/rpool/host2-1/var/backups/dpkg.status.2.gz
       R    /tank/store/host2/rpool/host2-1/var/backups/dpkg.status.2.gz -> /tank/store/host2/rpool/host2-1/var/backups/dpkg.status.3.gz
       M    /tank/store/host2/rpool/host2-1/var/cache/apt
       R    /tank/store/host2/rpool/host2-1/var/cache/apt/pkgcache.bin.KdsMLu -> /tank/store/host2/rpool/host2-1/var/cache/apt/pkgcache.bin

       Here you can see some file rotation going on,  and  a  temporary  file  being  renamed  to
       permanent.  Normal daily activity on a system, but now you know what was taking up space.


       Any  backup  scheme  should  be  tested  carefully  before  being relied upon to serve its
       intended purpose.  This item is not simplesnap-specific,  but  pertains  to  every  backup
       solution: test that you are backing up the data you expect to before you need it.

       In  order  to account for various situations that could lead to divergence of filesystems,
       including the simple act of mounting them, simplesnap always uses  zfs  receive  -F.   Any
       local  changes you make to the simplesnap store datasets will be lost at any time.  If you
       need to make local changes there, it is best to copy them elsewhere.

       Since simplesnap sends all snapshots, it is possible that locally-created  snapshots  made
       outside  of  your  rotation scheme will also be sent to your backuphost.  These may not be
       automatically reaped there,  and  may  stick  around.   An  example  at  the  end  of  the
       cron.daily.simplesnap.backuphost  file  included  with  simplesnap is one way to check for
       these.  They could automatically be reaped with zfs destroy as  well,  but  this  must  be
       carefully  tuned  to  local requirements, so an example of doign that is intentionally not
       supplied with the distribution.

       simplesnap creates snapshots beginning with __simplesnap_ followed by  your  SETNAME.   Do
       not  create,  remove, or alter these snapshots in any way, either on the activehost or the
       backuphost.   Doing so may lead to unpredictable side-effects.


       Ordinarily, an interrupted transfer is no problem for simplesnap.  However, the very first
       transfer  of a dataset poses a bit of a problem, since the simplesnap wrapper can't detect
       failure in this one special case.  If your first transfer  gets  interrupted,  simply  zfs
       destroy  the  __simplesnap_...__  snapshot  on  the  activehost  and rerun.  NEVER DESTROY

       If, by way of the  org.complete.simplesnap:exclude  property  or  the  --backupdataset  or
       --datasetdest  parameters,  you  do  not  request a parent dataset to be backed up, but do
       request a descendent dataset to be backed up, you may get an error  on  the  first  backup
       because  the dataset tree leading to the destination location for that dataset has not yet
       been created.  simplesnap performs only  the  narrow  actions  you  request.   Running  an
       appropriate zfs create command will rectify the situation.


       zfSnap (1), zfs (8).

       The simplesnap homepage:  <URL:>

       The examples included with the simplesnap distribution, or on its homepage.

       The zfSnap package compliments simplesnap perfectly.  Find it at


       This  software  and  manual  page  was  written  by  John Goerzen <>.
       Permission is granted to copy, distribute and/or modify this document under the  terms  of
       the GNU General Public License, Version 3 any later version published by the Free Software
       Foundation.  The complete text of the GNU General Public License is included in  the  file
       COPYING in the source distribution.

                                         10 October 2017                            SIMPLESNAP(8)