mirror of
https://github.com/borgbackup/borg.git
synced 2024-12-24 00:37:56 +00:00
176 lines
6.3 KiB
ReStructuredText
176 lines
6.3 KiB
ReStructuredText
.. include:: ../global.rst.inc
|
||
.. highlight:: none
|
||
|
||
Backing up in pull mode
|
||
=======================
|
||
|
||
Assuming you have a pull backup system set up with borg, where a backup server
|
||
pulls the data from the target via SSHFS. In this mode, the backup client's file
|
||
system is mounted remotely on the backup server. Pull mode is even possible if
|
||
the SSH connection must be established by the client via a remote tunnel. Other
|
||
network file systems like NFS or SMB could be used as well, but SSHFS is very
|
||
simple to set up and probably the most secure one.
|
||
|
||
There are some restrictions caused by SSHFS. For example, unless you define UID
|
||
and GID mappings when mounting via ``sshfs``, owners and groups of the mounted
|
||
file system will probably change, and you may not have access to those files if
|
||
BorgBackup is not run with root privileges.
|
||
|
||
SSHFS is a FUSE file system and uses the SFTP protocol, so there may be also
|
||
other unsupported features that the actual implementations of ssfs, libfuse and
|
||
sftp on the backup server do not support, like file name encodings, ACLs, xattrs
|
||
or bsdflags. So there is no guarantee that you are able to restore a system
|
||
completely in every aspect from such a backup.
|
||
|
||
.. warning::
|
||
|
||
To mount the client's root file system you will need root access to the
|
||
client. This contradicts to the usual threat model of BorgBackup, where
|
||
clients don't need to trust the backup server (data is encrypted). In pull
|
||
mode the server (when logged in as root) could cause unlimited damage to the
|
||
client. Therefore, pull mode should be used only from servers you do fully
|
||
trust!
|
||
|
||
Creating a backup
|
||
-----------------
|
||
|
||
Generally, in a pull backup situation there is no direct way for borg to know
|
||
the client's original UID:GID name mapping of files, because Borg would use
|
||
``/etc/passwd`` and ``/etc/group`` of the backup server to map the names. To
|
||
derive the right names, Borg needs to have access to the client's passwd and
|
||
group files and use them in the backup process.
|
||
|
||
The solution to this problem is chrooting into an sshfs mounted directory. In
|
||
this example the whole client root file system is mounted. We use the
|
||
stand-alone BorgBackup executable and copy it into the mounted file system to
|
||
make Borg available after entering chroot; this can be skipped if Borg is
|
||
already installed on the client.
|
||
|
||
::
|
||
|
||
# Mount client root file system.
|
||
mkdir /tmp/sshfs
|
||
sshfs root@host:/ /tmp/sshfs
|
||
# Mount BorgBackup repository inside it.
|
||
mkdir /tmp/sshfs/borgrepo
|
||
mount --bind /path/to/repo /tmp/sshfs/borgrepo
|
||
# Make borg executable available.
|
||
cp /usr/local/bin/borg /tmp/sshfs/usr/local/bin/borg
|
||
# Mount important system directories and enter chroot.
|
||
cd /tmp/sshfs
|
||
for i in dev proc sys; do mount --bind /$i $i; done
|
||
chroot /tmp/sshfs
|
||
|
||
Now we are on the backup system but inside a chroot with the client's root file
|
||
system. We have a copy of Borg binary in ``/usr/local/bin`` and the repository
|
||
in ``/borgrepo``. Borg will back up the client's user/group names, and we can
|
||
create the backup, retaining the original paths, excluding the repository:
|
||
|
||
::
|
||
|
||
borg create --exclude /borgrepo --files-cache ctime,size /borgrepo::archive /
|
||
|
||
For the sake of simplicity only ``/borgrepo`` is excluded here. You may want to
|
||
set up an exclude file with additional files and folders to be excluded. Also
|
||
note that we have to modify Borg's file change detection behaviour – SSHFS
|
||
cannot guarantee stable inode numbers, so we have to supply the
|
||
``--files-cache`` option.
|
||
|
||
Finally, we need to exit chroot, unmount all the stuff and clean up:
|
||
|
||
::
|
||
|
||
exit # exit chroot
|
||
rm /tmp/sshfs/usr/local/bin/borg
|
||
cd /tmp/sshfs
|
||
for i in dev proc sys borgrepo; do umount ./$i; done
|
||
rmdir borgrepo
|
||
cd ~
|
||
umount /tmp/sshfs
|
||
rmdir /tmp/sshfs
|
||
|
||
Thanks to secuser on IRC for this how-to!
|
||
|
||
Restore methods
|
||
---------------
|
||
|
||
The counterpart of a pull backup is a push restore. Depending on the type of
|
||
restore – full restore or partial restore – there are different methods to make
|
||
sure the correct IDs are restored.
|
||
|
||
Partial restore
|
||
~~~~~~~~~~~~~~~
|
||
|
||
In case of a partial restore, using the archived UIDs/GIDs might lead to wrong
|
||
results if the name-to-ID mapping on the target system has changed compared to
|
||
backup time (might be the case e.g. for a fresh OS install).
|
||
|
||
The workaround again is chrooting into an sshfs mounted directory, so Borg is
|
||
able to map the user/group names of the backup files to the actual IDs on the
|
||
client. This example is similar to the backup above – only the Borg command is
|
||
different:
|
||
|
||
::
|
||
|
||
# Mount client root file system.
|
||
mkdir /tmp/sshfs
|
||
sshfs root@host:/ /tmp/sshfs
|
||
# Mount BorgBackup repository inside it.
|
||
mkdir /tmp/sshfs/borgrepo
|
||
mount --bind /path/to/repo /tmp/sshfs/borgrepo
|
||
# Make borg executable available.
|
||
cp /usr/local/bin/borg /tmp/sshfs/usr/local/bin/borg
|
||
# Mount important system directories and enter chroot.
|
||
cd /tmp/sshfs
|
||
for i in dev proc sys; do mount --bind /$i $i; done
|
||
chroot /tmp/sshfs
|
||
|
||
Now we can run
|
||
|
||
::
|
||
|
||
borg extract /borgrepo::archive PATH
|
||
|
||
to partially restore whatever we like. Finally, do the clean-up:
|
||
|
||
::
|
||
|
||
exit # exit chroot
|
||
rm /tmp/sshfs/usr/local/bin/borg
|
||
cd /tmp/sshfs
|
||
for i in dev proc sys borgrepo; do umount ./$i; done
|
||
rmdir borgrepo
|
||
cd ~
|
||
umount /tmp/sshfs
|
||
rmdir /tmp/sshfs
|
||
|
||
Full restore
|
||
~~~~~~~~~~~~
|
||
|
||
When doing a full restore, we restore all files (including the ones containing
|
||
the ID-to-name mapping, ``/etc/passwd`` and ``/etc/group``). Everything will be
|
||
consistent automatically if we restore the numeric IDs stored in the archive. So
|
||
there is no need for a chroot environment; we just mount the client file system
|
||
and extract a backup, utilizing the ``--numeric-owner`` option:
|
||
|
||
::
|
||
|
||
sshfs root@host:/ /mnt/sshfs
|
||
cd /mnt/sshfs
|
||
borg extract --numeric-owner /path/to/repo::archive
|
||
cd ~
|
||
umount /mnt/sshfs
|
||
|
||
Simple (lossy) full restore
|
||
~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||
|
||
Using ``borg export-tar`` it is possible to stream a backup to the client and
|
||
directly extract it without the need of mounting with SSHFS:
|
||
|
||
::
|
||
|
||
borg export-tar /path/to/repo::archive - | ssh root@host 'tar -C / -x'
|
||
|
||
Note that in this scenario the tar format is the limiting factor – it cannot
|
||
restore all the advanced features that BorgBackup supports. See
|
||
:ref:`borg_export-tar` for limitations.
|