Btrfs snapshots make for easy backups. 
Possibly – and, only with the caveat of the current list of “btrfs-receive” bugs –
BUGS
btrfs receive sets the subvolume read-only after it completes successfully. However, while the receive is in
progress, users who have write access to files or directories in the receiving path can add, remove, or modify
files, in which case the resulting read-only subvolume will not be an exact copy of the sent subvolume.
If the intention is to create an exact copy, the receiving path should be protected from access by users until
the receive operation has completed and the subvolume is set to read-only.
Additionally, receive does not currently do a very good job of validating that an incremental send stream
actually makes sense, and it is thus possible for a specially crafted send stream to create a subvolume with
reflinks to arbitrary files in the same filesystem. Because of this, users are advised to not use btrfs
receive on send streams from untrusted sources, and to protect trusted streams when sending them across
untrusted networks.
Continuing the discussion from Backup/Restore btrfs. Howto restore snapper snapshots after disaster recovery (btrfs send/receive)?:
Backups are easy, efficient and secure
Source partition
6700k:~ # findmnt /
TARGET SOURCE FSTYPE OPTIONS
/ /dev/sda8[/@/.snapshots/236/snapshot] btrfs rw,relatime,ssd,space_cache,subvolid=700,subvol=/@/.snapshots/236/snapshot
6700k:~ #
Target partition
6700k:~ # findmnt /mnt
TARGET SOURCE FSTYPE OPTIONS
/mnt /dev/sdc5[/@/.snapshots/1/snapshot] btrfs rw,relatime,ssd,space_cache=v2,subvolid=266,subvol=/@/.snapshots/1/snapshot
6700k:~ #
Backup commands
Full backup
mkdir -p /mnt/backup/245
btrfs send /.snapshots/245/snapshot/ | btrfs receive /mnt/backup/245
Incremental backup
mkdir /mnt/backup/266
btrfs send -p /.snapshots/245/snapshot/ /.snapshots/266/snapshot/ | btrfs receive /mnt/backup/266
Restore
Each of the following subvolumes is a full backup and may be restored by a single command:
6700k:~ # btrfs subvolume list -t /mnt
ID gen top level path
-- --- --------- ----
256 31 5 @
....
282 951 266 backup/245/snapshot
283 958 266 backup/266/snapshot
284 961 266 backup/273/snapshot
6700k:~ #
btrfs send /mnt/backup/267/snapshot | btrfs receive /.snapshots/267/
I want to do a backup daily at login of the last valid snapshot.
How can I find out, eg at login which is the last valid snapshot
Evaluating btrbk backup on infamous host erlangen
Terse configuration of btrbk:
thinkbook:~ # cat /etc/btrbk/btrbk.conf
transaction_log /var/log/btrbk.log
snapshot_dir /BTRBK/btrbk_snapshots
target ssh://erlangen.fritz.box/Backup/btrbk_snapshots/thinkbook
subvolume /home
thinkbook:~ #
btrbk list
thinkbook:~ # btrbk list
SOURCE_SUBVOLUME SNAPSHOT_SUBVOLUME STATUS TARGET_HOST TARGET_SUBVOLUME
/home /BTRBK/btrbk_snapshots/home.20230712T0906 - erlangen.fritz.box /Backup/btrbk_snapshots/thinkbook/home.20230712T0906
/home /BTRBK/btrbk_snapshots/home.20230712T1341 - erlangen.fritz.box /Backup/btrbk_snapshots/thinkbook/home.20230712T1341
thinkbook:~ #
Test run
thinkbook:~ # time btrbk run
--------------------------------------------------------------------------------
Backup Summary (btrbk command line client, version 0.32.6)
Date: Wed Jul 12 14:28:05 2023
Config: /etc/btrbk/btrbk.conf
Legend:
=== up-to-date subvolume (source snapshot)
+++ created subvolume (source snapshot)
--- deleted subvolume
*** received subvolume (non-incremental)
>>> received subvolume (incremental)
--------------------------------------------------------------------------------
/home
+++ /BTRBK/btrbk_snapshots/home.20230712T1428
>>> erlangen.fritz.box:/Backup/btrbk_snapshots/thinkbook/home.20230712T1428
real 0m3.701s
user 0m0.729s
sys 0m0.139s
thinkbook:~ #