documentation: added documentation of "resume_missing" option

ChangeLog

@@ -24,5 +24,9 @@
 * btrbk-current
   - added configuration option "btrfs_progs_compat", to be enabled if
     using btrfs-progs < 3.17. Fixes issue #6
+  - added configuration option "resume_missing", for automatic resume
+    of missing backups
   - removed configuration option "receive_log" in favor of printing
     errors from "btrfs receive"
+  - bugfix: show correct exit code on external command failure
+  - bugfix: no crash if "commit_delete" option is set to "no"

README.md

@@ -14,9 +14,10 @@ Key Features:
 
 - Atomic snapshots
 - Incremental backups
+- Configurable retention policy
 - Backups to multiple destinations
 - Transfer via ssh
-- Configurable retention policy
+- Resume of backups (if backup disk was not attached for a while)
 - Display file changes between two backups
 
 btrbk is intended to be run as a cron job.

btrbk.conf.example

@@ -23,7 +23,8 @@ incremental                yes
 # Always create snapshots, even if the target volume is unreachable
 snapshot_create_always     yes
 
-# Resume missing backups of snapshots
+# Resume missing backups if the target volume is reachable again.
+# Useful in conjunction with "snapshot_create_always".
 resume_missing             yes
 
 # ssh key for ssh volumes/targets

doc/btrbk.1

@@ -62,7 +62,8 @@ subvolumes specified in the configuration file.
 Then, for each specified target, btrbk creates a new backup subvolume,
 incremental from the latest common snapshot / backup subvolume
 found. If no common parent subvolume is found, a full backup is
-created.
+created. This is also done for all missing backups if the
+\fIresume_missing\fR option is set.
 .PP
 In a last step, previous snapshots and backup subvolumes that are not
 preserved by their configured retention policy will be deleted. This

doc/btrbk.conf.5

@@ -45,16 +45,24 @@ Directory in which the btrfs snapshots are created. Relative to
 does not autmatically create this directory, and the snapshot creation
 will fail if it is not present.
 .TP
-\fBsnapshot_create_always\fR  yes|no
-If set, the snapshots are always created, even if the backup subvolume
-cannot be created (e.g. if the target subvolume cannot be
-reached). Defaults to \(lqno\(rq. Useful for subvolumes on laptops to
-make sure the snapshots are created even if you are on the road.
-.TP
 \fBincremental\fR  yes|no|strict
 Perform incremental backups. Defaults to \(lqyes\(rq. If set to
 \(lqstrict\(rq, non-incremental (initial) backups are never created.
 .TP
+\fBsnapshot_create_always\fR  yes|no
+If set, the snapshots are always created, even if the backup subvolume
+cannot be created (e.g. if the target subvolume cannot be
+reached). Use in conjunction with the \fIresume_missing\fR option to
+make sure that the backups are created as soon as the target subvolume
+is reachable again. Useful for laptop filesystems in order to make
+sure the snapshots are created even if you are on the road. Defaults
+to \(lqno\(rq.
+.TP
+\fBresume_missing\fR  yes|no
+If set, the backups in the target directory are compared to the source
+snapshots, and missing backups are created if needed (complying to the
+target preserve matrix). Defaults to \(lqyes\(rq.
+.TP
 \fBtarget_preserve_daily\fR  all|<number>
 How many days of backups should be preserved. Defaults to \(lqall\(rq.
 .TP