store the list of containers/images kept and removed by docker-gc

copy all files in one command

Update README

README.md

@@ -83,11 +83,11 @@ redis:[^ ]\+
 
 ### Excluding Containers From Garbage Collection
 
-There can also be containers (for example data only containers) which 
-you would like to exclude from garbage collection. To do so, create 
-`/etc/docker-gc-exclude-containers`, or if you want the file to be 
-read from elsewhere, set the `EXCLUDE_CONTAINERS_FROM_GC` environment 
-variable to its location. This file should container name patterns (in 
+There can also be containers (for example data only containers) which
+you would like to exclude from garbage collection. To do so, create
+`/etc/docker-gc-exclude-containers`, or if you want the file to be
+read from elsewhere, set the `EXCLUDE_CONTAINERS_FROM_GC` environment
+variable to its location. This file should container name patterns (in
 the `grep` sense), one per line, such as `mariadb-data`.
 
 An example container excludes file might contain:
@@ -136,6 +136,13 @@ By default, docker-gc will proceed with deletion of containers and images. To te
 DRY_RUN=1 docker-gc
 ```
 
+### Keeping History
+You can configure docker-gc to store a history of images and containers that were removed
+by setting the `LOG_HISTORY` variable to 1.
+
+```
+LOG_HISTORY=1 docker-gc
+```
 
 ## Running as a Docker Image
 

docker-gc

@@ -37,13 +37,14 @@
 # containers were removed. To enable logging to syslog, set LOG_TO_SYSLOG=1.
 # When disabled, this script will instead log to standard out. When syslog is
 # enabled, the syslog facility and logger can be configured with
-# $SYSLOG_FACILITY and $SYSLOG_LEVEL respectively. 
+# $SYSLOG_FACILITY and $SYSLOG_LEVEL respectively.
 
 set -o nounset
 set -o errexit
 
 GRACE_PERIOD_SECONDS=${GRACE_PERIOD_SECONDS:=3600}
 STATE_DIR=${STATE_DIR:=/var/lib/docker-gc}
+LOG_HISTORY=${LOG_HISTORY:=0}
 FORCE_CONTAINER_REMOVAL=${FORCE_CONTAINER_REMOVAL:=0}
 FORCE_IMAGE_REMOVAL=${FORCE_IMAGE_REMOVAL:=0}
 DOCKER=${DOCKER:=docker}
@@ -75,7 +76,7 @@ fi
 EXCLUDE_CONTAINERS_FROM_GC=${EXCLUDE_CONTAINERS_FROM_GC:=/etc/docker-gc-exclude-containers}
 if [ ! -f "$EXCLUDE_CONTAINERS_FROM_GC" ]
 then
-  EXCLUDE_CONTAINERS_FROM_GC=/dev/null  
+  EXCLUDE_CONTAINERS_FROM_GC=/dev/null
 fi
 
 EXCLUDE_IDS_FILE="exclude_ids"
@@ -143,7 +144,7 @@ function compute_exclude_container_ids() {
         return
     fi
     # Find all docker images
-    # Filter out with matching names 
+    # Filter out with matching names
     # and put them to $EXCLUDE_CONTAINER_IDS_FILE
     $DOCKER ps -a \
         | grep -E "$PROCESSED_EXCLUDES" \
@@ -272,3 +273,10 @@ else
     image_log "Removing image" images.reap
     xargs -n 1 $DOCKER rmi $FORCE_IMAGE_FLAG < images.reap &>/dev/null || true
 fi
+
+if [[ $LOG_HISTORY -gt 0 ]]; then
+  timestamp=$(date +"%H-%M-%S-%Y-%m-%d")
+  log "Saving docker gc history under $STATE_DIR/history/$timestamp"
+  mkdir -p $STATE_DIR/history/$timestamp
+  cp $STATE_DIR/{images.reap,images.used,container.reap,container.keep} $STATE_DIR/history/$timestamp
+fi