Add lockfile support

README.md

@@ -64,6 +64,8 @@ Command line options:
 -q    Suppress warnings
 -r    Restic repo name (if using restic)
 -s    Screen name, tmux session name, or hostname:port:password for RCON
+-t    Enable lock file (lock file not used by default)
+-u    Lock file timeout seconds (empty = unlimited)
 -v    Verbose mode
 -w    Window manager: screen (default), tmux, RCON
 ```

backup.sh

@@ -20,6 +20,8 @@ ENABLE_CHAT_MESSAGES=false # Tell players in Minecraft chat about backup status
 PREFIX="Backup" # Shows in the chat message
 DEBUG=false # Enable debug messages
 SUPPRESS_WARNINGS=false # Suppress warnings
+LOCK_FILE="" # Optional lock file to acquire to ensure two backups don't run at once
+LOCK_FILE_TIMEOUT="" # Optional lock file wait timeout (in seconds)
 WINDOW_MANAGER="screen" # Choices: screen, tmux, RCON
 
 # Other Variables (do not modify)
@@ -38,7 +40,7 @@ debug-log () {
   fi
 }
 
-while getopts 'a:cd:e:f:hi:l:m:o:p:qr:s:vw:' FLAG; do
+while getopts 'a:cd:e:f:hi:l:m:o:p:qr:s:t:u:vw:' FLAG; do
   case $FLAG in
     a) COMPRESSION_ALGORITHM=$OPTARG ;;
     c) ENABLE_CHAT_MESSAGES=true ;;
@@ -61,6 +63,8 @@ while getopts 'a:cd:e:f:hi:l:m:o:p:qr:s:vw:' FLAG; do
        echo "-q    Suppress warnings"
        echo "-r    Restic repo name (if using restic)"
        echo "-s    Screen name, tmux session name, or hostname:port:password for RCON"
+       echo "-t    Enable lock file (lock file not used by default)"
+       echo "-u    Lock file timeout seconds (empty = unlimited)"
        echo "-v    Verbose mode"
        echo "-w    Window manager: screen (default), tmux, RCON"
        exit 0
@@ -69,10 +73,12 @@ while getopts 'a:cd:e:f:hi:l:m:o:p:qr:s:vw:' FLAG; do
     l) COMPRESSION_LEVEL=$OPTARG ;;
     m) MAX_BACKUPS=$OPTARG ;;
     o) BACKUP_DIRECTORY=$OPTARG ;;
-    r) RESTIC_REPO=$OPTARG ;;
     p) PREFIX=$OPTARG ;;
     q) SUPPRESS_WARNINGS=true ;;
+    r) RESTIC_REPO=$OPTARG ;;
     s) SCREEN_NAME=$OPTARG ;;
+    t) LOCK_FILE=$OPTARG ;;
+    u) LOCK_FILE_TIMEOUT=$OPTARG ;;
     v) DEBUG=true ;;
     w) WINDOW_MANAGER=$OPTARG ;;
     *) log-fatal "Invalid option -$FLAG"; exit 1 ;;
@@ -467,11 +473,12 @@ clean-up () {
   fi
 }
 
+trap "clean-up" 2
+
+do-backup () {
   # Notify players of start
   message-players "Starting backup..." "$ARCHIVE_FILE_NAME"
 
-trap "clean-up" 2
-
   # Disable world autosaving
   execute-command "save-off"
 
@@ -528,3 +535,18 @@ sync
   END_TIME=$(date +"%s")
 
   clean-up
+}
+
+if [[ "$LOCK_FILE" != "" ]]; then
+  TIMEOUT_OPTION=""
+  if [[ "$LOCK_FILE_TIMEOUT" != "" ]]; then
+    TIMEOUT_OPTION="-w $LOCK_FILE_TIMEOUT"
+  fi
+  (if ! flock $TIMEOUT_OPTION --no-fork 200; then
+      log-fatal "Could not acquire lock on lock file: $LOCK_FILE"
+      exit 1
+    fi
+  do-backup) 200>"$LOCK_FILE"
+else
+  do-backup
+fi

test/test.sh

@@ -80,6 +80,23 @@ check-latest-backup-restic () {
 
 # Tests
 
+test-lock-defaults () {
+  TIMESTAMP="$(date +%F_%H-%M-%S --date="2021-01-01")"
+  ./backup.sh -t "$TEST_TMP/lockfile" -i "$TEST_TMP/server/world" -o "$TEST_TMP/backups" -s "$SCREEN_TMP" -f "$TIMESTAMP"
+  check-backup "$TIMESTAMP.tar.gz"
+  TIMESTAMP="$(date +%F_%H-%M-%S --date="2021-01-01 +1 hour")"
+  ./backup.sh -t "$TEST_TMP/lockfile" -i "$TEST_TMP/server/world" -o "$TEST_TMP/backups" -s "$SCREEN_TMP" -f "$TIMESTAMP"
+  check-backup "$TIMESTAMP.tar.gz"
+}
+
+test-lock-timeout () {
+  TIMESTAMP="$(date +%F_%H-%M-%S --date="2021-01-01")"
+  flock "$TEST_TMP/lockfile" sleep 10 &
+  OUTPUT=$(./backup.sh -t "$TEST_TMP/lockfile" -u 0 -i "$TEST_TMP/server/world" -o "$TEST_TMP/backups" -s "$SCREEN_TMP" -f "$TIMESTAMP")
+  assertNotEquals 0 "$?"
+  assertContains "$OUTPUT" "Could not acquire lock on lock file: $TEST_TMP/lockfile"
+}
+
 test-restic-incomplete-snapshot () {
   chmod 000 "$TEST_TMP/server/world/file1.txt"
   TIMESTAMP="$(date +%F_%H-%M-%S --date="2021-01-01")"