Allow for existing user or group

Fix chown syntax

scripts/postinst.sh

@@ -7,8 +7,9 @@ set -e
 if [ "$1" = "configure" ] || [ "$1" -ge 1 ]; then
   if [ -d /run/systemd/system ]; then
     # Create ntfy user/group
-    id ntfy >/dev/null 2>&1 || useradd --system --no-create-home ntfy
-    chown ntfy.ntfy /var/cache/ntfy /var/cache/ntfy/attachments /var/lib/ntfy
+    groupadd -f ntfy
+    id ntfy >/dev/null 2>&1 || useradd --system --no-create-home -g ntfy ntfy
+    chown ntfy:ntfy /var/cache/ntfy /var/cache/ntfy/attachments /var/lib/ntfy
     chmod 700 /var/cache/ntfy /var/cache/ntfy/attachments /var/lib/ntfy
 
     # Hack to change permissions on cache file
@@ -16,7 +17,7 @@ if [ "$1" = "configure" ] || [ "$1" -ge 1 ]; then
     if [ -f "$configfile" ]; then
       cachefile="$(cat "$configfile" | perl -n -e'/^\s*cache-file: ["'"'"']?([^"'"'"']+)["'"'"']?/ && print $1')" # Oh my, see #47
       if [ -n "$cachefile" ]; then
-        chown ntfy.ntfy "$cachefile" || true
+        chown ntfy:ntfy "$cachefile" || true
         chmod 600 "$cachefile" || true
       fi
     fi