diff --git a/copyparty/__main__.py b/copyparty/__main__.py
index 04c63b48..d4f8e2fd 100755
--- a/copyparty/__main__.py
+++ b/copyparty/__main__.py
@@ -749,7 +749,7 @@ def run_argparse(argv: list[str], formatter: Any, retry: bool) -> argparse.Names
     ap2.add_argument("--no-scandir", action="store_true", help="disable scandir; instead using listdir + stat on each file")
     ap2.add_argument("--no-fastboot", action="store_true", help="wait for up2k indexing before starting the httpd")
     ap2.add_argument("--no-htp", action="store_true", help="disable httpserver threadpool, create threads as-needed instead")
-    ap2.add_argument("--stackmon", metavar="P,S", type=u, help="write stacktrace to Path every S second")
+    ap2.add_argument("--stackmon", metavar="P,S", type=u, help="write stacktrace to Path every S second, for example --stackmon=./st/%Y-%m/%d/%H%M.xz,60")
     ap2.add_argument("--log-thrs", metavar="SEC", type=float, help="list active threads every SEC")
     ap2.add_argument("--log-fk", metavar="REGEX", type=u, default="", help="log filekey params for files where path matches REGEX; '.' (a single dot) = all files")
     # fmt: on
diff --git a/copyparty/util.py b/copyparty/util.py
index 3368305b..02c5b4ae 100644
--- a/copyparty/util.py
+++ b/copyparty/util.py
@@ -707,12 +707,43 @@ def start_stackmon(arg_str: str, nid: int) -> None:
 
 def stackmon(fp: str, ival: float, suffix: str) -> None:
     ctr = 0
+    fp0 = fp
     while True:
         ctr += 1
+        fp = fp0
         time.sleep(ival)
         st = "{}, {}\n{}".format(ctr, time.time(), alltrace())
+        buf = st.encode("utf-8", "replace")
+
+        if fp.endswith(".gz"):
+            import gzip
+
+            # 2459b 2304b 2241b 2202b 2194b 2191b lv3..8
+            # 0.06s 0.08s 0.11s 0.13s 0.16s 0.19s
+            buf = gzip.compress(buf, compresslevel=6)
+
+        elif fp.endswith(".xz"):
+            import lzma
+
+            # 2276b 2216b 2200b 2192b 2168b lv0..4
+            # 0.04s 0.10s 0.22s 0.41s 0.70s
+            buf = lzma.compress(buf, preset=0)
+
+        if "%" in fp:
+            dt = datetime.utcnow()
+            for fs in "YmdHMS":
+                fs = "%" + fs
+                if fs in fp:
+                    fp = fp.replace(fs, dt.strftime(fs))
+
+        if "/" in fp:
+            try:
+                os.makedirs(fp.rsplit("/", 1)[0])
+            except:
+                pass
+
         with open(fp + suffix, "wb") as f:
-            f.write(st.encode("utf-8", "replace"))
+            f.write(buf)
 
 
 def start_log_thrs(