diff --git a/.gitignore b/.gitignore
index 6de205ad..f06fcdef 100644
--- a/.gitignore
+++ b/.gitignore
@@ -68,6 +68,9 @@ tests/*.log
 tests/*.trs
 tests/logs/
 
+# Mass update logs
+logs/
+
 # Test binaries (files without extension in tests/)
 tests/test_*
 tests/bench_*
diff --git a/tools/mass_update.py b/tools/mass_update.py
index d7e29f0f..6970455c 100755
--- a/tools/mass_update.py
+++ b/tools/mass_update.py
@@ -19,7 +19,6 @@ SSH keys: tools/keys/ (in script directory)
 
 import argparse
 import json
-import os
 import subprocess
 import sys
 from concurrent.futures import ThreadPoolExecutor, as_completed
@@ -67,8 +66,8 @@ def load_servers(config_path, script_dir):
     return servers
 
 
-def update_server(server, command):
-    """Run update on a single server via SSH."""
+def update_server(server, command, logs_dir):
+    """Run update on a single server via SSH. Returns result dict with logs_dir for log writing."""
     host = server["host"]
     port = server.get("port", 22)
     workdir = server.get("workdir", "~/utun")
@@ -94,26 +93,50 @@ def update_server(server, command):
             text=True,
             timeout=SSH_TIMEOUT
         )
-        return {
+        return write_log({
             "host": host,
             "returncode": result.returncode,
             "stdout": result.stdout,
             "stderr": result.stderr
-        }
+        }, logs_dir)
     except subprocess.TimeoutExpired:
-        return {
+        return write_log({
             "host": host,
             "returncode": -1,
             "stdout": "",
             "stderr": f"Timeout after {SSH_TIMEOUT}s"
-        }
+        }, logs_dir)
     except Exception as e:
-        return {
+        return write_log({
             "host": host,
             "returncode": -1,
             "stdout": "",
             "stderr": str(e)
-        }
+        }, logs_dir)
+
+
+def write_log(result, logs_dir):
+    """Write session log to file. Returns result dict."""
+    host = result["host"]
+    rc = result["returncode"]
+    log_path = logs_dir / f"{host}.log"
+    try:
+        with open(log_path, 'w') as f:
+            f.write(f"Host: {host}  |  Exit code: {rc}\n")
+            f.write("=" * 60 + "\n")
+            if result["stdout"]:
+                f.write(result["stdout"])
+                if not result["stdout"].endswith("\n"):
+                    f.write("\n")
+            if result["stderr"]:
+                f.write("STDERR:\n")
+                f.write(result["stderr"])
+                if not result["stderr"].endswith("\n"):
+                    f.write("\n")
+        result["_log_file"] = str(log_path)
+    except Exception as e:
+        result["_log_file"] = f"ERROR writing log: {e}"
+    return result
 
 
 def main():
@@ -167,9 +190,13 @@ def main():
         print("ERROR: No servers found in config", file=sys.stderr)
         sys.exit(1)
 
+    logs_dir = Path("logs")
+    logs_dir.mkdir(parents=True, exist_ok=True)
+
     print(f"Updating {len(servers)} servers in '{args.command}' mode...")
     print(f"Parallel jobs: {args.jobs}")
     print(f"Config: {config_path}")
+    print(f"Logs: {logs_dir.resolve()}")
     print()
 
     success = 0
@@ -177,7 +204,7 @@ def main():
 
     with ThreadPoolExecutor(max_workers=args.jobs) as executor:
         futures = {
-            executor.submit(update_server, s, args.command): s
+            executor.submit(update_server, s, args.command, logs_dir): s
             for s in servers
         }
 
@@ -186,19 +213,17 @@ def main():
             host = result["host"]
             rc = result["returncode"]
 
-            print(f"{'='*60}")
-            print(f"Host: {host}  |  Exit code: {rc}")
-            print(f"{'='*60}")
-
-            if result["stdout"]:
-                print(result["stdout"])
-            if result["stderr"]:
-                print(result["stderr"], file=sys.stderr, end="")
-
             if rc == 0:
                 success += 1
             else:
                 failed += 1
+                print(f"{'='*60}")
+                print(f"Host: {host}  |  Exit code: {rc}  |  Log: {result.get('_log_file', 'N/A')}")
+                print(f"{'='*60}")
+                if result["stdout"]:
+                    print(result["stdout"])
+                if result["stderr"]:
+                    print(result["stderr"], file=sys.stderr, end="")
 
     print(f"{'='*60}")
     print(f"Done: {success} succeeded, {failed} failed")