# Avrdude: ser\_open(): can't open device "\\\\.\\COM5": etc **URL:** \ **Category:** Uploading\ **Created:** [August 11, 2025, 7:51am UTC](https://forum.arduino.cc/t/avrdude-ser-open-cant-open-device-com5-etc/1401605 "2025-08-11T07:51:46Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![Nick\_Pyner](https://avatars.discourse-cdn.com/v4/letter/n/e8c25b/32.png) [@Nick\_Pyner](https://forum.arduino.cc/u/Nick_Pyner)\ **Post date:** [August 11, 2025, 7:51am UTC](https://forum.arduino.cc/t/avrdude-ser-open-cant-open-device-com5-etc/1401605/1 "2025-08-11T07:51:46Z")
It’s a while since I have uploaded anything, but I’m sure I have never seen this before. The IDE and W10’s DeviceManager both declare my Mega is on COM4. The above is at the start of my upload but there is a swag of other stuff following. It’s all about comms too. I have seen some post about uploading with Arduino disconnected. Needless to say, I can’t do that… ---
**Author:** ![Nick\_Pyner](https://avatars.discourse-cdn.com/v4/letter/n/e8c25b/32.png) [@Nick\_Pyner](https://forum.arduino.cc/u/Nick_Pyner)\ **Post date:** [August 11, 2025, 8:03am UTC](https://forum.arduino.cc/t/avrdude-ser-open-cant-open-device-com5-etc/1401605/2 "2025-08-11T08:03:32Z")
It’s OK and the panic is over… I fixed it by plugging the cable into a different USB port. I really don’t know where the problem lies, I have had no reason to suspect the port. I would suggest to anybody who has this problem that they just try another port before getting into anything more complicated ---
**Author:** ![sterretje](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/sterretje/32/391294_2.png) [@sterretje](https://forum.arduino.cc/u/sterretje)\ **Post date:** [August 11, 2025, 8:05am UTC](https://forum.arduino.cc/t/avrdude-ser-open-cant-open-device-com5-etc/1401605/3 "2025-08-11T08:05:48Z")
Sometimes it's advisable to clean out the drivers in device manager. ---
**Author:** ![Dozie](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/dozie/32/239024_2.png) [@Dozie](https://forum.arduino.cc/u/Dozie)\ **Post date:** [August 11, 2025, 8:29am UTC](https://forum.arduino.cc/t/avrdude-ser-open-cant-open-device-com5-etc/1401605/4 "2025-08-11T08:29:19Z")
Take a look at ['Error: avrdude' when uploading](https://support.arduino.cc/hc/en-us/search/click?data=BAh7DjoHaWRsKwgS5yfkAAQ6D2FjY291bnRfaWRpA07KIDoJdHlwZUkiDGFydGljbGUGOgZFVDoIdXJsSSJdaHR0cHM6Ly9zdXBwb3J0LmFyZHVpbm8uY2MvaGMvZW4tdXMvYXJ0aWNsZXMvNDQwMTg3NDMzMTQxMC0tRXJyb3ItYXZyZHVkZS13aGVuLXVwbG9hZGluZwY7CFQ6DnNlYXJjaF9pZEkiKTI0MDYwMmI3LTgzOWYtNGMzMy1iNWRkLTRkNDA2ZDhlZWM5MgY7CEY6CXJhbmtpBjoLbG9jYWxlSSIKZW4tdXMGOwhUOgpxdWVyeUkiNkF2cmR1ZGU6IHNlcl9vcGVuKCk6IGNhbid0IG9wZW4gZGV2aWNlICJcXC5cQ09NNSIGOwhUOhJyZXN1bHRzX2NvdW50aQY%3D--8df24d1149531c5e3948f525ccae441a04a44d23) ---
**Author:** ![worldleader](https://avatars.discourse-cdn.com/v4/letter/w/a87d85/32.png) [@worldleader](https://forum.arduino.cc/u/worldleader)\ **Post date:** [August 15, 2025, 7:36pm UTC](https://forum.arduino.cc/t/avrdude-ser-open-cant-open-device-com5-etc/1401605/5 "2025-08-15T19:36:42Z")
it happens to me as well ---
**Author:** ![worldleader](https://avatars.discourse-cdn.com/v4/letter/w/a87d85/32.png) [@worldleader](https://forum.arduino.cc/u/worldleader)\ **Post date:** [August 15, 2025, 7:38pm UTC](https://forum.arduino.cc/t/avrdude-ser-open-cant-open-device-com5-etc/1401605/6 "2025-08-15T19:38:23Z")
when i have not defined the port/com ---
**Author:** ![worldleader](https://avatars.discourse-cdn.com/v4/letter/w/a87d85/32.png) [@worldleader](https://forum.arduino.cc/u/worldleader)\ **Post date:** [August 15, 2025, 7:43pm UTC](https://forum.arduino.cc/t/avrdude-ser-open-cant-open-device-com5-etc/1401605/7 "2025-08-15T19:43:08Z")
to connect click where the arow is pointing ![image](https://europe1.discourse-cdn.com/arduino/original/4X/e/e/7/ee7892dbfb25d5c0bf59b49547d38990b03e5b2a.png) ---
**Author:** ![worldleader](https://avatars.discourse-cdn.com/v4/letter/w/a87d85/32.png) [@worldleader](https://forum.arduino.cc/u/worldleader)\ **Post date:** [August 15, 2025, 7:50pm UTC](https://forum.arduino.cc/t/avrdude-ser-open-cant-open-device-com5-etc/1401605/8 "2025-08-15T19:50:25Z")
once you have clicked there it should look like this: ![image](https://europe1.discourse-cdn.com/arduino/original/4X/3/f/5/3f530dbfca3d5046f2896332c823d277e86a58ef.png) once your board is plugged in, and no other devises are plugged in, click on any port/com that appears. define the board. and upload your code! ---
**Author:** ![worldleader](https://avatars.discourse-cdn.com/v4/letter/w/a87d85/32.png) [@worldleader](https://forum.arduino.cc/u/worldleader)\ **Post date:** [August 15, 2025, 7:50pm UTC](https://forum.arduino.cc/t/avrdude-ser-open-cant-open-device-com5-etc/1401605/9 "2025-08-15T19:50:57Z")
hope that fixes your problem ---
**Author:** ![Nick\_Pyner](https://avatars.discourse-cdn.com/v4/letter/n/e8c25b/32.png) [@Nick\_Pyner](https://forum.arduino.cc/u/Nick_Pyner)\ **Post date:** [August 16, 2025, 12:21am UTC](https://forum.arduino.cc/t/avrdude-ser-open-cant-open-device-com5-etc/1401605/10 "2025-08-16T00:21:40Z")
My IDE said Mega was on COM4 and Windows agreed. Windows also said everything is fine. This is not as simple as you seem to think no it is, and what I did to fix it is not necessarily the solution for everybody. ---
**Author:** ![system](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/system/32/1140315_2.png) [@system](https://forum.arduino.cc/u/system)\ **Post date:** [February 12, 2026, 12:22am UTC](https://forum.arduino.cc/t/avrdude-ser-open-cant-open-device-com5-etc/1401605/11 "2026-02-12T00:22:30Z")
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