Linux dev ttyusb0 permissions

Fix serial port permission denied errors on Linux

The ancient serial port which is no longer found on the latest motherboards and even the not so latest laptops is still used for connecting to the console of networking devices, headless computers and a lot other applications. On computers which do not have built-in serial ports USB-to-Serial adapters can be used. Linux identifies inbuilt serial ports as /dev/ttyS0, /dev/ttyS1,….. /dev/ttySn and USB-to-Serial adapters as /dev/ttyUSB0, …. /dev/ttyUSBn and they can be accessed using terminal emulator applications like PuTTY, minicom and screen.

Normally when the serial console is accessed using the terminal emulator of your choice as a non-root user you’ll get a “permission denied” error. Using PuTTY on Ubuntu I got the following error – “Unable to open connection to: Unable to open serial port“.

PuTTY on Linux throws this error if the user running it does not have permissions to access the serial port device file

This is because the device file of the serial port does not have permissions to allow to currently logged in user to “read” or “write” to the serial device. The following command will confirm that.

So we can see that only the “root” user and the “dialout” group have proper permissions, while chmod can be used to grant access to the required user or everyone it is messy and not a secure way. The easier way is the add the user to the dialout group.

First verify if the user does belong to the dialout group using the “id” command.

Next add the user to the “dialout” supplementary group.

You have to logout and login before changes take effect. After logging back in try the “id” command again.

Now all your terminal emulator applications will work with the serial port without any issues.

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Configure permissions for /dev/ttyUSB0

I’m trying to communicate with an Arduino from Ubuntu 12.04. When plugging in the USB cable, the arduino’s serial port occurs as /dev/ttyUSB0. When I try to connect to it using moserial, I’m getting an «Could not open device /dev/ttyUSB0» error, but not when I launch moserial using sudo. What I have to configure to make the serial device accessible as normal non-root user?

1 Answer 1

You have several options:

Automatic ACL assignment

You most likely have systemd-logind or ConsoleKit running in Ubuntu, which can automatically configure ACLs on device nodes based on which user account is currenty logged in at the console. These ACLs grant access additionally to the usual permissions and can be seen using getfacl .

To use this, add the following to /etc/udev/rules.d/60-extra-acl.rules 1 :

( 1 Yes, create the file. It doesn’t exist by default; the whole directory is for admin customizations.)

Group-based access

The tty devices are usually readable/writable by a specific group such as «dialout» or «uucp». Add yourself to that group to gain access to all serial ports:

Don’t forget to log out & log in again so that group changes get applied.

Permission or ownership changes

udev rules similar to above can also be used to set the «main» owner & group as well as the permissions (which is how the default group got set in the first place). For example:

You can assign to OWNER, GROUP, and MODE parameters.

Temporary manual change

To do a one-time change, just use chmod and/or chown as you normally would.

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Как мне разрешить не-root доступ к / ttyUSB0?

Поскольку я обновил с 10.04 до 12.04, я не могу получить доступ к устройству, подключенному в / ttyUSB0, если у меня нет root-доступа. Чтобы быть более точным, я использую преобразователь последовательного порта USB в последовательный порт для доступа и настройки оборудования Cisco с помощью программного обеспечения Putty . Случается, что, так как я обновил до 12.04, Putty видит подключенное устройство, только когда я запускаю его как gksudo putty . Если нет, он говорит «невозможно подключиться к порту / ttyUSB0». Мне удалось изменить разрешения через CHMOD 666, и это работает, но если я отключаю USB и снова подключаюсь, он возвращается только к root. Как мне разрешить постоянный доступ без полномочий root? У меня есть подсказка, что это может быть с помощью правил udev, но я не знаю, как это сделать.

обсервованный Производитель и драйверы «ПРОЛИФИК»

Возможно, это связано с modemmanager , как подробно описано здесь .

Я удалил это ( sudo apt-get remove modemmanager ), и это решило мою проблему.

Вы все еще должны быть в dialout группе, хотя.

Устройство, скорее всего, подключено к группе пользователей dialout . Просто добавьте своего пользователя в группу дозвона, чтобы иметь соответствующие разрешения на устройстве.

(Вам может потребоваться выйти из системы и снова войти в нее, чтобы новая группа вступила в силу.)

Не нужно возиться с разрешениями или правилами udev.

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Cannot open /dev/ttyUSB0: Permission denied #26

Comments

Navis-Raven commented Jul 18, 2017

I had an issue , while trying to do flash
Cannot open /dev/ttyUSB0: Permission denied

I palliated to this problem with the command » sudo chmod -R 777 /dev/ttyUSB0 » each time I wanted to flash.

Do you know more about these bugs ? This maybe due to an ubuntu bug (Ubuntu 16 LTS) but I don’t know

The text was updated successfully, but these errors were encountered:

ConstantJoe commented Aug 8, 2017

I’m not a dev on this project, just a user so if anyone else wants to jump in please do:

This is not an issue with the esp8266, and its not actually a bug at all, its just part of Linux. Its best practice to not change permissions in /dev unless as a last resort. What you want to do instead is to add yourself to the group which would give you permission to access the tty ports.

To see the groups you are in simply type:

To see all available groups type:

Most of them are self-explanatory, in this case you want to add yourself to either the tty group, or dialout, which you would do by:

sudo usermod -a -G tty yourname

Then your user should have access to tty without use of sudo.

stefanofiorentino commented Mar 28, 2018

After the sudo usermod -a -G tty yourname you have to logout/login to get group addition happens.

kbhuinfo commented Jan 22, 2019

I had to add my user to group «dialout» too (ubuntu). Logout/login required.

bumbalu commented Feb 13, 2019

Thank you people, it helped me to get access to my 3d printer from Klipper on Raspberry Pi!

abstract17 commented Mar 29, 2019

PROPER LOGOUT IS REQUIRED

Taudris commented Apr 21, 2019

Can this issue be added to the install documentation? Or even better, is there a way to automate handling it?

shamo1 commented Nov 11, 2019

this is actually a permission problem u have to allow your Arduino IDE to access the specified port just simply type following commands in your terminal

sudo su
//type your password
cd /
cd dev
chown username ttyUSB0

fr3kz commented Nov 11, 2019

thank you shamo1, it helped me

Vince55 commented Jan 20, 2020

thanks shamo1, that worked for me too!

tdgi commented Jan 24, 2020

I add myself to dialout group and it works:
sudo usermod -a -G dialout your_user_name

BlagoD commented Feb 10, 2020

I had to add my user to group «dialout» too (ubuntu). Logout/login required.

Indeed, without being member of the «dialout» group, the access to the ttyUSB is not granted.
Thanks for pointing it out!

m-atoms commented May 19, 2020

note for future users who are curious about this

Problem
Cannot open /dev/ttyUSB0: Permission denied error is caused by the user not having access to the serial ports as other commenters have mentioned. More specifically, the user is not in the dialout group.

Solution
sudo usermod -a -G dialout $USER

For anyone who likes knowing what they’re running before they run it:
usermod — modify a user account
-a — add the user to supplementary groups
-G — a list of supplementary groups (man page says to use -a only with -G )
dialout — group that controls access to serial ports (and other hardware too)
$USER — Bash variable containing current username (not a builtin, usually automatically set env variable)

bonus notes: This is the ‘linux way’ to solve the problem. Adding the user to the group with permission to use the device is much safer than changing the permissions of the device itself. And as others have mentioned, make sure you log out for the changes to take effect.

thecompoundingdev commented Jun 9, 2020 •

thanks @shamo1 ! I tried adding myself to tty and dialout group and it worked after logging back in. but the next day it gave same error but I was still a member of those groups. Had to add chown ttyUSB0 through root and it worked!

hashc4t commented Jun 25, 2020

For anyone using Arch Linux, Arch has a separate user group for serial ports called uucp.
To add your current user:
sudo usermod -a -G uucp $USER
then logout/login.

duncanhames commented Jul 6, 2020

For anyone using Arch Linux, Arch has a separate user group for serial ports called uucp.
To add your current user:
sudo usermod -a -G uucp $USER
then logout/login.

Thanks for that!

kaustubhKVS commented Jul 13, 2020

this is actually a permission problem u have to allow your Arduino IDE to access the specified port just simply type following commands in your terminal

sudo su
//type your password
cd /
cd dev
chown username ttyUSB0

This worked better for me !! They should include this on documentation !! Thankyou @shamo1 .

ThomasGeor commented Oct 9, 2020

this is actually a permission problem u have to allow your Arduino IDE to access the specified port just simply type following commands in your terminal

sudo su
//type your password
cd /
cd dev
chown username ttyUSB0

This one worked for me with ESP32

loleg commented Oct 30, 2020

In addition to adding my user to the tty and dialout groups on Fedora Linux 32, I also had to follow the instructions here:

On modern distros that use ConsoleKit create the file /etc/udev/rules.d/01-ttyusb.rules containing the following and then reload the udev rules and replug the Arduino device:

kelvin-JR commented Nov 3, 2020

this is actually a permission problem u have to allow your Arduino IDE to access the specified port just simply type following commands in your terminal

sudo su
//type your password
cd /
cd dev
chown username ttyUSB0

it’s helpful ,thank you

diesilveira commented Nov 12, 2020

RicBar10 commented Nov 18, 2020

this is actually a permission problem u have to allow your Arduino IDE to access the specified port just simply type following commands in your terminal

sudo su
//type your password
cd /
cd dev
chown username ttyUSB0

thanks you, it solve the problem, you’re a genius

Bill0412 commented Nov 21, 2020

this is actually a permission problem u have to allow your Arduino IDE to access the specified port just simply type following commands in your terminal

sudo su
//type your password
cd /
cd dev
chown username ttyUSB0

This solves my problem, thanks!

cheng3100 commented Jan 27, 2021

Hi ,just look at this issue and I found a better solution .
Just type this commad to install a udev ruler file:

This ruler file is from platformio.

And you also need to join group dialout and plugdev :

stefanofiorentino commented Jan 27, 2021

And you also need to join group dialout and plugdev:

and remember to logout/login..

MohamedYousof commented Feb 4, 2021

this is actually a permission problem u have to allow your Arduino IDE to access the specified port just simply type following commands in your terminal

sudo su
//type your password
cd /
cd dev
chown username ttyUSB0

This worked for me Ubuntu 20.04

peely commented Feb 10, 2021 •

note for future users who are curious about this

Problem
Cannot open /dev/ttyUSB0: Permission denied error is caused by the user not having access to the serial ports as other commenters have mentioned. More specifically, the user is not in the dialout group.

Solution
sudo usermod -a -G dialout $USER

For anyone who likes knowing what they’re running before they run it:
usermod — modify a user account
-a — add the user to supplementary groups
-G — a list of supplementary groups (man page says to use -a only with -G )
dialout — group that controls access to serial ports (and other hardware too)
$USER — Bash variable containing current username (not a builtin, usually automatically set env variable)

bonus notes: This is the ‘linux way’ to solve the problem. Adding the user to the group with permission to use the device is much safer than changing the permissions of the device itself. And as others have mentioned, make sure you log out for the changes to take effect.

This is the safest, cleanest and most reliable answer. Don’t just go round changing ownership, make yourself a member of that devices ownership group. Thank you @m-atoms for the clear explanation.

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Serial port terminal > Cannot open /dev/ttyS0: Permission denied

I had Windows XP on this box and it failed. Thinking it was corrupted OS I tried to reinstall, and it failed. But then I tried to install Ubuntu, and I could not run it from the USB or from the HD.

Did the mem test and found out one of my 512MB sticks (had 2) failed. I removed the bad one and was able to install Ubuntu but it was sluggish.

I was trying to quickly setup my packet radio for Hurricane Sandy. Downloaded the Serial Port Terminal and was able to get some use but the system kept locking up. So Installed Xubuntu next to it, planning on running out the next day to get RAM for the box. Put Xubuntu on and now I am getting the following error with serial port terminal.:

I would like to be able to use serial port terminal, or equivalent with Xubuntu so I can use my kpc3 packet terminal, connect to the com port on the back of my computer.

9 Answers 9

The tty devices belong to the «dialout» group, I suspect you are not a member of this group and hence are denied access to /dev/ttyS0, so you need to add yourself to that group.

First check if you are a member of that group:

..this will list all the groups you belong to. If you don’t belong to the dialout grup then add yourself to it, for example:

You then need to log out and log back in again for it to be effective. Then see if it fixes your problem.

The only solution that works for me is to: (every time I boot the machine)

It really needs to be fixed at time of installation. I’m on 15.10 and have tried 16.04 LTS, still the same there. Seems like such a simple fix.

The older versions 10.04LTS did not have this problem.

On Ubuntu 18.04, I fixed this issue with the following commands:

And after this, reboot.

If you still have issues, try to debug with:

And look for «denied» in the strace.

You can just use this command:

This will add the current user to the dialout group. Login and out it to take effect.

Had a look around various forums and it looks to be a bug related to permissions. Here’s how I got around the problem (long version). You WILL need BOTH cu and setserial packages installed.

In three terminal tabs, monitored output from # tail -f /var/log/messages That’s how we know if we have a /dev/ttyUSB0 or not.

In the second tab, simply ran a loop to ls -l this device to see it’s permissions and it’s group ID is ‘dialout’. THIS is the critical bit. For some reason, your user MUST use this GID to do the cu , so.

In the third tab, as root, did # newgrp dialout (to correspond with the GID of dialout). Tested with # touch /tmp/anything . doing ls -l on this file shows it is created by root with a dialout group, so we’re ready to . # cu -l /dev/ttyUSB0 In my case I needed to hit return again to see the expected prompt, in other cases speed may need to be specified.

Here is the solution:

I had just updated my operating system to Ubuntu 18. normally I would install arduino IDE through the Arduino web sight because the one provided via Ubuntu Software portal was always an older version, and I wanted the newest features and board support. However, since I just installed the newest operating system, I figured that the official software center from ubuntu would have the newest version of the IDE listed, and it did.

Now to the juicy part! Both my laptop and my desktop had the same problems accessing the serial ports. i had done the make user part of the dial-up group, and set permissions for the serial port, but always had to log out then back in, do it all again every time i rebooted! NOT FUN!.

This time, it didn’t work. Even in the software center the permissions option for the software shows the serial port «disconnected». no option to allow permission to the port even after all the permissions were granted manually through the terminal window using sudo.

I decided to uninstall the Arduino IDE from the software center, and install it from the web sight, so i did. This time I read the install files, just to see if it mentions permissions for the serial port or not, *****of course it did! ****** all the ports are set with full access permissions, user access across the board. Turns out this was the answer. after running the arduino-linux-setup.sh file provided by arduino, all serial port problems were solved. the following is an excerpt from the arduino-linux-setup.sh file;

so you see even the KERNEL is effected. My suggestion:

install from the arduino ide web site. ignore the software center at this time, until it is repaired. Yes the SOFTWARE CENTER is not allowing permmisions to the serial port during install, and forever after.

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