How do I allow non-root access to /ttyUSB0?

Question

Since I updated from Ubuntu 10.04 (Lucid Lynx) to Ubuntu 12.04 (Precise Pangolin), I am unable to access the device connected in /ttyUSB0 if I don't have root access.

To be more specific, I use a USB-to-serial com port converter to access and configure Cisco equipment with software called PuTTY. It happens that, since I upgraded to 12.04, PuTTY only sees the connected device when I run it as gksudo putty. If not, it says "unable to connect to port /ttyUSB0".

I have managed to change the permissions via chmod 666, and it works, but if I disconnect the USB device and reconnect, it goes back to root only. How do I permanently allow non-root access? I have a clue it might be via udev rules, but I have no idea how to do it.

Obs.: Manufacturer and drivers are "PROLIFIC"

Even with dialout group set up, PuTTY may only work with sudo if the font defaults to server:fixed so try setting this to Monospace before connecting — theSparky, Feb 01 '25 at 22:56

score 165 · Answer 1 · edited Oct 13 '22 at 10:45

165

The device is most likely attached to user group dialout.

To find out which user group the device is attached to:

stat /dev/ttyUSB0

This should produce something like

Gid: (   20/ dialout)

Just add your user to the dialout group so you have appropriate permissions on the device.

sudo usermod -a -G dialout $USER

(You may need to logout and back in for the new group to take effect.)

No need to mess around with permissions or udev rules.

edited Oct 13 '22 at 10:45

beauxq

211
4
13

answered May 07 '12 at 14:32

Rinzwind

310,127

3

no success... still no acces to ttyUSB0 without root... any other ideas??? – yurividal May 11 '12 at 16:16
Great, works fine for me.. thanks! sudo usermod -a -G dialout pier – lppier Sep 02 '14 at 02:51
1

@tom-hennen I guess you should add it first as a comment rather than edit it directly. – MadMike Oct 29 '14 at 13:33
3

This doesn't work for Debian – Mike May 16 '15 at 16:51
@mike that is why we do not support debian ;) and in 2012 this did work for Ubuntu. – Rinzwind May 16 '15 at 17:20
@Rinzwind It was just a comment. I wasn't complaining or anything. – Mike May 16 '15 at 17:23
This worked perfect for me using Linux Mint, thanks! – Nate Oct 02 '16 at 05:52
2

Kudos for including "may need to logout and back in". – Rob Stoecklein Jul 26 '18 at 13:57
4

In Ubuntu (I'm on 18.04), logout/login doesn't work. we have to reboot after doing usermod. – Sujay Phadke Mar 02 '19 at 06:42
1

Using newgrp dialout is enough to test the new permission in a shell, without having to logout. – Tey' Mar 19 '20 at 16:35
With Kali linux after that I can only read from serial port, but not write. – ltWolfik Dec 23 '21 at 15:11
UPD: The problem was - for another user (non-root) the minicom was set up incorrectly. – ltWolfik Dec 23 '21 at 15:28
For some reason this didnt work for me... I'm on Ubuntu 22.04. What i did was a crontab that runs every minute that does the command chmod 777 /dev/ttyS0 ... – Raul Chiarella May 11 '22 at 14:09
1

@RaulChiarella no please no. ANYONE even from the outside could address this device. If the owner is not dialout change my command to what group is is; the method I posted -must- work cuz that is how groups work. If you do stick to chmod do 770 never 777. – Rinzwind May 11 '22 at 18:30
Oh... But there is'nt anything i can do, besides, the system doesnt connect at all to the internet. Its a local system only that uses only local connection to connnect to local servers... – Raul Chiarella May 11 '22 at 23:44
This answer should show up when googling for 'FTDI ubuntu not working', or 'FTDI ubuntu permission denied'. Would have saved me an hour :). – bas Sep 01 '22 at 18:52
The answer would be better if it included a way to check to see what user group the device is attached to. – beauxq Oct 12 '22 at 18:11

score 16 · Accepted Answer · edited Jun 25 '12 at 03:02

16

It's possible this is related to modemmanager, as detailed here.

I removed that (sudo apt-get remove modemmanager) and it fixed my problem.

You still need to be in the dialout group though.

edited Jun 25 '12 at 03:02

Eliah Kagan

119,820

answered Jun 24 '12 at 12:26

Ed.

176

2

What if I can't remove modemmanager? I have a friend that has a 3G modem, and it seems he can't remove modemmanager because of that. How can he access /ttyUSB0 on 12.04 without root, but without removing modemmanager? – Leonardo Montenegro Jul 19 '13 at 12:22
You can try by stopping it? sudo stop modemmanager It worked for me. – Aleks Aug 12 '14 at 09:19
Been a few years, but this is still the case in Ubuntu 17.10. Had to do a sudo apt-get purge modemmanager before sudo usermod -a -G dialout $USER had the desired effect. – Stéphane Nov 06 '17 at 03:29
2

Please note: being in dialout group is sufficient if you do not use modemmanager in any way. The modemmanager removal is very case-specific to OPs situation, and is not a requirement every time. – Sergiy Kolodyazhnyy Dec 15 '19 at 01:44
Thank you bro. That solved my problem. I got access denied fron non-root user while the permission of /dev/ttyUSB0 was 777 ! – SuB Aug 01 '21 at 07:29

score 15 · Answer 3 · edited Feb 12 '13 at 11:10

15

sudo adduser <the user you want to add> dialout
sudo reboot

Mentioned by "Try now" worked for me. Check that You have dialout as group for ttyUSB0:

ls -l /dev/ttyUSB0

in my case the output is:

crw-rw---T 1 root dialout 188, 0 Feb 12 12:01 /dev/ttyUSB0

edited Feb 12 '13 at 11:10

Aditya

13,626

answered Feb 12 '13 at 10:25

user130451

159

in Linux Mint 18 Cinnamon I get this error when calling ' ls -l /dev/ttyUSB0 ' ls: cannot access '/dev/ttyUSB0': No such file or directory – flyingdrifter Dec 08 '16 at 22:56

score 5 · Answer 4 · edited Apr 13 '17 at 12:24

5

As reported by Rinzwind, start by typing:

sudo usermod -a -G dialout $USER

But that is only part of the solution, as then you must reboot the system:

sudo reboot

edited Apr 13 '17 at 12:24

Community

1

answered Sep 11 '14 at 11:55

lboz

51

8
Please don't post comments as answers. 2) No need to reboot; just log out and log back in.

gertvdijk

Sep 11 '14 at 12:07

3

I had to reboot to get this to work. A Logoff didn't propagate the change. – user1182988 Jun 03 '19 at 20:19

score 3 · Answer 5 · edited Sep 11 '12 at 05:40

3

This worked for me. Just press Ctrl+Alt+T on your keyboard to open Terminal. When it opens, run the command below.

sudo adduser <the user you want to add> dialout
sudo reboot
id -Gn

Try now.

edited Sep 11 '12 at 05:40

Mitch

109,937

answered Sep 10 '12 at 16:16

user88742

31

score 3 · Answer 6 · edited Oct 09 '14 at 10:17

3

I tried both

sudo usermod -a -G dialout $USER #(worked perfectly)

And sudo chmod 666 /dev/ttyUSB0 (worked but had to type the command again)

I also removed the mode manager but did not really help. Therefore, the best command that worked for me was

sudo usermod -a -G dialout $USER

edited Oct 09 '14 at 10:17

αғsнιη

36,400

answered Oct 09 '14 at 08:45

Salah Amean

31

score 1 · Answer 7 · answered Jul 30 '18 at 21:54

1

On Ubuntu 18.04 I had to add myself to the tty group.

I got hinted by the minicom command output:

minicom  /dev/ttyUSB0
minicom: cannot open /dev/tty8: Permission denied


ls -la /dev/tty8
crw--w---- 1 root tty 4, 8 juil. 31 08:27 /dev/tty

answered Jul 30 '18 at 21:54

Laurent

666

@PeterMortensen Because in this particular situation minicom application also opens /dev/tty8 which is handled by entirely different group than dialout. Issue isn't directly related to /dev/ttyUSB0 in this particular scenario and adding to dialout group won't fix the problem. But it does prevent one from using /dev/ttyUSB0 , hence it is one of the possible answers to the question – Sergiy Kolodyazhnyy Dec 15 '19 at 01:47
Checking the group associated to /dev/ttyUSB0 (group uucp on Arch Linux) and adding my user to that group was the solution for me. Thanks. – Paolo M Jul 01 '20 at 08:22

score -1 · Answer 8 · answered May 13 '19 at 12:15

-1

On Ubuntu 18.04:

sudo adduser <user> dialout
Full reboot, for some reason mere logout/login is not sufficient (bug report.).

answered May 13 '19 at 12:15

Eero Aaltonen

1,434

score -1 · Answer 9 · answered Sep 04 '16 at 18:16

-1

I had this problem with /dev/ttyS0 in Mint Rosa. Adding the user to the dialout group is required but in my case the device access was restricted and I had to expand it to give r/w access to group level also.

answered Sep 04 '16 at 18:16

LesA

1

1

Welcome to Ask Ubuntu! I recommend [edit]ing this answer to expand it with specific details about how to do this. (See also How do I write a good answer? for general advice about what sorts of answers are considered most valuable on Ask Ubuntu.) – David Foerster Sep 04 '16 at 18:42

score -5 · Answer 10 · edited Jan 16 '14 at 23:30

-5

navigate to /etc/ folder and edit the group file add your username like this dialout:x:20:USER

worked perfect for me :)

edited Jan 16 '14 at 23:30

chaos

28,256

answered Jan 16 '14 at 22:57

Bane

1

5

It is generally considered bad practice to edit these files directly as some simple mistakes can cause loss of access. – flickerfly Apr 10 '15 at 20:49

How do I allow non-root access to /ttyUSB0?

10 Answers10