Serial Port configuration in RHEL

mrjj

@Nimika
Np. as far as I can see it's the same for Red Hat with ttySX access, so there is
tons on google on the topic on allowing user X to read and write to /dev/ttSxxx
stuff.
http://ithelpblog.com/os/linux/bashandscripts/howto-add-user-to-group-on-linux-redhat-rhel-centos-fedora/

Nimika

@SGaist Can I use serial ports to any user other than root?

mrjj

@Nimika
Hi
Any user can be granted access to /dev/X devices.
Often it is done via the dialout group as its already assigned to serial devices such as ttyS0 and
any user that is member of that group can use it.
so often
sudo adduser TheUserName dialout
and and reboot is all that is needed.
Adding user to group might have slightly different syntax on RH but concept and rights are 100% the same.:)
http://websistent.com/fix-serial-port-permission-denied-errors-linux/

Nimika

@mrjj Thanks let me try it.

jsulm

@mrjj @Nimika Just a note: after adding currently logged on user to a group you do not have to reboot (its not Windows :-)) - just log out and log in again.

Nimika

@jsulm Thank you!!
But still in my case maybe RHEL is not allowing any other user to add in dialout group.

mrjj

@Nimika said in Serial Port configuration in RHEL:

RHEL is not allowing any other user to add in dialout group.

cant you just use sudo in front?

jsulm

@Nimika RHEL works like any other Linux distribution. To add a user to a group you need to be root. You can either login as root, or just enter su in a terminal window enter your root password and then add the user to the group. su is used to become root in a shell (you need root password).
@mrjj I think on RHEL sudo is usually not used, so sudo will probably not work (as far as I know, I could be wrong as I use Ubuntu).

Nimika

@jsulm
Yeah I did all possibilities which I think can be done on RHEL.
By the way Thanks a lot for your all kind replies. :)

jsulm

@Nimika So, is your user now member of dialout group? You can check this executing "groups" command in a terminal (not as root but as the user who needs the access rights!). You can add a user to a group manually: open /etc/group file in an editor (as root), look for a line like "dialout:x:115:" and append user name at the end of that line.

SGaist

In addition to what my fellows already wrote, if you're not too found of manipulating your user setting with the command line, most of desktop environment (KDE, Gnome, etc.) provide user management software so you'll likely be able to add your user to the dialout group with them. They should ask for an admin password when required.

mrjj

@jsulm
Oh, you are right. it might not be set up at all
https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux_OpenStack_Platform/2/html/Getting_Started_Guide/ch02s03.html
so su is the way to go.

Nimika

@jsulm
No my user is not the member because its not working in the dialout group.
I did by editing to the group file as well. Whenever I am in my root and adding the user to the group it is showing that this user is already have the group.

@SGaist
which management software you are talking about??

mrjj

@Nimika
HI
I think the champion means that many newer distros have also a GUI version
to change user / groups versus using the command line. :)

jsulm

@Nimika Sorry, I don't understand. To add a user manually you open /etc/group file in a editor (you need to be root to edit this file). Look for the group "dialout" and append the username at the end of the line containing the group, like:

dialout:x:124:myuser

This is how it works on UNIX/Linux since decades.
"it is showing that this user is already have the group" - what/who is showing this?

So, here what you should do:

$ su
ENTER YOUR ROOT PASSWORD
$ vim /etc/group
APPEND USERNAME AT THE END OF THEdialout LINE
SAVE THE FILE
CLOSE vim

You can use another editor instead of vim.

Nimika

@mrjj
ok thank you. Let me check.

@jsulm
I mean the /etc/group file is already containing my user thats why terminal is showing the message.

jsulm

@Nimika Then this user should now have access. The user needs to log out and log in again after adding him to a group.
Does it work now?

Nimika

@jsulm
Sorry to say but still the same problem.

Buckwheat

Some admins do not like you to cross groups (Like US GOV admins). You can, however, get them to make a UDEV rule that will set the permissions when the port is found. This is especially useful if you need many users to access the port.

This is a more permanent solution than using rc.local to change port access modes as it will set the modes each time the port is plugged-in as well as when the computer is rebooted. Your admin should know how to do this. If you are the admin, there are plenty of technotes on adding rules to UDEV. You can even give the port a better, more consistent, name the ones the kernel provides as they can reorder at reboot, etc.

In ~~/etc/rules.d/my.rules~~ /etc/udev/rules.d

SUBSYSTEM=="tty", ENV{ID_PATH}=="pci-blah blah blah", MODE="0666", SYMLINK+="tty-my-device"

The "pci-blah blah blah" can be found using udevadm info /dev/tty<device>

Buckwheat

@Buckwheat Sorry, it is /etc/udev/rules.d