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I have a file /dev/ttyS0. And every time I boot, its file permissions are changed to default (unwritable) by the system. So, I have to run a chmod command every time I boot-up. How can I change its file permission permanently?

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  • What does it means "unwritable by the system"? Please show the output of ls -l /dev/ttyS0.
    – enzotib
    Dec 14, 2011 at 8:15
  • Why does this down vote? we use linux, isn't that mean we have freedom to set what chmod we want.
    – GusDeCooL
    May 9, 2013 at 19:46
  • @enzotib Every time reboot, the chmod back to 660
    – GusDeCooL
    May 9, 2013 at 19:47
  • Here may answer you question: askubuntu.com/questions/58119/…
    – GusDeCooL
    May 9, 2013 at 19:49
  • @GusDeCooL - Sure do what you want. Best thing abut open source, if you break it you get to keep both pieces.
    – Panther
    Apr 14, 2015 at 1:49

1 Answer 1

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Changing the file permission is not a good idea. I think /dev/ttyS* are designed to be accessed by user space applications, so you dont need to make it accessible to everybody. Instead you should give permission to use the serial ports to users that need access. If I am not wrong, you can do this by adding your user to the group uucp which can be done by running the following command in the terminal:

usermod -aG uucp <you_user_name> 

If this does not solve your issue, try posting a bit more details on what you are doing. What device are you accessing and explaining how are you writing to it, and perhaps providing some code snippets will help give more specific answer.

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