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linuxdockerterminaldebiantty

-su: /dev/tty: No such device or address

could please someone explain to me why this happens?

# su - someone -s /bin/bash -c "ls -la /dev/tty"
crw-rw-rw- 1 nobody nogroup 5, 0 Dec  7 20:53 /dev/tty
# BUT:
# su - someone -s /bin/bash -c "echo hello > /dev/tty"
-su: /dev/tty: No such device or address

I'm trieng to build a docker Container which has two services inside. Those services a startet by a Shell-Script:

CMD ["./starter.sh"]

Withing the Dockerfile I have redirected the Logs to /dev/stderr or /dev/tty

# None of the following works:
RUN ln -sf /dev/tty /var/log/thelog.log
RUN ln -sf /dev/stdout /var/log/thelog.log
RUN ln -sf /dev/stderr /var/log/thelog.log

The problem is that I'm trying to run one of the services as not root (su - someone -c "service"), which give's the following error:

unable to open log file [/var/log/thelog.log]: [6] No such device or address

How could I solve this problem? I want the logs to be linked to /dev/* AND want to run the User as non-root. Also I tried to add the User to the group tty, which did not work out.

Thanks.

Solution

  • The manpage for su states that the executed command will have no controlling terminal. Any writes to /dev/tty will return the ENXIO error: 

    $ errno ENXIO
ENXIO 6 No such device or address

    sudo does allocate a controlling terminal:

    sudo -u someone /bin/bash -c "echo hello > /dev/tty"

    There's no need for you to make a symbolic link to /dev/tty (/dev/stdout and /dev/stderr is enough) or use sudo if you use the USER directive in the Dockerfile or supervisor.