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I am creating a small bash script to automate some simple tasks to handle my docker container. One of the commands I have is to clear the logs, but this doesnt work responding with "Permission denied".

The issue with this is I am using sudo.

if [ $CLEAR_OPT == true ]
then
  DOCKER_LOG_PATH=$(docker inspect $DOCKER_ID --format='{{.LogPath}}')
  sudo :> $DOCKER_LOG_PATH;
  exit 0
fi

This errors out.

However this following sequence of linux commands will not error out:

sudo -s
:> /var/lib/docker/containers/path/path-json.log

I tested without using sudo -s and it still didnt work in linux terminal.

Is there something I am missing? I thought when doing sudo it would run the command as root user?

Cyrus
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Killian Fortman
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1 Answers1

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The second line of your "working" example is executed in a new shell that already runs with root privileges, since sudo -s starts a new shell.

But the :> in your shell script will be executed by the shell and not by sudo, so it will run with the original (presumably lower) privileges.

The workaround is to pipe the output of something like echo to a command using sudo: echo | sudo tee "$DOCKER_LOG_PATH".

An even simpler and more explicit solution is to use a command that's explicitly built to truncate files: sudo truncate -s0 "$DOCKER_LOG_PATH".

Joachim Sauer
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