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Redirecting stdout to a file as a regular user using sudo and tee

Last Updated: [2023-03-29 Wed 07:06]

Sometimes you’ll have to pipe something to a file as root. However, you’ll find you’ll run into issues when running something like this: sudo echo "" > textfile.txt. Despite using the sudo command, you’ll get a permission denied error. This is because only the part of the command before the > is run through sudo, the output is being performed as your own user. Most people would get around this using the dreaded sudo su method. However, this is a better way:

echo "" | sudo tee textfile.txt > /dev/null

A little explanation is needed here.

Firstly we’re using echo to write nothing to the stdout. We’re then piping this to sudo which in turn is running tee as root to a file we’ve called “textfile.txt”. Finally, tee also, by default, prints what it’s doing back to stdout as it’s intended to push the same data to two places, so we’re redirecting that to /dev/null to keep the command silent.

The same method can be used to do MySQL dumps to a directory that is only readable by normal users:

sudo mysqldump --routines --single-transaction --quick --max_allowed_packet=1G --database production-data | sudo tee 2021-09-12-production-data-dump-with-routines.sql > /dev/null

In this example, redirecting tee's output to /dev/null is absolutely required it would have happily spat out the full 25GB MySQL Dump to stdout.

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