Unix script can't alter postgres hba.conf configuration file on Ubuntu

Question

I'm attempting to setup postgres 9.6 on ubuntu/vagrant through a provisioning script. Part of my script adds a line to pg_hba.conf with the following command:

sudo -u postgres echo "host all all all md5" >> /etc/postgresql/9.6/main/pg_hba.conf

However, this gives me the error -bash: /etc/postgresql/9.6/main/pg_hba.conf: Permission denied

Which is strange because I am allowed to edit the file with either sudo nano or sudo -u postgres nano.

Here are the permissions on the file: -rw-r----- 1 postgres postgres 4641 Apr 6 16:11 pg_hba.conf

How can I add this line to my configuration file in a script?

Your sudo is covering the echo, but not the >>. If you quote the whole thing, it should work better. — jmelesky
– jmelesky, Commented Apr 6, 2017 at 16:25
@MikeSherrill'CatRecall' that seems to work. Would you add an answer so that I can credit you? — Jacob Lyles
– Jacob Lyles, Commented Apr 6, 2017 at 16:31

Mike Sherrill 'Cat Recall' · Accepted Answer · 2017-04-06 16:52:52Z

1

The problem here is that redirection happens before command execution. So the redirection doesn't have the elevated privileges you expected it to.

There's more than one way around that problem. I generally use something like this.

echo "host..." | sudo tee -a /etc/postgresql/9.6/main/pg_hba.conf

Piping to sudo tee... avoids problems with quoting.

How bash executes commands

Redirections

edited Apr 6, 2017 at 16:52

answered Apr 6, 2017 at 16:46

Mike Sherrill 'Cat Recall'

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