使用 postgres 角色运行 psql 命令

Question

I am try to run psql command with postgres role.

(1) sudo psql -U postgres Since postgres differs from my OS username, I receive the Peer authentication failed for user "postgres" error when I run it.

(2) But when I run sudo -u postgres psql , it succeeds

My terminal image

I'm not sure how the (2) commands can work because, according to a Postgres document, peer authentication happens automatically locally and my current OS username is different from postgres . (I made no changes to pg_hba.config or pg_ident.config files.)

And what is the difference between the (1) and the (2) command?

Answer 1

In your first attempt, you used sudo to become the root user (because there was no -u option) and tried to connect as database user postgres , which will fail with peer authentication because root is different from postgres .

In your second attempt, you used sudo to become user postgres and called psql without specifying a username, so that the username defaults to the same as your current operating system user name, namely postgres . Then peer authentication works.