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
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?
CodePudding user response：
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.