Postgres user does not exist?

I have just installed Postgres and have been tinkering with it and various configurations for 1-2 hours.

I am stuck on being unable to change to the postgres-user

$ su - postgres yields the following error: su: unknown login: postgres

$ sudo -u postgres psql yields the following error: sudo: unknown user: postgres

These attempts are made as the normal user. Trying them as root has the exact same results. I have installed postgres via Homebrew on OS X, and I have read the instructions multple times.

psql: Logs me in with my default username

psql -U postgres: Logs me in as the postgres user

Sudo doesn't seem to be required for me.

I use Postgres.app for my OS X postgres database. It removed the headache of making sure the installation was working and the database server was launched properly. Check it out here: http://postgresapp.com

Edit: Credit to @Erwin Brandstetter for correcting my use of the arguments.

By psql --help, when you didn't set options for database name (without -d option) it would be your username, if you didn't do -U, the database username would be your username too, etc.

But by initdb (to create the first database) command it doesn't have your username as any database name. It has a database named postgres. The first database is always created by the initdb command when the data storage area is initialized. This database is called postgres.

So if you don't have another database named your username, you need to do psql -d postgres for psql command to work. And it seems it gives -d option by default, psql postgres also works.

If you have created another database names the same to your username, (it should be done with createdb) then you may command psql only. And it seems the first database user name sets as your machine username by brew.

psql -d <first database name> -U <first database user name>

or,

psql -d postgres -U <your machine username>
psql -d postgres

would work by default.

OS X tends to prefix the system account names with "_"; you don't say what version of OS X you're using, but at least in 10.8 and 10.9 the _postgres user exists in a default install. Note that you won't be able to su to this account (except as root), since it doesn't have a password. sudo -u _postgres, on the other hand, should work fine.

the discussion and answer here was massively helpful to me:

https://stackoverflow.com/questions/17633422/psql-fatal-database-user-does-not-exist

psql -U postgres

Worked fine for me in case of db name: postgres & username: postgres. So you do not need to write sudo.

And in the case other db, you may try

psql -U yourdb postgres

As it is given in Postgres help:

psql [OPTION]... [DBNAME [USERNAME]]

I get exactly the same errors as kryshah with su - postgres and sudo -u postgres psql. DanielM's answer gives also errors.

Outputs when wrong settings

Answer however from przbabu's comment.

masi$ psql
psql: FATAL:  database "masi" does not exist
masi$ psql -U postgres
psql: FATAL:  role "postgres" does not exist
masi$ psql postgres
psql (9.4.1)
Type "help" for help.

I think the some part of this problem may be in owner settings in OSX

masi$ ls -al /Users/
total 0
drwxr-xr-x   7 root      admin  238 Jul  3 09:50 .
drwxr-xr-x  37 root      wheel 1326 Jul  2 19:02 ..
-rw-r--r--   1 root      wheel    0 Sep 10  2014 .localized
drwxrwxrwt   7 root      wheel  238 Apr  9 19:49 Shared
drwxr-xr-x   2 root      admin   68 Jul  3 09:50 postgres
drwxr-xr-x+ 71 masi      staff 2414 Jul  3 09:50 masi

but doing sudo chown -R postgres:staff /Users/postgres gives chown: invalid user: ‘postgres:staff’.

In short, this is not the solution the problem. Use the tools provided by the postgres installation to create a user and database.

To get right settings and outputs

There are specific commands after postgres installation to add a new user to the database system. After initdb, run the following as described here

createuser --pwprompt postgres
createdb -Opostgres -Eutf8 masi_development
psql -U postgres -W masi_development

To avoid the password request all the time, you have three choices as described here.

For me This was the solution on macOS ReInstall the psql

brew install postgres

Start PostgreSQL server

pg_ctl -D /usr/local/var/postgres start

Initialize DB

initdb /usr/local/var/postgres

If this command throws an error the rm the old database file and re-run the above command

rm -r /usr/local/var/postgres

Create a new database

createdb postgres_test
psql -W postegres_test

You will be logged into this db and can create a user in here to login

The solution is simple:
log in as root
and after:

su - postgres

psql