在postgres中创建数据库时出错

Question

I want to create user and database in linux server. I am able to create user with the following code:

su - postgres
# createuser -S -D -R myUser

but when I tried to create database with code :

# createdb -U myUser -p 5432 myDatabase

I get following error:

createdb: could not connect to database postgres: FATAL:  Ident authentication failed for user "myUser"

I am new to linux so I am unable to figure out why I was able to create user but while creating database there is connection error with postgres. And also error for ident authentication for user.

Answer 1

I am new to linux so I am unable to figure out why I was able to create user but while creating database there is connection error with postgres. And also error for ident authentication for user.

ident is an authentication schema that relies on the currently logged in user. If you've su -s to postgres and then try to login as another user, ident will fail (as it's not the currently logged in user). You can solve this issue in two ways, I tend to use the latter.

solution : simply make sure the currently logged in user is the user with which you would like to log in to postgres:

postgres@machine:~$ createuser -S -D -R myUser
postgres@machine:~$ exit
machine:~# su - myUser
myUser@machine:~$ psql myDatabase

better solution : change pg_hba.conf (probably located in /etc/postgresql/8.4/main/ or similar), and make sure you add the "md5" authentication schema to the list of options. Here's my pg_hba.conf on my development box, without comments:

berry@berry-pc:~$ sudo cat /etc/postgresql/8.4/main/pg_hba.conf | grep -v "^#" | grep -v "^$"
local   all         postgres                          ident
local   all         all                               md5
host    all         all         127.0.0.1/32          md5
host    all         all         ::1/128               md5

This tells PostgreSQL that postgres can login with ident , and all other users can login using the md5 authentication. That way, you can use the -U switch to the psql binary to denote which user you wish to become, so this actually works:

berry@berry-pc:~$ psql -U myUser myDatabase.

That said, I tend to use the postgres superuser to create databases. I then grant permissions on the newly created database to the newly created user, as such:

postgres@debian:~$ psql template1
template1=# CREATE USER myUser WITH PASSWORD 'myPassword';
CREATE ROLE
template1=# CREATE DATABASE myDatabase;
CREATE DATABASE
template1=# GRANT ALL PRIVILEGES ON DATABASE myDatabase TO myUser;
GRANT
template1=# \q

Hope that helps.

ADDENDUM : Once you've altered the pg_hba.conf, you will have to restart the PostgreSQL server to make sure it reads the configuration again. You can do so by issuing this command:

root@debian:~$ /etc/init.d/postgresql-8.4 restart

The script might be called "postgresql" instead of "postgresql-8.4", depending on OS and method of installation.

Answer 2

See for example: this link

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