Agfdhyk

When connecting to postgres from command line, don't forget to add -h localhost as command line parameter. If not, postgres will try to connect using PEER authentication mode.

The below shows a reset of the password, a failed login with PEER authentication and a successful login using a TCP connection.

# sudo -u postgres psql

could not change directory to "/root"

psql (9.1.11)

Type "help" for help.



postgres=# password

Enter new password:

Enter it again:

postgres=# q

Failing:

# psql -U postgres -W

Password for user postgres:

psql: FATAL:  Peer authentication failed for user "postgres"

Working with -h localhost:

# psql -U postgres -W  -h localhost

Password for user postgres:

psql (9.1.11)

SSL connection (cipher: DHE-RSA-AES256-SHA, bits: 256)

Type "help" for help.



postgres=#

The pg_hba.conf (C:Program FilesPostgreSQL9.3data) file has changed since these answers were given. What worked for me, in Windows, is to open the file and change the METHOD from md5 to trust:

# TYPE  DATABASE        USER            ADDRESS                 METHOD



# IPv4 local connections:

host    all             all             127.0.0.1/32            trust

# IPv6 local connections:

host    all             all             ::1/128                 trust

Then, using pgAdmin III, I logged in using no password and changed user postgres' password by going to File -> Change Password

Just a note, on Linux You can simply run sudo su - postgres to become the postgres user and from there change what required using psql.

If you are in windows you can just run

net user postgres postgres

and login in postgres with postgres/postgres as user/password

For Windows installation, a Windows user is created. And "psql" use this user for connection to the port. If you change the PostgreSQL user's password, it won't change the Windows one.
The commandline juste below works only if you have access to commandline.

Instead you could use Windows GUI application "c:Windowssystem32lusrmgr.exe". This app manage users created by Windows. So you can now modify the password.

1. 
   

   Edit the file /etc/postgresql/<version>/main/pg_hba.conf and find the following line:

   
   
   

   local   all             postgres                                md5
   
   

   
   



2. Edit the line and change md5 at the end to trust and save the file



3. 
   

   Reload the postgresql service

   
   
   

   $ sudo service postgresql reload
   
   

   
   


4. 
   

   This will load the configuration files. Now you can modify the postgres user by logging into the psql shell

   
   
   

   $ psql -U postgres
   
   

   
   


5. 
   

   Update the postgres user's password

   
   
   

   alter user postgres with password 'secure-passwd-here';
   
   

   
   



6. Edit the file /etc/postgresql/<version>/main/pg_hba.conf and change trust back to md5 and save the file



7. 
   

   Reload the postgresql service

   
   
   

   $ sudo service postgresql reload
   
   

   
   


8. 
   

   Verify that the password change is working

   
   
   

   $ psql -U postgres -W
   
   

   
   

What I did to resolve the same problem was:

Open pg_hba.conf file with gedit editor from the terminal:

sudo gedit /etc/postgresql/9.5/main/pg_hba.conf

It will ask for password. Enter your admin login password.
This will open gedit with the file. Paste the following line:

host  all   all  127.0.0.1/32  trust

just below -

# Database administrative login by Unix domain socket

Save and close it.
Close the terminal and open it again and run this command:

psql -U postgres

You will now enter the psql console.
Now change the password by entering this:

ALTER USER [your prefered user name] with password '[desired password]';

If it says user does not exist then instead of ALTER use CREATE.

Lastly, remove that certain line you pasted in pg_hba and save it.

Adding the answer for Windows User for the latest postgres version (>10),

Go to your postgres installation location, and search for pg_hba.conf,
you will find it in ..postgresdatapg_hba.conf

Open that file with notepad, find this line,

# TYPE  DATABASE        USER            ADDRESS                 METHOD



# IPv4 local connections: 

host    all             all             127.0.0.1/32            md5

# IPv6 local connections:

host    all             all             ::1/128                 md5

#..

Change the method from md5 to trust,

# TYPE  DATABASE        USER            ADDRESS                 METHOD



# IPv4 local connections: 

host    all             all             127.0.0.1/32            trust

# IPv6 local connections:

host    all             all             ::1/128                 trust

# ...

Now go to your SQL Shell(PSQL) and leave everything blank,

Server [localhost]:

Database [postgres]:

Port [8000]:

Username [postgres]: 

It will not ask for password this time, and you will be logged in,

Now run this line,
ALTER USER yourusername WITH SUPERUSER

Now you can leave the shell with q

Again go to the file pg_hba.conf and change METHOD from trust to md5 again, and save it.

Now login with your new user and password and you can check du for its attributes.

The file .pgpass in a user's home directory or the file referenced by PGPASSFILE can contain passwords to be used if the connection requires a password (and no password has been specified otherwise). On Microsoft Windows the file is named %APPDATA%postgresqlpgpass.conf (where %APPDATA% refers to the Application Data subdirectory in the user's profile).

This file should contain lines of the following format:

hostname:port:database:username:password

(You can add a reminder comment to the file by copying the line above and preceding it with #.) Each of the first four fields can be a literal value, or *, which matches anything. The password field from the first line that matches the current connection parameters will be used. (Therefore, put more-specific entries first when you are using wildcards.) If an entry needs to contain : or , escape this character with . A host name of localhost matches both TCP (host name localhost) and Unix domain socket (pghost empty or the default socket directory) connections coming from the local machine. In a standby server, a database name of replication matches streaming replication connections made to the master server. The database field is of limited usefulness because users have the same password for all databases in the same cluster.

On Unix systems, the permissions on .pgpass must disallow any access to world or group; achieve this by the command chmod 0600 ~/.pgpass. If the permissions are less strict than this, the file will be ignored. On Microsoft Windows, it is assumed that the file is stored in a directory that is secure, so no special permissions check is made.

This is what worked for me on windows:

Edit the pg_hba.conf file locates at C:Program FilesPostgreSQL9.3data.

# IPv4 local connections:
host all all 127.0.0.1/32 trust

Change the method from trust to md5 and restart the postgres service on windows.

After that, you can login using postgres user without password by using pgadmin. You can change password using File->Change password.

If postgres user does not have superuser privileges , then you cannot change the password. In this case , login with another user(pgsql)with superuser access and provide privileges to other users by right clicking on users and selecting properties->Role privileges.