pg_dump: [archiver (db)] connection to database failed: FATAL: Peer authentication failed for user "postgres"

I'm trying to backup my Postgres DB to another server but I keep getting denied access.

my pg_hba.conf file looks like this:

# DO NOT DISABLE!
# If you change this first entry you will need to make sure that the
# database superuser can access the database using some other method.
# Noninteractive access to all databases is required during automatic
# maintenance (custom daily cronjobs, replication, and similar tasks).
#
# Database administrative login by Unix domain socket
local   all             postgres                                peer

# TYPE  DATABASE        USER            ADDRESS                 METHOD

# "local" is for Unix domain socket connections only
local   all             all                                     peer
# IPv4 local connections:
host    all             all             127.0.0.1/32            md5
# IPv6 local connections:
host    all             all             ::1/128                 md5
# Allow replication connections from localhost, by a user with the
# replication privilege.
#local   replication     postgres                                peer
#host    replication     postgres        127.0.0.1/32            md5
#host    replication     postgres        ::1/128                 md5

If I change the postgres setting from PEER to TRUST, i can backup the code but the web site can no longer access the database (something about SSL error, which I know isn't the issue).

When I leave it as is, PEER, the server works - php can access the db - but I get error while trying to run the backup:

root> pg_dump -U postgres tablename > test.sql

.pg_dump: [archiver (db)] connection to database "tablename" failed: FATAL: Peer authentication failed for user "postgres".

PHP Apache Web site uses appropriate username and password.

Backup script looks like this: pg_dump -U postgres tablename > test.sql

how can I satisfy both the web site and the backup script so I can run both?

Entire script attempted is this: ssh SERVER "pg_dump -U postgres tablename| gzip -c" > /backup/sqlbackup.sql.gz

taken from Server Fault: ssh remote command-fu

Solution 1:

If your PHP Apache web site works with peer, keep this, and let's deal with it.

1. First Method :

As authentication is peer based, you have to specify the hostname (usually localhost) using -h option :

ssh server "pg_dump -h localhost -U postgres | gzip -c" >/backup/sqlbackup.sql.gz

The main issue here is that you will be prompted for the postgres user password. It is a problem for backups automation .

You can refer to this to avoid to be prompted for the password. But i will describe :

1. Create an hidden file named .pgpass in $HOME
2. Perform a chmod 600 .pgpass
3. Edit file .pgpass and add this line : localhost:5432:postgres:postgres:password

2. Second Method :

You could add a specific role for backups and trust it.

Create the backup role in Postgres :

CREATE ROLE backup WITH LOGIN SUPERUSER PASSWORD 'password'

Edit file pg_hba.conf, add role backup and trust it :

# Database administrative login by Unix domain socket
local   all             postgres                                peer
local   all             backup                                  trust

Restart postgresql

Then you should be able to run backup with the following :

ssh server "pg_dump -U backup postgres | gzip -c" >/backup/sqlbackup.sql.gz