Peer authentication failed for user in postgresql - postgresql

Question

I am trying to run some postgresql commands through a fabric script. When I execute the script I get:
out: psql: FATAL: Peer authentication failed for user "sparc2"
This is how my pg_hba.conf file looks like:
# "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
# added
local sparc2 sparc2 md5
host sparc2 sparc2 127.0.0.1/32 md5
host sparc2 sparc2 10.0.2.2/32 md5
host all all all password
I have also modified the postgresql.conf file with adding this line:
listen_addresses = '*'
After applying the changes I restarted postgresql. But the error is still the same.

Answer 1

PostgreSQL has 2 connection entry points:
TCP/IP (host in pg_hba.conf)
Unix sockets (local in pg_hba.conf)
Your server is configured to use peer auth which works only for Unix sockets, and means - ask the kernel if the OS username matches DB username.
You have following options:
change pg_hba.conf to use md5 auth for local socket connections, or
change connection settings in your script to use IP connection (127.0.0.1 should work) instead of socket connection. [ This may not require editing the files - sometimes setting PGHOST variable is enough ], or
make your script to run from OS user sparc2, not postgres.
Risks / drawbacks
if you change peer to md5, some automation scripts that run from "postgres" OS user, and rely on "peer" auth, will stop working. They will start asking for password
if you change peer to md5, and forget database superuser password, you may have to re-enable peer auth to reset it.
In general, the "peer" auth is OK. Ease and security of kernel-based local auth is the reason why many distributions choose it for local admin connections. It is useful especially on multi-user shell servers. You can disable it for selected accounts only:
#CHANNEL DB USER METHOD
local all sparc2 md5
local all all peer
More details: here and here.