Ошибка peer authentication failed for user postgres

pg_config is for compliation information, to help extensions and client programs compile and link against PostgreSQL. It knows nothing about the active PostgreSQL instance(s) on the machine, only the binaries.

pg_hba.conf can appear in many other places depending on how Pg was installed. The standard location is pg_hba.conf within the data_directory of the database (which could be in /home, /var/lib/pgsql, /var/lib/postgresql/[version]/, /opt/postgres/, etc etc etc) but users and packagers can put it wherever they like. Unfortunately.

The only valid ways find pg_hba.conf is to ask a running PostgreSQL instance where it’s pg_hba.conf is, or ask the sysadmin where it is. You can’t even rely on asking where the datadir is and parsing postgresql.conf because an init script might passed a param like -c hba_file=/some/other/path when starting Pg.

What you want to do is ask PostgreSQL:

SHOW hba_file;

This command must be run on a superuser session, so for shell scripting you might write something like:

psql -t -P format=unaligned -c 'show hba_file';

and set the environment variables PGUSER, PGDATABASE, etc to ensure that the connection is right.

Yes, this is somewhat of a chicken-and-egg problem, in that if the user can’t connect (say, after screwing up editing pg_hba.conf) you can’t find pg_hba.conf in order to fix it.

Another option is to look at the ps command’s output and see if the postmaster data directory argument -D is visible there, e.g.

ps aux  | grep 'postgres *-D'

since pg_hba.conf will be inside the data directory (unless you’re on Debian/Ubuntu or some derivative and using their packages).

If you’re targeting specifically Ubuntu systems with PostgreSQL installed from Debian/Ubuntu packages it gets a little easier. You don’t have to deal with hand-compiled-from-source Pg that someone’s initdb’d a datadir for in their home dir, or an EnterpriseDB Pg install in /opt, etc. You can ask pg_wrapper, the Debian/Ubuntu multi-version Pg manager, where PostgreSQL is using the pg_lsclusters command from pg_wrapper.

If you can’t connect (Pg isn’t running, or you need to edit pg_hba.conf to connect) you’ll have to search the system for pg_hba.conf files. On Mac and Linux something like sudo find / -type f -name pg_hba.conf will do. Then check the PG_VERSION file in the same directory to make sure it’s the right PostgreSQL version if you have more than one. (If pg_hba.conf is in /etc/, ignore this, it’s the parent directory name instead). If you have more than one data directory for the same PostgreSQL version you’ll have to look at database size, check the command line of the running postgres from ps to see if it’s data directory -D argument matches where you’re editing, etc.
https://askubuntu.com/questions/256534/how-do-i-find-the-path-to-pg-hba-conf-from-the-shell/256711

In this document I am going to discuss about some of the most frequent errors faced by users while connecting to PostgreSQL. This is document is to help the beginners who started working on PostgreSQL. PostgreSQL has a process called postmaster which acts as listener process, by default the process listens on 5432.

There are different tools available to connect to PostgreSQL, here I am going to use the psql command line tool but there is no difference in error messages.

ERROR – 1

[root@localhost ~]# psql
psql: error: FATAL: role “root” does not exist

By default “psql” command line tool use the operating system user as the database user and localhost the hostname if the user name is not passed as argument, here I logged in as the root user and tried to login to PostgreSQL without username which caused the error.

Solution

give the username when logging into the database, by default the psql command line take the username as the database name, so no need to pass the database as I am trying to connect to PostgreSQL.

psql -U postgres -h localhost

ERROR – 2

[root@localhost ~]# psql -U postgres
psql: error: FATAL: Peer authentication failed for user “postgres”

Solution

By default PostgreSQL installation using yum repository configure the pg_hba.conf with peer, ident authentication. So change the peer and ident authentication methods to md5 and reload the configuration.

[root@localhost data]# psql -U postgres
Password for user postgres: 
psql (12.5)
Type "help" for help.

postgres=# 

ERROR – 3

[root@localhost data]# psql -h 192.168.159.151 -U postgres -d postgres
psql: error: could not connect to server: Connection refused
Is the server running on host “192.168.159.151” and accepting
TCP/IP connections on port 5432?

This is the common error users get when they connect to PostgreSQL. The error represents there is no listener for host and port combination.

Solution

Most common issue is listener_address parameter is set to ‘localhost’ or port set to a non default value.

postgres=# show listen_addresses ;
 listen_addresses 
------------------
 localhost
(1 row)

postgres=# show port;
 port 
------
 5432
(1 row)

Here the issue is listener_address is localhost, so changed it to ‘*’ where it listens on all ip’s in my host. I have only one ip configured, if your server has multiple ip’s then set the ip address on which the PostgreSQL connections should happen.

Configure the listener_address or change the port and restart the PostgreSQL cluster.

postgres=# alter system set listen_addresses to '*';
ALTER SYSTEM
postgres=# q
-bash-4.2$ /usr/pgsql-12/bin/pg_ctl -D /var/lib/pgsql/project/data restart
waiting for server to shut down.... done
server stopped
waiting for server to start....2020-12-20 07:12:20.317 PST [3051] LOG:  starting PostgreSQL 12.5 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-39), 64-bit
2020-12-20 07:12:20.318 PST [3051] LOG:  listening on IPv4 address "0.0.0.0", port 5432
2020-12-20 07:12:20.318 PST [3051] LOG:  listening on IPv6 address "::", port 5432
2020-12-20 07:12:20.319 PST [3051] LOG:  listening on Unix socket "/var/run/postgresql/.s.PGSQL.5432"
2020-12-20 07:12:20.320 PST [3051] LOG:  listening on Unix socket "/tmp/.s.PGSQL.5432"
2020-12-20 07:12:20.332 PST [3051] LOG:  redirecting log output to logging collector process
2020-12-20 07:12:20.332 PST [3051] HINT:  Future log output will appear in directory "log".
 done
server started

ERROR – 4

-bash-4.2$ psql -h 192.168.159.151 -U postgres -d postgres
psql: error: FATAL: no pg_hba.conf entry for host “192.168.159.151”, user “postgres”, database “postgres”, SSL off

This is another common error which users will face due to missing entry for the user host address (ip address) in pg_hba.conf file. host based authentication file presents in data directory which has a list of ip addresses or host addresses allowed to connect to PostgreSQL.

Solution

Make an entry like below for the user host or subnet in pg_hba.conf file. Any ip address with 192.168.X.X will be able to connect to the host.

host	all		all		192.168.0.0/16		md5

ERROR – 5

-bash-4.2$ psql -h 192.168.159.151 -U postgres -d postgres
psql: error: FATAL: sorry, too many clients already

-bash-4.2$ psql -h 192.168.159.151 -U viswamitra -d postgres
psql: error: FATAL: remaining connection slots are reserved for non-replication superuser connections

-bash-4.2$ psql -U viswamitra -d postgres -h 192.168.159.151
psql: error: FATAL: too many connections for role “viswamitra”

This is also a common error users face after started using the database in application. This errors will come after the connection limit is reached to the maximum configured value.

Connection limit can be set at different levels

1. cluster – which is applicable for all users and databases
2. user – which is applicable for the user
3. database – which is applicable for the given database

Solution

Login to the database as a super user, if there are any idle connections from longer time close them and check the application connection pool settings to close the idle connections after some time interval.

postgres=# select pid,datname,usename,application_name,state,now()-state_change as idle_duration from pg_stat_activity where state = 'idle';
 pid  | datname  |  usename   | application_name | state |  idle_duration  
------+----------+------------+------------------+-------+-----------------
 3656 | alex     | postgres   | psql             | idle  | 00:14:06.647055
 3652 | alex     | postgres   | psql             | idle  | 00:14:11.718486
 3623 | postgres | viswamitra | psql             | idle  | 00:15:47.530912
(3 rows)

postgres=# select pg_terminate_backend(3656);
 pg_terminate_backend 
----------------------
 t
(1 row)

If there are no idle sessions to cancel and the error is first and second one in the list increase the “max_connections” in postgresql.conf file. This requires a reboot of the PostgreSQL cluster to make it effect.

postgres=# alter system set max_connections to '1000';
ALTER SYSTEM
postgres=# 

/usr/pgsql-12/bin/pg_ctl -D /var/lib/pgsql/project/data restart

For third error (5.3) , the connection limit is configured at the user level, it can be changed using the alter user statement.

postgres=# alter user viswamitra connection limit 100;
ALTER ROLE