It's peer, Not ident

I needed a database on Ubuntu, settled on PostgreSQL among the SQL options, and went looking for how to install and use it. That’s how I saved a write-up covering everything from installation to getting into the prompt. Install with apt, check the processes, work out why psql won’t connect — a shape that’s easy to follow the first time through.

It’s from November 2021. Four years and ten months. Checking it turned up two kinds of problem: what drifted with time, and what was off from the start. The second kind matters more.

Table of contents

The version this guide gets you

The write-up targets Ubuntu 20.04. The install log includes this line:

Success. You can now start the database server using:

**pg_ctlcluster 12 main start**

The process check prints the path as /usr/lib/postgresql/12/bin/postgres too. PostgreSQL 12. Ubuntu pins one version per release and supports only that one for the life of the release.

PostgreSQL 12 reached end of life on November 21, 2024. Ubuntu 20.04’s standard support ended in May 2025 and it’s now in Ubuntu Pro’s ESM window. Both halves of the combination the write-up assumes have passed.

The more urgent line is the one below it. PostgreSQL 14, the default on Ubuntu 22.04, ends on November 12, 2026 — two months from now. If you’re running the distribution package on 22.04, that’s a plan you need.

It’s peer, not ident

This one isn’t about time. From the opening of the write-up’s section 2:

When postgres is installed, postgres is set up to use ident authentication. Configured this way, postgres ties into operating system accounts.

The behavior it’s describing is right — you’re authenticated by your OS account name. But that behavior isn’t called ident. The PostgreSQL docs separate the two:

Same goal, different mechanism and different scope. peer asks the kernel who’s on the other end of the Unix socket; ident asks an ident server on the client, over the network. Which is why ident is TCP-only.

The docs add one more sentence:

When specified for local connections, peer authentication will be used instead.

Write ident on a local line and peer is what actually runs. That’s why the write-up’s account doesn’t end up describing wrong behavior. The name is still wrong.

Ubuntu’s own documentation states it outright:

In Ubuntu, peer is the default authentication method used for local connections, while scram-sha-256 is the default for host connections.

Knowing the right name matters because it changes what word you’re looking for when you open pg_hba.conf. The line to edit says local ... peer, and you’ll stall there hunting for ident. Worse, switching it to ident when adding remote access asks for something else entirely — an ident server on the client.

Creating a role doesn’t create an Ubuntu account

The same paragraph continues:

That is, if you create a new role A in postgres and grant A permissions (a) and (b), a user named A is created on ubuntu, and if we log into ubuntu as user A and connect to postgres, we can use permissions (a) and (b).

The direction is reversed. The definition of peer is the answer:

…and check if it matches the requested database user name.

It checks; it doesn’t create. PostgreSQL never creates operating system accounts. So the order you actually need is: create the Ubuntu account, create a PostgreSQL role with the same name, then log in as that account and connect. Two separate things, and the names have to match.

This misunderstanding leads somewhere concrete. Run CREATE ROLE myapp alone and then sudo -u myapp psql, and Ubuntu doesn’t know any myapp.

The install log line the write-up cites as evidence is worth a second look too.

Adding user postgres to group ssl-cert

That’s a line about putting the postgres user into a group, not about creating one. The postgres OS account does get created during package installation — but not by this line. The /etc/passwd check the write-up offers right afterwards is the check that actually shows it.

cut -f1 -d: /etc/passwd | grep postgres

You no longer need to spell out postgresql-contrib

The write-up’s install commands:

sudo apt update
sudo apt install postgresql postgresql-contrib

Ubuntu Server’s current documented instruction is one line:

sudo apt install postgresql

The postgresql-contrib package hasn’t disappeared. It’s still in 24.04, a version-tracking metapackage described as “additional facilities for PostgreSQL (supported version).” But its dependency points at postgresql-contrib-16, a virtual package that postgresql-16 provides — so installing postgresql alone brings the contrib modules along. Spelling it out costs nothing; it just isn’t a line you need any more.

The modules the write-up names to explain contrib — pg_stat_statements, pgrowlocks, pgcrypto — are all still in there.

If you want to pick the version

The structure of that table is the constraint. Use distribution packages and the Ubuntu release picks your version. PostgreSQL’s download page says so plainly:

Ubuntu “snapshots” a specific version of PostgreSQL that is then supported throughout the lifetime of that Ubuntu version. If the version included in your version of Ubuntu is not the one you want, you can use the PostgreSQL Apt Repository.

So if you want something other than 14 on 22.04, or want to keep PostgreSQL current without moving releases, you attach the PGDG repository.

sudo apt install -y postgresql-common
sudo /usr/share/postgresql-common/pgdg/apt.postgresql.org.sh

Supported targets are 26.10, 26.04 LTS, 24.04 LTS, and 22.04 LTS. 20.04 isn’t on the list.

What still holds

Versions and terminology changed; the way the procedure is explained still works.

Showing why psql fails before explaining it. The write-up just runs psql, gets role "sehyeona" does not exist, and then explains. Leading with the error that peer demands your OS account name as the role name sticks better than laying out the concept first.

Two ways to connect, side by side. Switching accounts first versus doing it in one line:

# switch the shell to postgres, then connect
sudo -i -u postgres
psql

# connect directly without going through a shell
sudo -u postgres psql

Clusters and pg_ctlcluster. Explaining it as cluster > database > table, and noting that Debian-family packaging has pg_ctlcluster for running several versions and clusters, both hold. Given how the table above splits versions, that’s knowledge you need more now, not less.

Reading process structure with ps -ef | grep postgres and pstree. One parent process with logger, checkpointer, autovacuum and other background processes hanging off it is a picture that doesn’t depend on version.

Wrapping up

• The PostgreSQL 12 this guide gets you went end-of-life on November 21, 2024. Ubuntu 20.04’s standard support ended in May 2025.
• 14, the default on Ubuntu 22.04, ends November 12, 2026. Two months out.
• It’s peer, not ident. ident is TCP-only and asks an ident server on the client. Write ident on a local line and peer runs anyway.
• Creating a role doesn’t create an Ubuntu account. peer only checks that the names match. Create both, separately, with the same name.
• You no longer need postgresql-contrib spelled out. Ubuntu’s documented instruction is sudo apt install postgresql.
• Distribution packages mean the release pins the version. For a different one, attach the PGDG repository.
• Showing the error before the explanation, clusters, pg_ctlcluster, and the process-structure walkthrough all still hold.

What ages in an install guide is usually the version numbers, and one table refreshes those. What lasted was the part where a name was wrong. ident and peer were different things four years ago and they’re different now. Time doesn’t fix that kind, so learn it wrong once and it catches you every time you open pg_hba.conf.

Since installing and using it was the point, here’s the order again. The release picks the version, so check that first (and reach for PGDG if you need to), installation is one postgresql line, and the next place you stall is connecting. Knowing that the word in that slot is peer gets you both the line to edit in pg_hba.conf and the fact that you need a matching OS account, in one go.

References

• Versioning Policy — PostgreSQL
• The pg_hba.conf File — PostgreSQL
• Install and configure PostgreSQL — Ubuntu Server documentation
• Linux downloads (Ubuntu) — PostgreSQL
• Ubuntu release cycle
• Source: [PostgreSQL] Installing PostgreSQL on ubuntu