How to fix FATAL: could not open file 'pg_version': No such file or directory in PostgreSQL

First, confirm that you're pointing to the correct PostgreSQL data directory. Common paths are /var/lib/postgresql/data (Linux), /Library/PostgreSQL/data (macOS), or C:\Program Files\PostgreSQL\data (Windows).

Check your postgresql.conf file or environment variables:

grep -i 'data_directory' /etc/postgresql/*/main/postgresql.conf
# or
echo $PGDATA

The data directory should contain files like PG_VERSION, pg_control, base/, and global/.

List the contents of your data directory to confirm whether pg_version is missing:

ls -la /var/lib/postgresql/data/ | grep -i pg_version

You should see a file named PG_VERSION (note the case on Linux/macOS). If it's missing, proceed to the next steps. If it exists but PostgreSQL still reports it's missing, check file permissions:

ls -la /var/lib/postgresql/data/PG_VERSION

The file should be readable by the postgres user.

Before making any changes, stop the PostgreSQL server and create a backup:

# Stop PostgreSQL
sudo systemctl stop postgresql
# or
sudo service postgresql stop

# Backup the entire data directory
sudo cp -r /var/lib/postgresql/data /var/lib/postgresql/data.backup

This backup is critical - if recovery fails, you'll have the option to restore.

You have two options:

Option A: Restore from a fresh initialization

If you have another PostgreSQL cluster of the same version, copy the PG_VERSION file:

cd /var/lib/postgresql/data
sudo cat /path/to/working/data/PG_VERSION

Note the version number (e.g., '13' for PostgreSQL 13). Then create it in your damaged directory:

sudo bash -c 'echo 13 > /var/lib/postgresql/data/PG_VERSION'
sudo chown postgres:postgres /var/lib/postgresql/data/PG_VERSION
sudo chmod 600 /var/lib/postgresql/data/PG_VERSION

Option B: Re-initialize the cluster (data loss)

If you don't have a backup, you must reinitialize the data directory:

# Remove the corrupted directory
sudo rm -rf /var/lib/postgresql/data

# Reinitialize as postgres user
sudo -u postgres /usr/lib/postgresql/13/bin/initdb -D /var/lib/postgresql/data

This will create a new empty cluster. You'll lose all data unless you have a separate pg_dumpall backup.

After restoring PG_VERSION, ensure correct ownership and permissions:

sudo chown -R postgres:postgres /var/lib/postgresql/data
sudo chmod 700 /var/lib/postgresql/data
sudo chmod 600 /var/lib/postgresql/data/PG_VERSION

On Linux, verify with:

ls -la /var/lib/postgresql/data/ | head -20

The postgres user must be the owner and the data directory must have mode 700 (rwx------).

Attempt to start PostgreSQL:

sudo systemctl start postgresql
# or
sudo service postgresql start

Check the status and logs:

sudo systemctl status postgresql
sudo tail -f /var/log/postgresql/postgresql.log

If PostgreSQL starts successfully, verify connectivity:

sudo -u postgres psql -c "SELECT version();"

This command should display the PostgreSQL version information.