How to fix Config file error in PostgreSQL

The most important first step is to examine the PostgreSQL logs to find the specific error. Look for messages that occur before the "contains errors" message, as they will identify the exact problem.

On Linux systems, check the log file location:

# Default location
cat /var/lib/postgresql/data/pg_log/postgresql.log

# Or use journalctl if using systemd
journalctl -u postgresql -n 50

The log will show messages like:

LOG: syntax error in file "/var/lib/postgresql/data/postgresql.conf" line 237, near token "\""
FATAL: configuration file "/var/lib/postgresql/data/postgresql.conf" contains errors

This tells you the exact file, line number, and the problematic token.

Once you know which line has the error, open the configuration file and examine that line and surrounding context.

# View the problematic section
sed -n "230,240p" /var/lib/postgresql/data/postgresql.conf

Common syntax errors to look for:
- Using double quotes (") instead of single quotes ('): log_line_prefix = "some value" should be log_line_prefix = 'some value'
- Missing or extra spaces around the equals sign
- Incomplete or unterminated strings
- Invalid numeric values or units (e.g., "5000 MB" instead of "5000MB")

Correct the identified syntax errors:

# Example: Fix quote style
# Wrong:
log_line_prefix = "user=%u,db=%d,app=%a [%p]"

# Correct:
log_line_prefix = 'user=%u,db=%d,app=%a [%p]'

# Example: Fix value format
# Wrong:
shared_buffers = 4 GB

# Correct:
shared_buffers = 4GB

# Example: Single quotes with embedded single quote
# Correct (use two single quotes):
log_line_prefix = 'user=''%u''

Remember:
- One parameter per line
- Use single quotes for values that are not simple identifiers or numbers
- Embed single quotes using two consecutive quotes (preferred) or backslash-quote
- Comments begin with # and extend to end of line

Before restarting PostgreSQL, validate the configuration to catch any remaining errors:

# Check configuration without starting the server
postgres -C config_file

# Or use pg_ctl to check the configuration
su - postgres
pg_ctl -D /var/lib/postgresql/data -c

For a more detailed check, you can also query the pg_file_settings view (requires a running PostgreSQL instance):

SELECT name, sourcefile, sourceline, setting, error 
FROM pg_catalog.pg_file_settings 
WHERE error IS NOT NULL;

This view shows all configuration file settings and any errors detected during parsing, allowing you to fix issues before attempting a reload.

After fixing the syntax errors, reload the configuration:

# Reload configuration without restarting (for PGC_SIGHUP parameters only)
su - postgres
pg_ctl reload -D /var/lib/postgresql/data

# Or reload via SQL if the server is running
psql -U postgres -c "SELECT pg_reload_conf();"

# If you need to restart (for PGC_POSTMASTER parameters like shared_buffers)
sudo systemctl restart postgresql

# Or using pg_ctl
su - postgres
pg_ctl restart -D /var/lib/postgresql/data

After reloading or restarting, check the logs again to confirm there are no new errors.