How to fix Crash shutdown in PostgreSQL

Examine the PostgreSQL server logs to identify what caused the crash. Look for segmentation faults, out-of-memory messages, or disk errors.

# On Linux, typically:
tail -f /var/log/postgresql/postgresql.log

# Or in the data directory:
tail -f /var/lib/postgresql/[VERSION]/main/log/postgresql.log

Look for messages like:
- "Segmentation fault"
- "Out of memory"
- "Connection lost unexpectedly"
- "Invalid page header"

Insufficient disk space is a common cause. Verify there is enough space for recovery and WAL replay.

df -h
# Check the partition where PostgreSQL data directory is located

# Check the size of the WAL files:
du -sh /var/lib/postgresql/[VERSION]/main/pg_wal/

Ensure at least 20-30% of disk space is free before restarting.

By default, PostgreSQL is configured with restart_after_crash = on, which means it will automatically restart and perform crash recovery.

# Start/restart PostgreSQL (it will auto-recover):
sudo systemctl restart postgresql

# Or using pg_ctl:
sudo -u postgres pg_ctl restart -D /var/lib/postgresql/[VERSION]/main

Watch the logs as it replays the WAL:

tail -f /var/log/postgresql/postgresql.log | grep -i recovery

Wait for the message: "database system is ready to accept connections"

Once recovery completes and the server is running, verify the integrity of critical tables.

sudo -u postgres psql

-- Check for corruption:
REINDEX DATABASE postgres;

-- Run integrity checks on specific tables:
CHECK TABLE your_table_name;

-- Monitor recovery progress:
SELECT pg_is_in_recovery();

If any tables show corruption, restore from your backup.

Once the server is stable, identify the root cause to prevent future crashes.

For OOM crashes:

# Check memory usage and set appropriate limits:
free -h

# Adjust PostgreSQL shared_buffers if necessary (in postgresql.conf):
shared_buffers = 256MB  # For 4GB RAM server

# Restart PostgreSQL for changes to take effect:
sudo systemctl restart postgresql

For segmentation faults:
- Check PostgreSQL version: SELECT version();
- Update to the latest stable version if you're on an old version
- Report the crash dump to PostgreSQL developers if it's reproducible

For disk I/O failures:
- Run disk diagnostics: sudo smartctl -a /dev/sda
- Check filesystem integrity: sudo fsck /mount/point (unmount first)
- Replace faulty hardware if needed

By default, PostgreSQL is configured well for crash recovery. However, you can verify these settings:

sudo -u postgres psql

-- View recovery settings:
SHOW restart_after_crash;
SHOW wal_level;
SHOW max_wal_senders;  -- For replication

Recommended settings in postgresql.conf:

# Ensure automatic recovery is enabled
restart_after_crash = on

# Use WAL archiving for faster recovery
wal_level = replica
archive_mode = on
archive_command = 'test ! -f /archive/%f && cp %p /archive/%f'

Reload the configuration:

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