How to fix ERROR 1034: Incorrect key file; try to repair in MySQL

# On Linux/Unix:
tail -100 /var/log/mysql/error.log

# On Windows:
type "C:\ProgramData\MySQL\MySQL Server 8.0\error.log"

# Or query the current log file location:
SHOW VARIABLES LIKE 'log_error';

# Check overall filesystem usage:
df -h

# Check specific MySQL data directory:
du -sh /var/lib/mysql

# Check space on that partition:
df -h /var/lib/mysql

# Check tmpdir space:
df -h /tmp

# Or see configured tmpdir in MySQL:
SHOW VARIABLES LIKE 'tmpdir';

# Check mount status:
mount | grep -E "mysql|var|data"

# Look for "ro" in the output. If present, remount as read-write:
sudo mount -o remount,rw /var/lib/mysql

# Verify the remount succeeded:
mount | grep /var/lib/mysql

# Test write access:
sudo touch /var/lib/mysql/.write_test && sudo rm /var/lib/mysql/.write_test

# Check directory permissions:
ls -ld /var/lib/mysql
ls -l /var/lib/mysql/database_name/

# The mysql user should own these directories:
sudo chown -R mysql:mysql /var/lib/mysql
sudo chmod 750 /var/lib/mysql

# Verify:
ls -ld /var/lib/mysql

# First, flush and lock the table:
FLUSH TABLES table_name FOR EXPORT;

# Repair the table:
REPAIR TABLE table_name;

# Or for quick repair (safer):
REPAIR TABLE table_name QUICK;

# Or for extended repair (slower, more thorough):
REPAIR TABLE table_name EXTENDED;

# Check table status:
CHECK TABLE table_name;

# Stop MySQL:
sudo systemctl stop mysql

# Try quick repair first (fastest):
myisamchk -r -q /var/lib/mysql/database_name/table_name.MYI

# If quick repair fails, try standard repair:
myisamchk -r /var/lib/mysql/database_name/table_name.MYI

# If that fails, try safe recovery (slowest):
myisamchk --safe-recover /var/lib/mysql/database_name/table_name.MYI

# Start MySQL:
sudo systemctl start mysql

# Verify the table:
CHECK TABLE table_name;

# Rebuild the table (may take time for large tables):
ALTER TABLE table_name FORCE;

# Or:
ALTER TABLE table_name ENGINE=InnoDB;

# Verify:
CHECK TABLE table_name;

# Check if a backup exists:
ls -lh /path/to/backups/

# If using mysqldump backup:
mysqldump -u root -p database_name < /path/to/backup.sql

# Or if using Percona XtraBackup:
xtrabackup --prepare --target-dir=/mnt/backup
xtrabackup --copy-back --target-dir=/mnt/backup

# Restart MySQL:
sudo systemctl restart mysql

# Verify it started:
sudo systemctl status mysql

# Test with a simple query:
mysql -u root -p -e "SELECT COUNT(*) FROM table_name;"

# Monitor error log:
tail -f /var/log/mysql/error.log

# Set up monitoring for disk space and table status