How to fix ERROR 1026: Error writing file in MySQL

Run the disk usage command to identify space issues:

df -h

Look for the mount point containing your MySQL data directory (typically /var/lib/mysql or /data). If "Use%" shows 100% or very close (95%+), disk space is the problem. You must free up disk space or expand the volume before continuing.

To free space:
- Delete old binary logs: mysql -u root -p -e "PURGE BINARY LOGS BEFORE DATE_SUB(NOW(), INTERVAL 7 DAY);"
- Remove old temporary files: rm -f /tmp/mysql*
- Check for large tables that can be archived or truncated

Check that the mysql system user owns the data directory:

ls -la /var/lib/mysql | head -5

The output should show "mysql mysql" as owner/group. If not, fix permissions:

sudo chown -R mysql:mysql /var/lib/mysql
sudo chmod -R 750 /var/lib/mysql

On Windows or custom paths, ensure the MySQL service account (usually "MySQL80" or similar) has full control over the data directory through file properties.

List mounted filesystems to identify read-only mounts:

mount | grep -E "ro|rw"

If the MySQL data directory is mounted with "ro" (read-only), remount it as read-write:

sudo mount -o remount,rw /var/lib/mysql

Or remount the entire filesystem:

sudo mount -o remount,rw /

A read-only filesystem often indicates a hardware issue, kernel panic, or filesystem corruption. Check system logs after remounting:

sudo dmesg | tail -20

Find your MySQL temp directory:

mysql -u root -p -e "SHOW VARIABLES LIKE 'tmpdir';"

Check that the tmpdir path exists and is writable by the mysql user:

sudo ls -la /tmp/mysql
sudo chmod 1777 /tmp

If using a custom tmpdir, ensure it has sufficient free space and proper ownership. For containerized MySQL, verify your Docker volume or container tmpfs has adequate space.

Check the MySQL error log for detailed error information:

sudo tail -100 /var/log/mysql/error.log | grep -A 2 "1026"

The error message format is: "ERROR 1026: Error writing file 'filename' (errno: XX - description)"

Common errno values:
- errno 28: No space left on device (disk full)
- errno 13: Permission denied
- errno 2: No such file or directory
- errno 30: Read-only file system

Address the specific errno according to the cause identified above.

After fixing filesystem issues, restart the MySQL service:

sudo systemctl restart mysql

Or on older systems:

sudo /etc/init.d/mysql restart

Monitor the error log during startup:

sudo tail -f /var/log/mysql/error.log

If replication is enabled, wait for the replica to catch up to the master before resuming application traffic:

mysql -u root -p -e "SHOW SLAVE STATUS\G" | grep "Seconds_Behind_Master"