How to Find What Is Filling Up Disk Space on a Linux Server

Disk full alerts at 2am? Learn the exact commands to find what's eating your Linux server's disk space and fix it fast. You get the alert: disk usage at 94%. Your app starts throwing errors, logs stop writing, and databases refuse to accept new rows. Finding the culprit fast matters — but on a server with millions of files, knowing where to look is half the battle. Here's a systematic approach to track down disk hogs in minutes, not hours. Start With the Big Picture: df Before you dig into directories, confirm which filesystem is actually full. Run: df -h — shows all mounted filesystems with human-readable sizes df -h / — focus on the root filesystem df -i — check inode usage (a filesystem can be 'full' even with free space if inodes are exhausted) Pay attention to the 'Use%' column. If you see 100% on /var or /home but not /, that tells you exactly which mount point to investigate. Inode exhaustion — df -i showing 100% — is easy to miss and causes the same symptoms as a full disk, so always check both. Drill Down With du Once you know which mount point is full, use du to find the largest directories. Start from the top of that mount point and work down: du -sh /* 2>/dev/null — sizes of every top-level directory, errors suppressed du -sh /var/* 2>/dev/null — drill into /var if that's the culprit du -ah /var | sort -rh | head -20 — list the 20 largest files and folders inside /var The pattern is always the same: run du -sh on the suspicious directory, find the largest subdirectory, repeat one level deeper. You'll usually hit the real culprit within three or four iterations. Common offenders are /var/log (runaway logs), /var/lib/docker (unused images and volumes), and /tmp (applications that don't clean up after themselves). Find Large Files Directly With find Sometimes a single enormous file is the problem — a core dump, a forgotten database export, or a log that rotated incorrectly. Use find to surface files above a size threshold: find / -xdev -size +500M -ls 2>/de