How to Quickly Identify Disk Space Hogs on Linux Servers

During routine server operations you may receive a disk‑space warning. First, verify the reported usage with df -Hl and compare it to the alert.

Finding Large Directories with du

A simple method is to run du -hs * in the root directory to list each subdirectory’s size, then drill down recursively.

For a more efficient search, limit the depth and filter the results:

du -h -d 2 | grep [GT] | sort -nr
# or
du -h --max-depth=2 | grep [GT] | sort -nr

This lists directories whose sizes are expressed in gigabytes (G) or terabytes (T) and sorts them descending.

Using find for Large Files

The find command can locate large files quickly: find / -type f -size +1G -exec du -h {} \; Compared to du, find is often faster and more flexible.

Detecting Deleted Files Still Holding Space

If the summed sizes from du are far less than the total used space shown by df, deleted files may still be open. Use lsof +L1 to list such files: lsof +L1 The output may reveal large log files (e.g., a 28 GB file) that were deleted but not released. Restarting the associated service (e.g., Tomcat) frees the space.

Understanding Reserved Space

Linux filesystems reserve a percentage (default 5%) of disk space for the root user, which can cause the Used + Avail values to be less than Size. Adjust the reservation with tune2fs: tune2fs -m 1 /dev/vda1 Reducing the reserved percentage from 5% to 1% releases the hidden space, as shown by the before‑and‑after comparison.

By following these commands, you can efficiently pinpoint the root cause of disk‑space exhaustion and resolve it.