How to Quickly Identify Disk Space Hogs on Linux Servers

Understanding Disk Space Alerts

During routine server operations, administrators often receive alerts indicating that disk space is running low. The first step is to verify the reported usage with df -Hl, which shows the overall filesystem statistics.

Finding Large Directories with du

A straightforward method is to run du -hs * in the root directory, which lists each top‑level directory and its size. Repeating the command in subdirectories narrows down the culprit.

For a more efficient search, use the depth option of du (e.g., du -h --max-depth=2) and pipe the output to grep to filter entries that show sizes in G or T.

Using find to Locate Large Files

The find command can directly list files larger than a given size, which is often faster and more flexible than du: find / -type f -size +1G -exec du -h {} \; This command searches the entire filesystem for regular files exceeding 1 GB and displays their sizes.

Detecting Deleted Files Still Holding Space

Sometimes the space reported by df does not match the sum of sizes shown by du. This discrepancy usually means that deleted files are still open by a process, preventing the space from being reclaimed.

Use lsof +L1 to list such files: lsof +L1 The output often reveals large log files that have been removed but are still held by a running service (e.g., a 28 GB log file). Restarting the associated service (such as Tomcat) releases the space.

Adjusting Reserved Space with tune2fs

Linux filesystems reserve a percentage of disk space for the root user (default 5%). This reservation can make it appear that some space is “missing.” To change the reserved percentage, run: tune2fs -m 1 /dev/vda1 After adjusting the reservation, the previously hidden space becomes available, as shown in the before‑and‑after screenshots.

Conclusion

By combining df, du, find, and lsof, administrators can quickly locate the directories or files that consume excessive disk space, identify hidden usage caused by deleted but still‑open files, and adjust filesystem reservations with tune2fs to reclaim space.