Find and inspect the blocks reserved for root that keep a filesystem usable when it is nearly full. 18.12.2025 | reading time: 2 min A filesystem reserves a slice of its blocks for the system and root to prevent complete fill-up and to help recovery; this short guide shows how to inspect those blocks so he can decide whether to adjust or leave them alone. Quick hands-on example Create a tiny ext4 image, build the filesystem with the default 5 percent reservation and read the superblock: ```truncate -s 10M test.img; mkfs.ext4 -F -m 5 test.img; tune2fs -l test.img | egrep "Block count|Block size|Reserved block count"``` ```OUTPUT: Block count: 2560; Block size: 4096; Reserved block count: 128``` Compute reserved bytes from filesystem stats Inspect the filesystem view and derive reserved blocks with `stat -f`, then compute bytes by multiplying the difference `f_bfree - f_bavail` with the fragment size; for the example image `stat -f test.img` might show free 2432 and available 2304 so reserved blocks = 128 and reserved bytes = 128 * 4096 = 524288. Adjusting and caveats To change the reservation percentage use `tune2fs -m PERCENT /dev/DEVICE` but be cautious: reducing the reserve to zero on an OS volume can prevent emergency recovery, some filesystems (for example XFS) do not use the ext-style reservation, and large modern storage often benefits from lowering the default 5 percent on big data partitions. Commands that reveal the details Use `tune2fs -l` or `dumpe2fs -h` to read superblock values, `stat -f` to compare free versus available blocks, and `df` to see the space presented to unprivileged users; together they show who can use the hidden space and why. Final thought Knowing how to find and calculate reserved blocks helps him avoid false alarms and make informed decisions when tuning storage; consider deepening his knowledge with CompTIA Linux+ or LPIC-1 and intensive exam preparation at bitsandbytes.academy. Join Bits & Bytes Academy First class LINUX exam preparation. filesystem utilities storage troubleshooting
