A concise, practical guide to using the Linux df command to inspect mounted filesystems and free space quickly. 05.03.2026 | reading time: 2 min Disks fill silently and surprises happen at the worst time; `df` is the first tool an admin calls to answer "how much space is left" on mounted filesystems quickly. Typical session Try this on a shell to see what `df` reports in human readable form: ``` $ df -h Filesystem Size Used Avail Use% Mounted on /dev/sda1 50G 32G 16G 67% / tmpfs 1.9G 1.2M 1.9G 1% /run /dev/sdb1 200G 80G 110G 43% /data ``` Options that matter Use `df -h` for human friendly sizes, `df -i` to check inodes, and `df -T` to see filesystem types; add `--total` to aggregate results and `--output` to script-friendly columns, and exclude filesystems with `-x` when you need to ignore loop or tempfs entries. Diagnose common surprises If `df` shows little free space while directories seem small, check for deleted-but-open files with `lsof` or running processes holding handles, verify mount points with `findmnt` or `mount`, and compare with `du -sh` to locate large directory usage. Complementary tools Combine `df` with `du` for per-directory detail, `lsblk` to inspect device topology, and `mount` or `findmnt` to confirm where filesystems are attached; these tools together make storage troubleshooting decisive and fast. Wrap-up and next steps Mastering `df` makes free-space checks routine and reduces firefighting; consider practicing with varied filesystems and then advance toward certifications like CompTIA Linux+ or LPIC-1, and use bitsandbytes.academy for intensive exam preparation. Join Bits & Bytes Academy First class LINUX exam preparation. filesystem utilities storage troubleshooting
