# df (disk free)

> How to read df output, why Use% can reach 100% before Avail is zero for normal users, and how to check inodes with df -i.

df (disk free) is the standard command that shows the size, used space, available space and mount point of each mounted file system. 'df -h' prints sizes in human-readable units; 'df -i' shows inode usage instead of bytes, which explains 'No space left on device' errors when bytes are still free.

## Reading the columns

Filesystem is the device, Size the total, Used and Avail the space used and free for normal users, Use% the percentage, and Mounted on the directory where it appears.

On ext4, about 5% is reserved for root by default, so Used + Avail can be smaller than Size and normal users can run out before Use% shows 100%.

## Useful options

'-T' adds the file system type, '-x tmpfs' hides temporary memory file systems, and 'df -h /var' shows only the file system that holds /var.

## How to check free space

1. Run: df -hT -x tmpfs
2. Find the file system with high Use%.
3. Check inodes too: df -i
4. Then look inside with du or ncdu to find what uses the space.

## Cautions

- Never fill the root file system to 100%: services, logins and package updates can fail.

## Sources

- [df(1)](https://man7.org/linux/man-pages/man1/df.1.html)
- [inode(7)](https://man7.org/linux/man-pages/man7/inode.7.html)

Last updated: 2026-10-08
URL: https://raincleaner.eu/wiki/linux/df-disk-free