---
title: df — check available disk space
date: 2026-10-18
time: 12:00
model: admin
category: programs
author_type: human
summary: Command that checks total, used, and available capacity and usage percentage for each mounted filesystem. Includes practical inspection procedures and examples.
tags: program, File and disk management, df
---

**💬 "df Command"**

While du shows usage **by folder**, df shows total, used, and available capacity **by mounted filesystem (partition)**. It is one of the first commands run during server health checks.

Because the default output uses 1K blocks and is hard to read, always add `-h` in practice.

- **Concept**: Check disk usage by filesystem. See at a glance which mount point is at risk.
- **Left column**: `Filesystem` — The name of the mounted device (e.g. /dev/vda1) or virtual filesystem (tmpfs).
- **Right column**: `Mounted on` — The path where the device is attached. This is where issues actually occur.
- **Size / Used / Avail**: Total / used / remaining capacity. If Avail is close to 0, writes will fail soon.
- **Use%**: Usage percentage. If it exceeds 90%, review log rotation and cleanup.
## Commonly Used Options

| Option | Description |
| --- | --- |
| -h | Output in human-readable units (K/M/G) |
| -T | Also display the filesystem type (ext4, xfs, tmpfs, etc.) |
| -i | Show inode usage instead of capacity (diagnose file count exhaustion) |
| -x tmpfs | Exclude virtual filesystems such as tmpfs |
| --total | Add a total summary line at the bottom |

## 3 Essential Command Combinations

- `df -h` — Check per-mount capacity in readable units (most basic)
- `df -hT -x tmpfs -x devtmpfs` — View only real disks together with their filesystem type
- `df -ih /var` — Check inode exhaustion when capacity remains but files cannot be created
**💬 "Give an example of the process of narrowing down the cause"**

Common situations on production servers are organized below in the order they typically occur.

### Step 1 · Identify Which Mount Has a Problem

Look at all mounts and find the point with high usage.

```
df -hT -x tmpfs
```

### Step 2 · Find the Culprit Inside It

Move to the problem mount and sort usage by folder in descending order.

```
cd /var && du -sh * | sort -h | tail -5
```

### Step 3 · Verify After Cleanup

Clear logs or delete old backups, then check again. If the numbers remain the same after deletion, a process is still holding the file.

```
df -h /var && lsof +L1 | head
```

## How It Is Used in Practice

### 1. Capacity Check Before Deployment

**Situation** — Before deploying a new release, you need to check that the target partition has enough free space.

```
df -h /var /data && df -hT -x tmpfs
```

**Result** — Check whether Avail is sufficiently larger than the release size (e.g. 2G). If usage is 90% or more, stop the deployment and clean up first.

**Point** — Putting a df check at the beginning of the deployment script can prevent disk shortage incidents.

### 2. Capacity Remains but File Creation Fails

**Situation** — Free space is 40%, but new log files cannot be created and "No space left on device" appears.

```
df -ih /var
```

**Result** — If IUse% is 100%, inodes are exhausted. You need to clean up directories that contain many small files.

**Point** — This is a typical failure missed if you only check capacity (%). Include df -ih in your checks.

## Things to Watch Out For

- Even if Avail is 0, 5% reserved blocks remain for root, allowing only the administrator to use it briefly.
- When Use% exceeds 90%, system behavior starts to become unstable. Set up threshold alerts.
- For network filesystems such as NFS, df may appear to hang because responses are slow.
- tmpfs and overlay use memory/images, so they differ from actual disk capacity. Exclude them with -x.
## Actual Execution Output

This is the result of checking per-mount capacity and usage in readable units.

![df command execution result: capacity and usage by filesystem](https://games.aidebatehub.com/assets/df-demo.png)

A production server

---
Source (HTML): https://games.aidebatehub.com/programs/linux/filesystem/df.html
This file is an auto-generated Markdown twin of the DevHub document.