Among the plethora of commands available, df stands out as a crucial command for managing and understanding disk space on your Linux system. In this comprehensive guide, we will delve into the nuances of the df command, exploring its syntax, various options, and real-world applications.
Whether you are a seasoned system administrator, a budding developer, or simply a curious Linux enthusiast, understanding how to effectively use the df command can greatly enhance your ability to monitor and manage your system’s resources. So, let’s embark on this journey to uncover the capabilities of the df command, armed with examples, FAQs, and personal insights that will demystify this powerful Linux tool.
What is the df command?
The df command in Linux stands for “disk free.” It’s a simple yet powerful command used to display the amount of available and used disk space on all mounted filesystems. Whether you’re a system admin, a developer, or just a Linux enthusiast, knowing how to use df is essential.
Basic syntax of df
The basic syntax of the df command is quite straightforward:
df [options] [file...]
Here, [options] are the flags you can use to modify the output, and [file...] refers to a specific file or directory you want to check the disk space for.
Understanding df output
When you run df, the output typically shows several columns:
- Filesystem: The name of the filesystem.
- 1K-blocks (or Size): Total size of the filesystem.
- Used: Amount of space used.
- Available: Amount of space available.
- Use%: Percentage of the filesystem that is used.
- Mounted on: Directory on which the filesystem is mounted.
Let’s run a basic df command and see what the output looks like:
$ df
You might see something like this:
Filesystem 1K-blocks Used Available Use% Mounted on
udev 2048060 0 2048060 0% /dev
tmpfs 413500 1340 412160 1% /run
/dev/sda1 102535924 9053964 88226340 10% /
tmpfs 2067480 24684 2042796 2% /dev/shm
tmpfs 5120 4 5116 1% /run/lock
tmpfs 2067480 0 2067480 0% /sys/fs/cgroup
/dev/sda6 366284644 8761234 339151072 3% /home
tmpfs 413496 52 413444 1% /run/user/1000
Examples
Let’s walk through some practical examples of how df can be used:
1. Checking disk space in human-readable format
Personally, I find the default output a bit hard to digest due to its use of 1K-blocks. To make it more readable, use the -h option:
$ df -h Filesystem Size Used Avail Use% Mounted on udev 2.0G 0 2.0G 0% /dev tmpfs 404M 1.4M 403M 1% /run /dev/sda1 98G 8.6G 84G 10% / tmpfs 2.0G 24M 1.9G 2% /dev/shm /dev/sda6 350G 8.4G 323G 3% /home
This command will display the disk space in MB, GB, etc., which is much easier to understand.
2. Displaying the filesystem type
Sometimes, I need to know the type of filesystem I’m dealing with. The -T option comes in handy:
$ df -T Filesystem Type 1K-blocks Used Available Use% Mounted on udev devtmpfs 2048060 0 2048060 0% /dev /dev/sda1 ext4 102535924 9053964 88226340 10% / /dev/sda6 ext4 366284644 8761234 339151072 3% /home
3. Including and excluding certain filesystem types
If I want to include or exclude specific filesystem types, I use the -t and -x options, respectively. For example, to only show ext4 filesystems:
$ df -t ext4 Filesystem 1K-blocks Used Available Use% Mounted on /dev/sda1 102535924 9053964 88226340 10% / /dev/sda6 366284644 8761234 339151072 3% /home
And to exclude tmpfs filesystems:
$ df -x tmpfs Filesystem 1K-blocks Used Available Use% Mounted on udev 2048060 0 2048060 0% /dev /dev/sda1 102535924 9053964 88226340 10% / /dev/sda6 366284644 8761234 339151072 3% /home
4. Checking disk space for a specific directory
At times, I only need to check the disk space related to a specific directory. This can be done by:
$ df /path/to/directory
$ df /home Filesystem 1K-blocks Used Available Use% Mounted on /dev/sda6 366284644 8761234 339151072 3% /home
5. Including all filesystems (-a)
This option includes dummy filesystems and those with 0-block sizes that are usually omitted from the standard df output.
$ df -a Filesystem 1K-blocks Used Available Use% Mounted on sysfs 0 0 0 - /sys proc 0 0 0 - /proc udev 2048060 0 2048060 0% /dev /dev/sda1 102535924 9053964 88226340 10% / ...
6. Showing inode information (-i)
Instead of showing block usage, this displays the inode information, which is useful when you’re dealing with a large number of small files.
$ df -i Filesystem Inodes IUsed IFree IUse% Mounted on udev 511515 402 511113 1% /dev /dev/sda1 6553600 480234 6073366 8% / /dev/sda6 24419000 345678 24063322 2% /home
7. Displaying the disk usage in 1024-byte blocks (-k)
This is the default setting, but can be explicitly set using -k. It displays disk space in 1024-byte (1K) blocks.
$ df -k Filesystem 1K-blocks Used Available Use% Mounted on /dev/sda1 102535924 9053964 88226340 10% / /dev/sda6 366284644 8761234 339151072 3% /home
8. Limiting the output to local filesystems (-l)
This is useful when you want to ignore remote filesystems and focus only on the local ones.
$ df -l Filesystem 1K-blocks Used Available Use% Mounted on /dev/sda1 102535924 9053964 88226340 10% / /dev/sda6 366284644 8761234 339151072 3% /home
9. Producing a grand total (--total)
This option is particularly useful when you want a summary of the total disk space used and available across all filesystems. It appends a grand total at the end of the output.
$ df --total Filesystem 1K-blocks Used Available Use% Mounted on udev 2048060 0 2048060 0% /dev /dev/sda1 102535924 9053964 88226340 10% / /dev/sda6 366284644 8761234 339151072 3% /home ... total 470916628 17815632 442534372 4%
10. Ensuring data is up to date (--sync)
By using the --sync option, df performs a sync before getting the usage data. This ensures that the information provided is up to date, reflecting any recent changes to the filesystem.
$ df --sync Filesystem 1K-blocks Used Available Use% Mounted on /dev/sda1 102535924 9053964 88226340 10% / /dev/sda6 366284644 8761234 339151072 3% /home ...
The output looks similar to the standard df output, but with the assurance that all recent changes to the disk are accounted for.
Useful df command options
To further enhance your understanding and usage of the df command, here’s a table summarizing some of the most useful options. This table is a handy reference that I often turn to when using df in various scenarios.
| Option | Description |
|---|---|
-h |
Displays the disk space in a human-readable format (e.g., KB, MB, GB). |
-a |
Includes all filesystems, including those with 0 blocks, which are usually omitted. |
-T |
Shows the type of each filesystem. |
-t [type] |
Displays filesystems of a specific type (e.g., df -t ext4 for ext4 filesystems). |
-x [type] |
Excludes filesystems of a specific type (e.g., df -x tmpfs to exclude tmpfs filesystems). |
--total |
Produces a grand total at the end of the output, which is helpful in summarizing. |
-i |
Shows inode information instead of block usage, useful for inode-based monitoring. |
-k |
Displays the disk usage in 1024-byte blocks, the default setting. |
-l |
Limits the output to local filesystems only, omitting remote ones. |
--sync |
Ensures the data is up to date by invoking a sync before getting the usage data. |
--help |
Displays help and exit. |
--version |
Outputs version information and exit. |
Frequently Asked Questions about the df Command
What does the df command do in Linux?
The df command in Linux is used to display the amount of available and used disk space on all mounted filesystems. It shows details like total space, space used, space available, and the mount point of each filesystem.
How do I see disk space in GB in Linux?
To view disk space in GB (gigabytes) or other human-readable formats like MB (megabytes), use the -h option with the df command:
$ df -h
This will display the disk space in a format that’s easier to read and understand.
Can df show the type of filesystem?
Yes, the -T option with the df command displays the type of each filesystem:
$ df -T
How do I exclude a specific filesystem type in the df output?
To exclude a specific filesystem type, use the -x option followed by the filesystem type. For example, to exclude tmpfs filesystems, use:
$ df -x tmpfs
Is there a way to see inode information instead of disk usage with df?
Yes, the -i option will display inode information instead of block usage:
$ df -i
This is particularly useful when you need to monitor inode usage instead of disk space.
How can I get a summary of total disk space with the df command?
You can get a summary of total disk space used and available by using the --total option:
$ df --total
This will append a grand total line at the end of the output.
Does df provide real-time information?
To ensure that df provides the most current information, you can use the --sync option, which will perform a sync before fetching the data:
$ df --sync
This ensures the information reflects all recent changes to the filesystem.
Can I check disk space for a specific directory with df?
Yes, simply append the directory path to the df command:
$ df /path/to/directory
This will show the disk space usage for the filesystem where the specified directory is located.
Conclusion
The df command in Linux is an incredibly versatile and essential tool for managing and understanding disk space usage. As we explored, it provides a wide range of functionalities, from displaying disk space in a human-readable format to showing detailed filesystem types and inode information. The real-world examples and FAQs should equip you with the knowledge to effectively utilize df in various scenarios, whether you’re a system administrator, a developer, or a Linux enthusiast. Remember, the power of Linux lies in its flexibility and the depth of its command-line tools, and df is a shining example of this, offering insights into your system’s storage with simple yet powerful commands.
