Disk and Filesystem Commands

Before we talk too much about partitions and mount points it is important to understand that a Linux mount point can be anywhere you could put a directory.  While at the base of any Linux system there is a / directory, commonly called the root directory a partition may be mounted anywhere below that.  Here are some examples of common mount points and what you might find there:

Displaying File System Information

It is very common to have to examine disk use to determine where there is free space, where the disk may be nearing full and where you may need to add disk or move files.  One of the most essential commands used to examine disks is the df command.

The df command is used to display information about mounted file systems.  By default the df command will typically return disk information in kilobytes.  Since there can be variation on this default behavior it is often nice to use the ?k option which will force df to displays disk space usage in kilobytes as seen in this example:

$ df -k

Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/hdf1             18727836   2595832  15180656  15% /
/dev/hda1               101086      5945     89922   7% /boot
none                    128560         0    128560   0% /dev/shm

These results show that two file systems are mounted.  The Filesystem column of the output shows the path to the disk device which is currently mounted at the Mounted on location.  The 1K-blocks column displays the size of the entire partition while the Used and Available columns indicate the number of 1K blocks on that device used and available.  The Use% column will show what percentage of the disk is currently used and is the quickest way to identify disks which are getting full.

To get the display in a friendlier format, the ?h option can be used:

$ df -h

Filesystem            Size  Used Avail Use% Mounted on
/dev/hdf1              18G  2.5G   15G  15% /
/dev/hda1              99M  5.9M   88M   7% /boot
none                  126M     0  126M   0% /dev/shm

The  -h option will show output in the familiar gigabyte, megabyte or kilobyte (G, M or K respectively) scales.  This makes things more human readable, hence the h.

It is easy to see that the first file system is 18GB in size, with 2.5GB used and 15GB of available free space. It is mounted on the root (/) mount point.

The second file system is 99MB in size, with 5.9MB used and 88MB of available free space. It is mounted on the /boot mount point.

This output also shows a shared memory space of 126MB currently available (/dev/shm).

Creating a File System

Some file systems are created automatically during the Linux installation process.  For instance, when I set up a system with Fedora Core 2 (Red Hat) for this book, the installation tool detected the two disk drives and offered to automatically configure their partitions and setup a file system.

There are many different types of file systems. Microsoft Windows administrators are familiar with filesystems like FAT16, FAT32, and NTFS.  The comparable options on Linux are ext2, ext3, and Linux-swap.  The differences between these filesystem types are beyond the scope of this book.

During the lifetime of a Linux system it is not uncommon to want to add additional disk space to a system by adding disks or replace a current drive with a larger capacity.  Here are some of the most useful commands for setting up disks:

Note:  You will need root privileges to to perform most of these tasks.