Linux Command Line - Disk Usage and Disk Filesystem

2017-07-04
tutorial linux

du displays disk usage information and df displays disk filesystem information. These commands also work on Mac OS X.

Disk Usage

du <path> displays size of each subdirectory in the path and the total sum of the size of all directories in the path in bytes. du is equivalent to du ./.

du -h displays the data in human readable format. It round sizes up to their largest unit and the unit abbreviation: bytes B, kilobytes K, megabytes M, gigabytes G, etc.

du -sh provides the total size of the path in human readable format. It may be slow if there are many subdirectories.

Data sizes

  • 1 bit b
  • 1 byte B = 8 bits
  • 1 kilobyte KB (1024) = 1024 bytes
  • 1 megabyte MB (1024^2) = 1024 kilobytes
  • 1 gigabyte GB (1024^3) = 1024 gigabytes
  • 1 terabyte TB (1024^4) = 1024 gigbaytes

Disk Filesystem

df displays device name, block size, disk space, used disk space, available disk space and mount points.

df -h displays the same as above but in human readable format.

block

A sequence of bytes or bits of a particular length, the block size. Putting data into blocks is blocking and extracting data from a block is deblocking. It helps reduce overhead and speed up data streams.

mount

mount command instructs an operating system that a file system is ready for use. It associates a point in the file system (the mount point) to another file system. File systems, files, directories and devices (USB, CD-ROMs, DVDs, etc.) can be mounted.

umount dissociates a mount point from its filesystem.

device name

A device file is an interface for a device driver that appears in the file system as if it were an ordinary file. In Unix systems most devices appear as files in a virtual file system.

inode

A Unix data structure that describe objects in a file system like files and directories. It stores disk block location, owner and permissions data and time of last change, access and modification.

POSIX standards requires the following:

  • size of file in bytes
  • device id of the device the file belongs to
  • file owner’s user id
  • file’s group id
  • file mode
  • system and user flags
  • inode last modified, file content last modified and time last accessed
  • count of hard links pointing to the inode
  • pointers to the disk blocks that store the file’s contents