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The UNIX du Command - Part I

UNIX Disk Usage - Tracking Down Disk Space "Hogs"

To be successful at UNIX system administration, there are a number of inherent tasks that MUST be performed by the system administrator.  One of the primary inherent tasks is monitoring and managing disk space usage.

The system administrator needs to be proactive in regards to this responsibility (e.g., by setting up automated monitoring and notification programs), or may experience one or more of the following if a key filesystem becomes full:

· system slow-down
· users unable to log in
· a system crash

Even with an automated monitoring or notification solution in place, there may be times when the system administrator will have to be reactive in identifying disk space "hogs."  One of the most common tools for handling this is the UNIX du command.  (If it's not obvious, du stands for disk usage.)

The syntax for the du command is:

du   [OPTION...]   [DIRECTORY...]

The command will report the amount of disk space used by all of the files and sub-directories located beneath the directory specified with the DIRECTORY command argument.  The following example shows the du output for one particular system's /home directory:

# du /home
4          /home/jdoe/tmp/docs1
8          /home/jdoe/tmp
4          /home/jdoe/testdir1
4          /home/jdoe/testdir2
4          /home/jdoe/testdir3
4          /home/jdoe/docs
128      /home/jdoe
4          /home/wilbur/tmp/docs1
1036     /home/wilbur/tmp
4          /home/wilbur/testdir1
4          /home/wilbur/testdir2
4          /home/wilbur/testdir3
4          /home/wilbur/docs
1144     /home/wilbur
1276     /home

Notice that the results are listed by sub-directory.  Since there are only two non-system users on this server, it is easy to identify that wilbur is the largest consumer of disk space within the /home directory.  It can also be seen that files in wilbur's "tmp" sub-directory are consuming the largest amount of space under his home directory (/home/wilbur).

The total amount of space used by files and directories underneath /home in this example is 1,276 blocks.  The size of a block is typically 512 or 1,024 bytes, but each system's documentation should be consulted to determine the default size it uses.

Visually identifying heavy disk space users works fine if there are only a handful of users on a system, but how would one quickly accomplish this same task on a system with hundreds or thousands of users?
Read the NEXT article in this series to find out - The UNIX du Command - Tracking Down Disk Space "Hogs" - Part II