Essential System Administration, 3rd Edition

Monitoring and Managing Disk Space Usage

This section looks at the tools available to monitor and track disk space usage. It then goes on to discuss ways of approaching a perennial administrative challenge: getting users to reduce their disk use.

Where Did It All Go?

The df -k command produces a report that describes all the filesystems, their total capacities, and the amount of free space available on each one (reporting sizes in KB). Here is the output from a Linux system:

File system    Kbytes   used     avail     capacity     Mounted on 
/dev/sd0a      7608     6369     478       93%          /
/dev/sd0g      49155    45224    0         102%         /corp

This output reports the status of two filesystems: /dev/sd0a, the root disk, and /dev/sd0g, the disk mounted at corp (containing all files and subdirectories underneath /corp). Each line of the report shows the filesystem’s name, the total number of kilobytes on the disk, the number of kilobytes in use, the number of kilobytes available, and the percentage of the filesystem’s storage that is in use. It is evident that both filesystems are heavily used. In fact, the /corp filesystem appears to be overfull.

As we’ve noted earlier, the operating system generally holds back some amount of space in each filesystem, allocatable only by the superuser (usually 10%, although Linux uses 5% by default). A filesystem may appear to use over 100% of the available space when it has tapped into this reserve.

The du -k command reports the amount of disk space used by all files and subdirectories underneath one or ...