The df (disk free) command is the standard Unix/Linux utility for reporting file system disk space usage. It provides a high-level overview of all mounted file systems, showing the total size, used space, available space, and use percentage. The -h (human-readable) flag formats these sizes in an easily understandable way (e.g., KB, MB, GB). This command is the primary tool for quickly verifying overall disk usage levels when diagnosing storage issues on a system like the IBM QRadar appliance, which is built on a Linux-based operating system.

ls -laF: Lists the contents and attributes of files within a directory, not the overall filesystem usage.

lsof -h: Lists files that are currently open by processes; it does not report on disk capacity or usage.

du -h: Summarizes disk usage for specific files and directories, which is useful for finding what is using space, but not for an initial overview of all filesystems.

1. Official Vendor Documentation: In the IBM Security QRadar SIEM documentation, the df -h command is the specified method for checking disk partition usage during troubleshooting. For example, when addressing disk space issues on the /store partition.

Source: IBM. (2023). IBM Security QRadar SIEM Administration Guide (Version 7.5.0). Section: "Troubleshooting system health and performance," Subsection: "Disk space issues." (Note: Specific page numbers vary by document version, but the command is standard in troubleshooting procedures for disk space).

2. University Courseware: Reputable university computer science courses covering operating systems or system administration explicitly teach df for checking filesystem capacity.

Source: Massachusetts Institute of Technology (MIT). (2020). The Missing Semester of Your CS Education. Lecture 2: Shell Tools and Scripting. The course materials differentiate the use of df (for filesystem overview) and du (for directory-specific usage). Available at: https://missing.csail.mit.edu/2020/shell-tools/

3. Official Vendor Documentation (Linux): As QRadar appliances run on Red Hat Enterprise Linux (RHEL), the official RHEL documentation is an authoritative source. The df command is documented as the tool for reporting file system disk space usage.

Source: Red Hat, Inc. (2023). RHEL 8 Managing storage devices. Chapter 2, Section 2.6. "Displaying file system information." The documentation details the usage of df and its options, including -h.