Command Line – BusyBox » Linux Magazine

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BusyBox features a small footprint and speed, making it a popular choice for systems with limited resources.

BusyBox [1] is often described as a set of utilities. That description is not inaccurate, because BusyBox includes over 400 commands. However, what distinguishes BusyBox is how it organizes those commands. All the commands in BusyBox are sub-commands of the bare command and run in the Ash shell, a derivative of the Almquist Shell [2], long known for its speed and small size. With these advantages, BusyBox has become a popular choice for embedded systems, containers, and computers with limited resources. In addition, it is often used by those who want a faster command line, or by system administrators who want the added security of limiting the commands available to other users. While BusyBox is often described as a Swiss Army knife, it is more accurate to consider it a command-line shell and an alternative to Bash.

BusyBox was originally written in 1995 by Bruce Perens to provide a complete operating system on a single floppy disk. Since then, under successive maintainers and dozens of contributors, BusyBox has expanded from its role as a Debian tool to become a cross-platform tool and a standard wherever efficient use of memory is a priority. This continued popularity has made BusyBox a frequent target for violations of the GNU General Public License (GPL). In addition, the BusyBox project is known for its insistence on continuing to use GPLv2 rather than switching to GPLv3, a controversy that resulted in forks such as Toybox under different licenses; this was finally resolved by adopting a license that specifies only GPL 2.0 or later. At times, these licensing issues have threatened to overshadow everything else, but today BusyBox remains known for its versatility and usefulness.

BusyBox’s Structure

If you have spent any time in a Linux shell, BusyBox’s sub-commands will be familiar to you. Tar, permissions, grep, less – if you can name a command in Bash or most shells, the chances are you can find an identically named command in BusyBox. Despite being available on several operating systems, BusyBox openly adheres to common Unix standards and practices. However, there is one important difference: The BusyBox command often has fewer options than the same command in most shells. With simpler commands such as free, which shows a system’s memory usage, there may be no difference. By contrast, though, the grep search command in Bash contains over 40 options (the exact number depending on how sub-options are counted), but only 24 in BusyBox. Naturally, BusyBox includes the most common options, just as a desktop application often does. However, an advanced or specialist option may be missing in BusyBox. Sometimes, too, other applications may be hardwired to use the commands from the shell downloaded when a system is installed. As a result, some operations are difficult or impossible in BusyBox. Perhaps just as important, this means that regular man pages are not always useful in BusyBox. Instead, users must rely on BusyBox’s own man page, which is over 80 pages long and perhaps best used in a web browser, where searches are easier.

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