In Linux (and whatever else; don't fuck with me!), the directory for user and system administration binaries. The directory usually contains programs primarily used for system administration, but can also have user-specific binaries. The commands inside the directory are required for single-user mode (maintenance mode).

Any programs not needed in the root partition should be stored instead in /usr/bin (things like mail and sendmail). Depending on the distribution, restoration commands such as tar, gzip, gunzip, and zcat should be in this directory, but are not required.

Required commands: