/ The root directory, the top-level directory in the FHS. All other directories are subdirectories of root, which is always mounted on some partition. All directories that are not mounted on a separate partition are included in the root directory’s partition.
/bin Essential command line utilities. Should not be mounted separately; otherwise, it could be difficult to get to these utilities when using a rescue disk.
/boot Includes Linux startup files, including the Linux kernel. Can be small; 16MB is usually adequate for a typical modular kernel. If you use multiple kernels, such as for testing a kernel upgrade, increase the size of this partition accordingly.
/etc Most basic configuration files.
/dev Hardware and software device drivers for everything from floppy drives to terminals. Do not mount this directory on a separate partition.
/home Home directories for almost every user.
/lib Program libraries for the kernel and various command line utilities. Do not mount this directory on a separate partition.
/mnt The mount point for removable media, including floppy drives, CD-ROMs, and Zip disks.
/opt Applications such as WordPerfect or StarOffice.
/proc Currently running kernel-related processes, including device assignments such as IRQ ports, I/O addresses, and DMA channels.
/root The home directory of the root user.
/sbin System administration commands. Don't mount this directory separately.
/tmp Temporary files. By default, Red Hat Linux deletes all files in this directory periodically.
/usr Small programs accessible to all users. Includes many system administration commands and utilities.
/var Variable data, including log files and printer spools.