Which directories are most important on Linux?

Linux

/ The root directory. All other directories are under this one.

/boot The kernel image, bootloader, and are stored here.

/etc Many of Linux's configuration files, including kernel module configuration.

/bin, /usr/bin, /usr/sbin Any of these "bin" directories will hold executable binaries (i.e. program commands).

/usr This holds most user applications, documentations, graphics, etc.

/lib, /usr/lib Important system libraries are stored here.

/root The system administrator's home directory.

/home All other home directories for all users are here. For example, a user's home directory might be /home/user.

/var Variable data, such as mail spools, log files, etc.

/tmp Temporary files created and used by applications.

/dev Devices are setup in this directory.

/mnt Mount points for filesystems, whether physical or virtual.

/proc This is a virtual directory which contains information about the kernel

/lost+found Files that might have been recovered after a bad shutdown or other event might show up in the lost and found.