Unlocking Linux: What Every Directory in the File System Means

/bin directory

The /bin directory holds essential binary executables needed for system boot and for ordinary users; these are binary (binary‑) files that form the core command set.

/sbin directory

The /sbin directory is similar to /bin but primarily contains administrative binaries used by the system administrator; regular users may run them when permitted.

/etc directory

/etc stores system configuration files, such as /etc/passwd (user database), /etc/rc or /etc/rc.d (startup scripts), /etc/fdprm (floppy parameters), /etc/fstab (filesystem mount table), /etc/group (group definitions), /etc/inittab (init configuration), /etc/issue (login banner), /etc/magic (file type definitions), /etc/motd (message of the day), /etc/mtab (currently mounted filesystems), /etc/shadow (shadow passwords), /etc/login.defs (login defaults), /etc/printcap (printer capabilities), /etc/profile, /etc/csh.login, /etc/csh.cshrc (global shell environments), /etc/securetty (secure terminals), /etc/shells (allowed shells), and /etc/termcap (terminal capabilities).

/root directory

/root is the home directory of the superuser (root).

/lib directory

/lib contains shared libraries needed by programs in the root filesystem, allowing code reuse and reducing executable size.

/lib/modules directory

/lib/modules holds loadable kernel modules, especially those required for system recovery such as network and filesystem drivers.

/dev directory

/dev provides device files that represent hardware devices. Important entries include:

/dev/console – system console.

/dev/hd* – IDE hard‑disk partitions (e.g., /dev/hda, /dev/hda1).

/dev/sd* – SCSI disk partitions (e.g., /dev/sda).

/dev/fd* – floppy devices (e.g., /dev/fd0).

/dev/st* – SCSI tape devices.

/dev/tty* – virtual consoles (e.g., /dev/tty1).

/dev/pty* – pseudo‑terminals for remote logins.

/dev/ttys* – serial ports (e.g., /dev/ttyS0).

/dev/cua* – serial communication devices.

/dev/null – null device that discards all written data.

/tmp directory

/tmp stores temporary files created by programs during execution; for longer‑lived temporary data, /var/tmp is preferred.

/boot directory

/boot contains the bootloader files and kernel images; large numbers of kernels may be moved to a separate filesystem.

/mnt directory

/mnt is a mount point for temporarily mounting other filesystems, such as /mnt/dos, /mnt/ext, or /mnt/cdrom.

/usr directory

/usr is a large hierarchy for user‑installed applications and data. Key subdirectories include:

/usr/x11R6 – X Window system binaries and files.

/usr/x386 – X11R5 binaries.

/usr/bin – most user commands.

/usr/sbin – system administration commands.

/usr/man, /usr/info, /usr/doc – manual pages, GNU info documents, and other documentation.

/usr/include – C header files.

/usr/lib – shared libraries and some configuration files.

/usr/local – locally installed software and data.

/var directory

/var holds variable data that changes frequently, such as logs, spools, and temporary files. Important subdirectories include:

/var/catman – pre‑formatted manual pages.

/var/lib – state information for packages and services.

/var/local – variable data for locally installed programs.

/var/lock – lock files used to coordinate access to resources.

/var/log – log files for system and application events.

/var/run – runtime information such as /var/run/utmp.

/var/spool – spool directories for mail, print queues, etc.

/var/tmp – larger or longer‑lived temporary files.

/proc filesystem

/proc is a virtual filesystem that provides runtime kernel and process information. Notable entries include:

/proc/cpuinfo – CPU details.

/proc/devices – loaded device drivers.

/proc/dma – DMA channel usage.

/proc/filesystems – supported filesystems.

/proc/interrupts – interrupt usage.

/proc/ioports – I/O port allocation.

/proc/kcore – physical memory image.

/proc/kmsg – kernel messages.

/proc/ksyms – kernel symbol table.

/proc/loadavg – system load averages.

/proc/meminfo – memory usage.

/proc/modules – loaded kernel modules.

/proc/net – network protocol status.

/proc/self – symlink to the calling process's own /proc entry.

/proc/stat – various kernel statistics.

/proc/uptime – system uptime.

/proc/version – kernel version.