Understanding Linux Directory Structure: A Complete Guide to /bin, /etc, /usr, and More

Linux Directory Structure Overview

The Linux filesystem is organized into several top‑level directories, each serving a specific purpose. Below is a concise description of the most important ones.

/bin: binary executable commands.

/dev: device special files.

/etc: system management and configuration files.

/etc/rc.d: startup configuration files and scripts.

/home: user home directories (e.g., /home/user).

/lib: shared libraries (similar to Windows .dll files).

/sbin: system administration commands.

/tmp: temporary files used by programs.

/root: root (superuser) home directory.

/mnt: temporary mount point for other filesystems.

/lost+found: holds orphaned files after an abnormal shutdown.

/proc: virtual directory exposing kernel and system information.

/var: variable data such as logs and spools.

/usr: largest hierarchy containing most applications and files, with subdirectories like /usr/bin, /usr/sbin, /usr/lib, /usr/include, /usr/share, /usr/local, etc.

Typically the root filesystem should remain small because most files rarely change; only essential boot files (e.g., /vmlinuz) reside there. All other files are placed in subdirectories.

1. /bin Directory

/bin contains essential binary commands required for system boot and for regular users after boot.

2. /sbin Directory

/sbin is similar to /bin but primarily holds binaries used by system administrators; regular users may execute them when permitted.

3. /etc Directory

/etc stores various system configuration files, including user information (/etc/passwd), initialization scripts (/etc/rc), and many network configuration files.

4. /root Directory

/root is the home directory of the superuser.

5. /lib Directory

/lib holds shared libraries required by programs in the root filesystem, reducing duplication and saving space.

6. /lib/modules Directory

/lib/modules contains loadable kernel modules needed for hardware drivers and other core functionality.

7. /dev Directory

/dev contains device files that provide access to hardware devices (e.g., /dev/mouse, /dev/console).

8. /tmp Directory

/tmp stores temporary data generated by programs at runtime; after boot, /var/tmp is often preferred for larger temporary files.

9. /boot Directory

/boot holds bootloader files and kernel images. When many kernels are present, a separate filesystem may be used.

10. /mnt Directory

/mnt serves as a temporary mount point for manually mounting other filesystems (e.g., /mnt/cdrom, /mnt/ext2).

11. /proc, /usr, /var, /home Directories

These directories host additional filesystems: /proc is a virtual filesystem exposing kernel data; /usr contains read‑only application files; /var holds variable data; /home stores user data.

Each machine has a root filesystem containing boot files and tools needed for single‑user mode, system repair, and backup restoration.

/etc File System Details

/etc includes many important configuration files:

/etc/rc or /etc/rc.d or /etc/rc?.d – startup scripts.

/etc/passwd – user database.

/etc/fdprm – floppy parameters.

/etc/fstab – filesystems to mount at boot.

/etc/group – group information.

/etc/inittab – init configuration.

/etc/issue – pre‑login message.

/etc/magic – file command database.

/etc/motd – message of the day.

/etc/mtab – currently mounted filesystems.

/etc/shadow – shadow password file (more secure).

/etc/login.defs – login command configuration.

/etc/printcap – printer capabilities.

/etc/profile, /etc/csh.login, /etc/csh.cshrc – global shell environment.

/etc/securetty – list of terminals allowed for root login.

/etc/shells – list of valid login shells.

/etc/termcap – terminal capability database.

/dev File System Details

/dev provides device files for hardware access. Common entries include:

/dev/console – system console.

/dev/hd* – IDE hard‑disk partitions.

/dev/sd* – SCSI disk partitions.

/dev/fd0 – floppy drive.

/dev/st – SCSI tape drive.

/dev/tty* – virtual consoles.

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

/dev/ttys – serial ports (e.g., COM1).

/dev/cua* – serial ports for modems.

/dev/null – null device (discards all data).

/usr File System Details

/usr is a large filesystem containing most user programs and data. Important subdirectories include:

/usr/x11r6 – X Window system binaries and files.

/usr/bin – most user commands.

/usr/sbin – system administration commands.

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

/usr/include – C header files.

/usr/lib – shared libraries and package configuration.

/usr/local – locally installed software.

/var File System Details

/var stores data that changes frequently, such as logs, spools, and temporary files. Key subdirectories:

/var/catman – pre‑formatted manual pages.

/var/lib – variable state information.

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

/var/lock – lock files.

/var/log – system and application logs.

/var/run – runtime information (e.g., /var/run/utmp).

/var/spool – spool directories for mail, news, printers, etc.

/var/tmp – larger temporary files.

/proc File System Details

/proc is a pseudo‑filesystem exposing kernel and process information. Notable entries include:

/proc/[pid] – information about a specific process.

/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 ports in use.

/proc/kcore – physical memory image.

/proc/kmsg – kernel messages.

/proc/loadavg – system load average.

/proc/meminfo – memory usage.

/proc/modules – loaded kernel modules.

/proc/net – network protocol status.

/proc/self – symbolic link to the calling process's /proc entry.

/proc/stat – various system statistics.

/proc/uptime – system uptime.

/proc/version – kernel version.

Additional directories such as /usr/local and /opt are used for manually installed software and large third‑party packages respectively.