[#linux]
In Linux/Unix operating system everything is a file even directories are files, files are files, and devices like mouse, keyboard, printer, etc are also files. Here we are going to see the Directory Structure in Linux. On Windows the capitalization is not important, but Linux and Mac are both case sensitive. In filesystems, we use the double dot (..) to access the parent directory, whereas the single dot (.) represents the current directory.
Primary hierarchy root and root directory of the entire file system hierarchy.
- Every single file and directory start from the root directory.
- The only root user has the right to write under this directory.
- /root is the root user’s home directory, which is not the same as /
Essential command binaries that need to be available in single-user mode; for all users, e.g., cat, ls, cp.
- Contains binary executables.
- Common linux commands you need to use in single-user modes are located under this directory.
- Commands used by all the users of the system are located here e.g. ps, ls, ping, grep, cp
Boot loader files, e.g., kernels, initrd.
Essential device files, e.g., /dev/null.
- These include terminal devices, usb, or any device attached to the system.
- Example: /dev/tty1, /dev/usbmon0
Host-specific system-wide configuration files.
- Contains configuration files required by all programs.
- This also contains startup and shutdown shell scripts used to start/stop individual programs.
- Example: /etc/resolv.conf, /etc/logrotate.conf.
Users’ home directories, containing saved files, personal settings, etc.
- Home directories for all users to store their personal files.
- example: /home/kishlay, /home/kv
Libraries essential for the binaries in /bin/ and /sbin/.
- Library filenames are either ld* or lib*.so.*
- Example: ld-2.11.1.so, libncurses.so.5.7
Mount points for removable media such as CD-ROMs (appeared in FHS-2.3).
- Temporary mount directory for removable devices.
- Examples, /media/cdrom for CD-ROM; /media/floppy for floppy drives; /media/cdrecorder for CD writer
Temporarily mounted filesystems.
- Temporary mount directory where sysadmins can mount filesystems.
Optional application software packages.
- Contains add-on applications from individual vendors.
- Add-on applications should be installed under either /opt/ or /opt/ sub-directory.
Essential system binaries, e.g., fsck, init, route.
- Just like /bin, /sbin also contains binary executables.
- The linux commands located under this directory are used typically by system administrators, for system maintenance purposes.
- Example: iptables, reboot, fdisk, ifconfig, swapon
Site-specific data served by this system, such as data and scripts for web servers, data offered by FTP servers, and repositories for version control systems.
- srv stands for service.
- Contains server specific services related data.
- Example, /srv/cvs contains CVS related data.
Temporary files. Often not preserved between system reboots and may be severely size restricted.
- Directory that contains temporary files created by system and users.
- Files under this directory are deleted when the system is rebooted.
Secondary hierarchy for read-only user data; contains the majority of (multi-)user utilities and applications.
- Contains binaries, libraries, documentation, and source-code for second level programs.
- /usr/bin contains binary files for user programs. If you can’t find a user binary under /bin, look under /usr/bin. For example: at, awk, cc, less, scp
- /usr/sbin contains binary files for system administrators. If you can’t find a system binary under /sbin, look under /usr/sbin. For example: atd, cron, sshd, useradd, userdel
- /usr/lib contains libraries for /usr/bin and /usr/sbin
- /usr/local contains user’s programs that you install from source. For example, when you install apache from source, it goes under /usr/local/apache2
- /usr/src holds the Linux kernel sources, header-files and documentation.
Virtual filesystem providing process and kernel information as files. In Linux, it corresponds to a procs mount. Generally, automatically generated and populated by the system, on the fly.
- Contains information about system process.
- This is a pseudo filesystem that contains information about running processes. For example: /proc/{pid} directory contains information about the process with that particular pid.
- This is a virtual filesystem with text information about system resources. For example: /proc/uptime
| Configuration Files | Description |
|---|---|
| /etc/bashrc | It is used by bash shell that contains system defaults and aliases. |
| /etc/crontab | A shell script to run specified commands on a predefined time interval. |
| /etc/exports | It contains information on the file system available on the network. |
| /etc/fstab | Information of the Disk Drive and their mount point. |
| /etc/group | It is a text file to define Information of Security Group. |
| /etc/grub.conf | It is the grub bootloader configuration file. |
| /etc/init.d | Service startup Script. |
| /etc/lilo.conf | It contains lilo bootloader configuration file. |
| /etc/hosts | Information of IP and corresponding hostnames |
| /etc/hosts.allow | It contains a list of hosts allowed accessing services on the local machine. |
| /etc/host.deny | List of hosts denied accessing services on the local machine. |
| /etc/inittab | INIT process and their interaction at the various run levels. |
| /etc/issue | Allows editing the pre-login message. |
| /etc/modules.conf | It contains the configuration files for the system modules. |
| /etc/motd | It contains the message of the day. |
| /etc/mtab | Currently mounted blocks information. |
| /etc/passwd | It contains username, password of the system, users in a shadow file. |
| /etc/shadow | users passwords hashes. |
| /etc/printcap | It contains printer Information. |
| /etc/profile | Bash shell defaults. |
| /etc/profile.d | It contains other scripts like application scripts, executed after login. |
| /etc/rc.d | It avoids script duplication. |
| /etc/rc.d/init.d | Run Level Initialisation Script. |
| /etc/resolv.conf | DNS being used by System. |
| /etc/security | It contains the name of terminals where root login is possible. |
| /etc/skel | Script that initiates new user home directory. |
| /etc/termcap | An ASCII file that defines the behavior of different types of the terminal. |
| /etc/X11 | Directory tree contains all the conf files for the X-window System. |
| Virtual and Pseudo Process Related Files | Description |
|---|---|
| /proc/cpuinfo | CPU Information |
| /proc/filesystems | It keeps useful info about the processes that are currently running. |
| /proc/interrupts | it keeps the information about the number of interrupts per IRQ. |
| /proc/ioports | Contains all the Input and Output addresses used by devices on the server |
| /proc/meminfo | It reports the memory usage information. |
| /proc/modules | Currently using kernel module. |
| /proc/mount | Mounted File-system Information. |
| /proc/stat | It displays the detailed statistics of the current system. |
| /proc/swaps | It contains swap file information. |
| Log Files | Description |
|---|---|
| /var/log/lastlog | It stores user’s last login info. |
| /var/log/syslog | Shows general messages and info regarding the system. Basically a data log of all activity throughout the global system. |