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File System and Directory Structure in Linux

File System and Directory Structure in Linux. What is File System. In a computer, a file system is the way in which files are named and where they are placed logically for storage and retrieval.

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File System and Directory Structure in Linux

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  1. File System and Directory Structure in Linux

  2. What is File System • In a computer, a file system is the way in which files are named and where they are placed logically for storage and retrieval. • Sometimes the term refers to the part of an operating system or an added-on program that supports a file system. Examples of such add-on file systems include the Network File System (NFS).

  3. logical file structure physical representation on disk

  4. File System • File systems specify conventions for naming files. These conventions include the maximum number of characters in a name, which characters can be used, and, in some systems, how long the file name suffix can be. A file system also includes a format for specifying the path to a file through the structure of directories.

  5. Linux File System • Ext2: This is like UNIX file system. • Ext3: It is ext2 filesystem with enhancement. • Isofs (iso9660): Used by CDROM file system. • Sysfs: It is a ram-based filesystem initially based on ramfs. It is use to exporting kernel objects so that end user can use it easily. • Procfs: The proc file system acts as an interface to internal data structures in the kernel For example you can find out cpuinfo with following command:

  6. Inside File System • User Data • Meta Data

  7. Linux Directory Structure • The Directory Structure in Unix & Linux are a unified Directory Structure where in all the directories are unified under the "/" Root file system. Irrespective of where the File System is physically mounted all the directories are arranged hierarchically under the Root file system.

  8. 1. / – Root • Every single file and directory starts from the root directory. • Only root user has write privilege under this directory.

  9. 2. /bin – User Binaries • Contains binary executables. • Common linux commands you need to use in single-user modes are located under this directory. • For example: ps, ls, ping, grep, cp.

  10. 3. /sbin – System Binaries • Just like /bin, /sbin also contains binary executables. • But, the linux commands located under this directory are used typically by system administrator, for system maintenance purpose. • For example: iptables, reboot, fdisk, ifconfig,

  11. 4. /etc – Configuration Files • Contains configuration files required by all programs. • This also contains startup and shutdown shell scripts used to start/stop individual programs. • For example: /etc/resolv.conf, /etc/logrotate.conf

  12. 5. /dev – Device Files • Contains device files. • These include terminal devices, usb, or any device attached to the system. • For example: /dev/tty1, /dev/usbmon0

  13. 6. /proc – Process Information • Contains information about system process. • This filesystemcontains information about running process. 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

  14. 7. /var – Variable Files • varstands for variable files. • Content of the files that are expected to grow can be found under this directory. • This includes — system log files (/var/log); packages and database files (/var/lib); emails (/var/mail); print queues (/var/spool); lock files (/var/lock); temp files needed across reboots (/var/tmp);

  15. 8. /tmp – Temporary Files • Directory that contains temporary files created by system and users. • Files under this directory are deleted when system is rebooted.

  16. 9. /usr – User Programs • Home directories for all users to store their personal files. • For example: /home/john

  17. 11. /boot – Boot Loader Files • Contains boot loader related files. • Grub files are located under /boot • For example: initrd.img-2.6.32-24-generic, vmlinuz-2.6.32-24-generic

  18. 12. /lib – System Libraries • Contains library files that supports the binaries located under /bin and /sbin • Library filenames are either ld* or lib*.so.* • For example: ld-2.11.1.so, libncurses.so.5.7

  19. 13. /opt – Optional add-on Applications • opt stands for optional. • Contains add-on applications from individual vendors. • add-on applications should be installed under either /opt/ or /opt/ sub-directory.

  20. 14. /mnt – Mount Directory • Temporary mount directory where sysadmins can mount filesystems.

  21. Inode • The inode (index node) is a fundamental concept in the Linux and UNIX file system. Each object in the file system is represented by an inode.

  22. File Information • File type (executable, block special etc)=> Permissions (read, write etc)=> Owner=> Group=> File Size=> File access, change and modification time (remember UNIX or Linux never stores file creation time, this is favorite question asked in UNIX/Linux sys admin job interview)=> File deletion time=> => Access Control List (ACLs)

  23. Inode • All the above information stored in an inode. In short the inode identifies the file and its attributes (as above) . Each inode is identified by a unique inode number within the file system. Inode is also know as index number.

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