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Understanding File Systems: A Comprehensive Overview and Functionality

What is File System

File System is a methods and structure of data that an operating system used to keep track the files and control the data are organized in the disk or partition.

File system logically defined the files in the disk by mentioned below :

  • Sharable - It can be accessed locally or by remote host.
  • unsharable - Only It can be accessed locally.
  • Variable - These files can able to change at any time such as documents.
  • Static - Static Binaries which is do not change without administrator permission.It used to execute the program to the user.

Types of File systems

Disk File Systems

Ability of disk storage media to randomly address data in a short amount of time.Additional considerations include the speed of accessing data following that initially requested and the anticipation that the following data may also be requested. This permits multiple users (or processes) access to various data on the disk without regard to the sequential location of the data. Some disk file systems are journaling file systems or versioning file systems.

Here are some of Disk File Systems are :

  • FAT (FAT12, FAT16, FAT32),
  • exFAT,
  • NTFS,
  • HFS and HFS+, HPFS,
  • UFS,
  • ext2, ext3, ext4,
  • XFS,
  • btrfs,
  • ISO 9660,
  • Files-11,
  • Veritas File System,
  • VMFS,
  • ZFS,
  • ReiserFS and UDF.

ISO 9660 and Universal Disk Format (UDF) are two common formats that target Compact Discs, DVDs and Blu-ray discs.

Flash File Systems

A flash file system considers the special abilities, performance and restrictions of flash memory devices. Frequently a disk file system can use a flash memory device as the underlying storage media but it is much better to use a file system specifically designed for a flash device.

Tape File Systems

A tape file system is a file system and tape format designed to store files on tape in a self-describing form. Magnetic tapes are sequential storage media with significantly longer random data access times than disks, posing challenges to the creation and efficient management of a general-purpose file system.

In a disk file system there is typically a master file directory, and a map of used and free data regions. Any file additions, changes, or removals require updating the directory and the used/free maps. Random access to data regions is measured in milliseconds so this system works well for disks.

Database file systems

Another concept for file management is the idea of a database-based file system. Instead of, or in addition to, hierarchical structured management, files are identified by their characteristics, like type of file, topic, author, or similar rich metadata.

Transactional file systems

Some programs need to update multiple files "all at once". For example, a software installation may write program binaries, libraries, and configuration files. If the software installation fails, the program may be unusable. If the installation is upgrading a key system utility, such as the command shell, the entire system may be left in an unusable state.

Transaction processing introduces the isolation guarantee, which states that operations within a transaction are hidden from other threads on the system until the transaction commits, and that interfering operations on the system will be properly serialized with the transaction. Transactions also provide the atomicity guarantee, ensuring that operations inside of a transaction are either all committed or the transaction can be aborted and the system discards all of its partial results. This means that if there is a crash or power failure, after recovery, the stored state will be consistent. Either the software will be completely installed or the failed installation will be completely rolled back, but an unusable partial install will not be left on the system.

Journaling file systems are one technique used to introduce transaction-level consistency to file system structures. Journal transactions are not exposed to programs as part of the OS API; they are only used internally to ensure consistency at the granularity of a single system call.

Network File Systems

A network file system is a file system that acts as a client for a remote file access protocol, providing access to files on a server. Programs using local interfaces can transparently create, manage and access hierarchical directories and files in remote network-connected computers.

Examples of network file systems include clients for the

  • NFS,
  • AFS,
  • SMB protocols,

And file-system-like clients for

  • FTP
  • WebDAV.

Shared disk file systems

A shared disk file system is one in which a number of machines (usually servers) all have access to the same external disk subsystem (usually a SAN). The file system arbitrates access to that subsystem, preventing write collisions.

Examples include

  • GFS2 from Red Hat,
  • GPFS from IBM,
  • SFS from DataPlow,
  • CXFS from SGI and
  • StorNext from Quantum Corporation.

Special file systems

A special file system presents non-file elements of an operating system as files so they can be acted on using file system APIs. This is most commonly done in Unix-like operating systems, but devices are given file names in some non-Unix-like operating systems as well.

Device file systems

A device file system represents I/O devices and pseudo-devices as files, called device files. Examples in Unix-like systems include devfs and, in Linux 2.6 systems, udev. In non-Unix-like systems, such as TOPS-10 and other operating systems influenced by it, where the full filename or pathname of a file can include a device prefix, devices other than those containing file systems are referred to by a device prefix specifying the device, without anything following it.

Other special file systems

  • In the Linux kernel, configfs and sysfs provide files that can be used to query the kernel for information and configure entities in the kernel.

  • procfs maps processes and, on Linux, other operating system structures into a filespace.

Linux File System Hierarchy

  • /boot/ - Directory contains static files required to boot the system such as kernel.

  • /dev/ - Directory contains the device nodes that either represent devices that are attached to the system or virtual devices that are provided by the kernel.The udev dameon takes care of creating and removing all these device node on this directory.

  • /etc/ - Reserved for configuration files that are required to the local machine.

  • /lib/ - Directory should contain the libraries needed to execute binaries are located on /bin/ and /sbin/. It is necessary to executes the commands within the root file system.

  • /media/ - Directory should used as mount point for removal media such as DVD-ROM or USB storage media stick.

  • /mnt/ - Directory reserved for temporary mounted file systems.

  • /opt/ - Directory to hold storage for most of application packages.It hold the manual files,binaries etc,.

  • /proc/ - Contains special files that either extract information from or send information to the kernel.for example it contain system memory,cpu information and other hardware information etc.

  • /bin/ - All the executable binary programs (file) required during booting, repairing, files required to run into single-user-mode, and other important, basic commands viz., cat, du, df, tar, rpm, wc, history, etc.

  • /sbin/ - Contains System binaries by the root user.It is used at boot time. It is essential for booting,restoring,recovering,repairing the system.

  • /srv/ - Directory contains site-specific data served by your system.It gives users the location of data files for particular service.

  • /sys/ - It contains the information about device similarly held in /proc/ directory. and also it utilizes the new systfs virtual file system specific to the 2.6 kernel.

  • /usr/ - Directory for the user level accessing files for configuration,binaries,libraries.And it contain the files that can shared across multiple machines.

  • /var/ - Directory for any programs to write logs or any other data need to stored by the programs.

Filesystem comparison

FS Name Year Introduced Original OS Max File Size Max FS Size Journaling
FAT16 1983 MSDOS V2 4GB 16MB to 8GB N
FAT32 1997 Windows 95 4GB 8GB to 2TB N
HPFS 1988 OS/2 4GB 2TB N
NTFS 1993 Windows NT 16EB 16EB Y
HFS+ 1998 Mac OS 8EB ? N
UFS2 2002 FreeBSD 512GB to 32PB 1YB N
ext2 1993 Linux 16GB to 2TB4 2TB to 32TB N
ext3 1999 Linux 16GB to 2TB4 2TB to 32TB Y
ReiserFS3 2001 Linux 8TB8 16TB Y
ReiserFS4 2005 Linux ? ? Y
XFS 1994 IRIX 9EB 9EB Y
JFS ? AIX 8EB 512TB to 4PB Y
VxFS 1991 SVR4.0 16EB ? Y
ZFS 2004 Solaris 10 1YB 16EB N

Sizes Table

Size Equivant Size
Kilobyte - KB 1024 Bytes
Megabyte - MB 1024 KBs
Gigabyte - GB 1024 MBs
Terabyte - TB 1024 GBs
Petabyte - PB 1024 TBs
Exabyte - EB 1024 PBs
Zettabyte - ZB 1024 EBs
Yottabyte - YB 1024 ZBs

Creating a FileSystem

Before creating a filesystem make sure the disk which you need to create is already unmounted or not.If not then unmount the same.And kindly note down creating filesystem would lost of entire data on the disk.

  • fdisk -l

It would list down all the available devices on the system.get the disk partition name from this command.

  • umount /dev/sdb1

It should the un mount the hard disk from the system.

  • mkfs.vfat /dev/sdb1 -n DiskName

It should format the disk partition which is specified and make the filesystem.

  1. mkfs - mkfs is used to build a Linux filesystem on a device, usually a hard disk partition. The device argument is either the device name (e.g. /dev/hda1, /dev/sdb2), or a regular file that shall contain the filesystem. The size argument is the number of blocks to be used for the filesystem.

  2. vfat - Formats the drive to FAT32 as filesystem type.And other formats available are

    mkfs.bfs, mkfs.ext2, mkfs.ext3, mkfs.ext4, mkfs.minix, mkfs.msdos, mkfs.vfat, mkfs.xfs, mkfs.xiafs etc

  3. /dev/sdb1 - Disk partition name on the disk should going to build the filesystem.

  4. -n - Sets the volume name (label) of the filesystem. The volume name can be up to 11 characters long. The default is no label.DiskName is the name which you required for the filesystem.

  5. Optional Field.And it may vary depend upon the Filesystem.For Example Label option should be -L for NTFS Filesystem.

Important Files and Usage

  • /boot/vmlinuz : The Linux Kernel file.

  • /dev/hda : Device file for the first IDE HDD (Hard Disk Drive)

  • /dev/hdc : Device file for the IDE Cdrom, commonly

  • /dev/null : A pseudo device, that don’t exist. Sometime garbage output is redirected to /dev/null, so that it gets lost, forever.

  • /etc/bashrc : Contains system defaults and aliases used by bash shell.

  • /etc/crontab : A shell script to run specified commands on a predefined time Interval.

  • /etc/exports : Information of the file system available on network.

  • /etc/fstab : Information of Disk Drive and their mount point.

  • /etc/group : Information of Security Group.

  • /etc/grub.conf : grub bootloader configuration file.

  • /etc/init.d : Service startup Script.

  • /etc/lilo.conf : lilo bootloader configuration file.

  • /etc/hosts : Information of Ip addresses and corresponding host names.

  • /etc/hosts.allow : List of hosts allowed to access services on the local machine.

  • /etc/host.deny : List of hosts denied to access services on the local machine.

  • /etc/inittab : INIT process and their interaction at various run level.

  • /etc/issue : Allows to edit the pre-login message.

  • /etc/modules.conf : Configuration files for system modules.

  • /etc/motd : motd stands for Message Of The Day, The Message users gets upon login.

  • /etc/mtab : Currently mounted blocks information.

  • /etc/passwd : Contains password of system users in a shadow file, a security implementation.

  • /etc/printcap : Printer Information

  • /etc/profile : Bash shell defaults

  • /etc/profile.d : Application script, executed after login.

  • /etc/rc.d : Information about run level specific script.

  • /etc/rc.d/init.d : Run Level Initialisation Script.

  • /etc/resolv.conf : Domain Name Servers (DNS) being used by System.

  • /etc/securetty : Terminal List, where root login is possible.

  • /etc/skel : Script that populates new user home directory.

  • /etc/termcap : An ASCII file that defines the behaviour of Terminal, console and printers.

  • /etc/X11 : Configuration files of X-window System.

  • /usr/bin : Normal user executable commands.

  • /usr/bin/X11 : Binaries of X windows System.

  • /usr/include : Contains include files used by ‘\ c\ ‘ program.

  • /usr/share : Shared directories of man files, info files,etc.

  • /usr/lib : Library files which are required during program compilation.

  • /usr/sbin : Commands for Super User, for System Administration.

  • /proc/cpuinfo : CPU Information

  • /proc/filesystems : File-system Information being used currently.

  • /proc/interrupts : Information about the current interrupts being utilised currently.

  • /proc/ioports : Contains all the Input/Output addresses used by devices on the server.

  • /proc/meminfo : Memory Usages Information.

  • /proc/modules : Currently using kernel module.

  • /proc/mount : Mounted File-system Information.

  • /proc/stat : Detailed Statistics of the current System.

  • /proc/swaps : Swap File Information.

  • /version : Linux Version Information.

  • /var/log/lastlog : log of last boot process.

  • /var/log/messages : log of messages produced by syslog daemon at boot.

  • /var/log/wtmp : list login time and duration of each user on the system currently.

Last update: June 17, 2023 21:48:54
Created: June 17, 2023 21:48:54

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