• RHEL supports seven types of files:
  • Regular
  • Directory
  • Block special device → Used by the OS to communicate with peripheral devices.
  • character special device → Used by the OS to communicate with peripheral devices.
  • symbolic link
  • named pipe → Used in IPC(Inter Process Communication)
  • socket → Used in IPC(Inter Process Communication)

Regular Files:

• Regular files may contain text or binary data. These files may be shell scripts or commands in the binary form. When you list a directory, all line entries for files in the output that begin with the hyphen character (-) represent regular files.
  • Example:
  • The - before the rw permission depicts that it is a regular file.
• file command: Returns the specific type of data that the file contains, in this case it’s ASCII text.
• stat command: It simply states that the file is a regular file.

Directory Files:

• Directories are logical containers that hold files and subdirectories.
• The letter “d” at the beginning of each line entry identifies the file as a directory.
• file command on /usr directory:
• stat command on /usr directory:

Block and character special device files:

• What are Device files? Each piece of hardware in the system has an associated file in the /dev directory that is used by the system to communicate with that device. This type of file is called a device file.
• Types of device files:
  • Block → On the initial with the letter b we can distinguish it’s Block device file.
  • Character/ raw → On the initial with the letter c we can distinguish it’s character device file.
• file command on both of the directories → /dev/console and /dev/nvme0n*
• stat command on both of the directories → /dev/console and /dev/nvme0n*

Important concepts related to device files(PAY ATTENTION):

Concept of major number:

Let’s elaborate the picture

• Every hardware device such as a disk, CD/DVD, printer, and terminal has an associated device driver loaded in the kernel. The kernel communicates with hardware devices through their respective device drivers. Each device driver is assigned a unique number called the major number, which the kernel uses to recognize its type.

Concept of Minor number:

• There may be more than one instance of the same device type in the system. In that case, the same driver is used to control all those instances. For example, ==SATA device driver controls all SATA hard disks and CD/DVD drives==. The kernel in this situation allots a minor number to each individual device within that device driver category to identify it as a unique device. This scheme applies to disk partitions as well. In short, a major number points to the device driver, and a minor number points to a unique device or partition that the device driver controls.

Practical example of major and minor numbers:

• Previously when we used the file command and ls -l on /dev/console and /dev/nvme0n* directories, we will analyze them again and identify where actually it shows the major and minor numbers:
  • ls -l output analyze:
    • The major number 5 is for character device files and it is reserved for tty and console related devices.
      • /dev/tty - (5,0)
      • /dev/console - (5,1)
      • /dev/ptmx - (5,2)
    • The major number 259 represents Block extended device files and it is dynamically assigned to NVME devices.

EXTRA MAJOR NUMBERS(for knowledge):

1. Major number 8 represents the block device driver for SATA disks.
2. Major number 253 denotes the driver for device mapper.
3. Major number 11 represents optical devices.

Symbolic links/ soft link/ symlink:

• It is considered a shortcut to another file or directory.
• When we will perform ls -l/ longlisting of files/directories, the initial letter will be l for a symlink plus an arrow will be pointing to the target link.
  • 
• file and stat command for additional information:
  • 

Compression and archiving:

• What is compression?
  • It is the process of grouping multiple files and then compress them together to save space.
• What is archiving?
  • They contain single file that further contains one or more compressed/uncompressed files along with metadata like folder structures.
  • The archiving technique mostly used for long-term backups and storages etc.

Using gzip and gunzip:

• The gzip command is used to create a compressed file of each of the specified files and it adds the .gz extension to each file for identification.
  • We will compress and decompress the file fstab →
    • First copy the file from /etc/fstab to the current working directory - Now use the gzip command to compress the file → - Check more info about the compressed file using the following command:

    • gzip -l fstab.gz
      

    • 
    • Decompress the file using the command gunzip →

Using bzip2 and bunzip2:

• They are same as gzip and gunzip . Instead bzip2 compress a file with the extension .bz2
  • bzip2 :
  • bunzip2 :

Using tar:

• The tar (tape archive) command is used to create, append, update, list, and extract files or an entire directory tree to and from a single file, which is called a tarball or tarfile. This command can be instructed to also compress the tarball after it has been created. Commands:

1. To create a tarball called /tmp/home.tar of the entire /home directory, use the -v option for verbosity and the -f option to specify the name of the archive file with the command, -c creates a tarball.

tar -cvf /tmp/home.tar /home

2. To create a tarball of selected files:

tar -cvf /tmp/files.tar /etc/passwd /etc/yum.conf

3. To append files located in the /etc/yum.repos.d directory to the existing tarball /tmp/files.tar:

tar -rvf /tmp/files.tar /etc/yum.repos.d

4. To list what files are included in the files.tar tarball:

tar -tvf /tmp/files.tar

5. To extract the files from the tarball

tar -xf /tmp/files.tar

6. tar also supports options to directly compress the target file while being archived using the gzip or bzip2 command: