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Understanding Read, Write, and Execute Permissions

1. Basic Permissions:

• Read (r): Allows viewing the content of a file or listing the contents of a directory.
  • File: cat file displays content.
  • Directory: ls directory lists files.
• Write (w): Allows modifying the content of a file or adding/removing files in a directory.
  • File: echo "text" > file writes to the file.
  • Directory: touch newfile adds a new file.
• Execute (x): Allows running a file as a program or accessing a directory.
  • File: ./script.sh executes a script.
  • Directory: cd directory changes into the directory.

Permission Representation:

• File Permissions: Shown as -rwxr-xr--
  • rwx: Owner permissions
  • r-x: Group permissions
  • r--: Others permissions

Numeric Mode:

• Example: 755 represents rwxr-xr-x.

Special Permissions

1. Setuid (s):

• Usage: Executes a file with the privileges of the file owner.
• Set with: chmod u+s file
• Example: -rwsr-xr-x (Setuid bit set)

2. Setgid (s):

• Usage: Executes a file with the group’s privileges or sets group ownership on new files in a directory.
• Set with: chmod g+s directory
• Example: -rwxr-sr-x (Setgid bit set)

3. Sticky Bit (t):

• Usage: Ensures only the file owner can delete or rename their files in a directory.
• Set with: chmod +t directory
• Example: drwxrwxrwt (Sticky bit set)

These commands control who can read, write, or execute files and directories, and set special access rules.

Go back to topics page [[Linux Basics]].