Table of Contents

• sudo
• Understanding Permissions
• Changing Permissions
• Executables
• Changing Owners

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sudo

• sudo stands for superuser do. It allows a permitted user to execute a command as the superuser or another user, as specified by the security policy.
• Common usage:

sudo command_name

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Understanding Permissions

The permissions of an individual file or directory are represented as a 10-character string:

• The first character indicates the type:

  • -: Regular file (e.g. -rwxrwxrwx)
  • d: Directory (e.g. drwxrwxrwx)

• The next 9 characters are grouped into three sets:

  • Owner permissions (first 3 characters)
  • Group permissions (next 3 characters)
  • Others permissions (last 3 characters)

Each set has:

• r – read
• w – write
• x – execute

Examples:

rwx  -> read, write, and execute
rw-  -> read and write only
r-x  -> read and execute only

To view permissions, use:

ls -l

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Changing Permissions

Use the chmod command (change mode) to set or modify file and directory permissions.

Example:

chmod -R u=rwx,g=,o= DIRECTORY

Explanation:

• -R: Apply changes recursively to contents
• u: user (owner)
• g: group
• o: others
• =: assign specified permissions
• rwx: read, write, execute
• g=, o=: remove all permissions from group and others

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Executables

Files with a .sh extension are shell scripts—text files that contain shell commands.

You can run a shell script by providing its path:

mydir/program.sh

If it’s in the current directory, use ./ to specify the path:

./program.sh

Before running, make sure the script is executable:

chmod +x program.sh

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Changing Owners

Use the chown command (change owner) to change the owner and/or group of a file or directory. Requires root privileges.

Syntax:

sudo chown new_owner:new_group filename

Example:

sudo chown adarsh:staff notes.txt

This changes the owner of notes.txt to adarsh and its group to staff.

To apply recursively:

sudo chown -R user:group directory/