how to use chmod command 777 in linux

The chmod command in Linux is used to change the permissions of files or directories. It stands for “change mode” and is a fundamental command for managing access control in Linux systems.

In Linux, file permissions are represented by three sets of permissions:

  • Owner Permissions: These apply to the owner of the file or directory.
  • Group Permissions: These apply to the group associated with the file or directory.
  • Other Permissions: These apply to everyone else.

Each set of permissions consists of three bits, which can be represented as r (read), w (write), and x (execute). So, a permission setting might look like “rwxr-x—“, where the first triplet represents the owner’s permissions, the second triplet represents the group permissions, and the third represents other permissions.

Here’s how you can use the chmod command to set file permissions:

Symbolic Mode: This is a more human-readable way to change permissions.

  • who: Specifies whose permissions to change. It can be one or more of the following:
    • u for the user/owner.
    • g for the group.
    • o for others.
    • a for all (equivalent to ugo).
  • (+|-|=): Indicates whether to add (+), remove (-), or set (=) permissions.
  • permission: Specifies the permission to add, remove, or set.
  • file/directory: The file or directory whose permissions you want to modify.

For example:

chmod u+x file.txt // Adds execute permission for the owner of file.txt
chmod go-w file.txt // Removes write permission for group and others from file.txt
chmod a=rw file.txt // Sets read and write permissions for all (owner, group, and others) on file.txt.

Numeric Mode: This method uses octal numbers to represent permissions.
  • chmod [mode] file/directory
  • mode: A numeric value representing the permission settings. Each digit in the mode represents a triplet of permissions (read, write, execute) for owner, group, and others, respectively.
    • 4 for read permission.
    • 2 for write permission.
    • 1 for execute permission.
    • You sum these values to represent different combinations. For example, 7 means read, write, and execute permissions, 6 means read and write, 5 means read and execute, and so on.

file/directory: The file or directory whose permissions you want to modify.

For example:

chmod 755 file.txt // Gives read, write, and execute permissions to the owner, and read and execute permissions to the group and others.
chmod 640 file.txt // Gives read and write permissions to the owner, and read permissions to the group, with no permissions for others.

These are the basic ways you can use chmod to set file permissions in Linux.

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