chmod [mode] [file]: Changes the permission mode of a file/directory.chmod [options] [mode] [file]: Changes the permission mode of a file/directory and specifies the corresponding parameters. Common options are as follows:c: Displays the action taken only if the file's permission is actually changed.f: Suppresses error messages.v: Displays detailed processing information for permission changes.R: Processes all files and subdirectories in the specified directory recursively.[ugoa...][[+-=][rwxXstugo...]...][,...] where:u represents the file owner, g represents the user group to which the file owner belongs, o represents other users, and a represents all users.+ adds permission, ``removes permission, and= sets permission.r represents read permission, w represents write permission, x represents execute permission, and X represents execute permission only when the file is a directory or at least one user already has execute permission for the file.s represents setting the SUID or SGID bit, t represents setting the sticky bit, u represents that the permission is only valid for the file owner, g represents that the permission is only valid for the user group to which the file belongs, and o represents that the permission is only valid for other users.chmod u+x [file]: Adds execute permission for file owner.chmod a=rw [file]: Sets read/write permission for all users.chmod 755 [dir]: Sets the directory's permission to rwxr-xr-x, where the file owner has read, write, and execute permission, and other users have read and execute permission.chmod -R u+w [dir]: Recursively adds write permission for the file owner for the directory and all files in its subdirectories.chmod u+x [file], Adds execute permission for file owner.chmod a=rw [file], Sets read/write permission for all users.chmod 755 [dir], Sets the directory's permission to rwxr-xr-x, where the file owner has read, write, and execute permission, and other users have read and execute permission.chmod -R u+w [dir], Recursively adds write permission for the file owner for the directory and all files in its subdirectories.