Display Post IDs

test.php

add_filter( 'manage_posts_columns', 'revealid_add_id_column', 5 );
add_action( 'manage_posts_custom_column', 'revealid_id_column_content', 5, 2 );


function revealid_add_id_column( $columns ) {
   $columns['revealid_id'] = 'ID';
   return $columns;
}

function revealid_id_column_content( $column, $id ) {
  if( 'revealid_id' == $column ) {
    echo $id;
  }
}