When copying under linux, sometimes there will be an error of cp:omitting directory. For example, cp:omitting directory "bbs" means that there are directories under the bbs directory, which cannot be copied directly.
Solution: recursive copy Command: cp -r bbs ../backup/bbs Explanation: -r This option means recursion
Infer from one another: when deleting, there may also be a problem that the following files cannot be deleted. Also use -r to cascade delete
When chmod grants permissions, you can also use -R to cascade. Note that it is a capital R.