CNT-2311-Chapter 4 Notes
File Naming and Wildcard Expansion Rules
Linux file names can contain uppercase/lowercase letters, numbers, and most punctuation and control characters.
(.) Files refer to the current directory
(..) Files refer to the parent directory
File names are case-sensitive.
Three classes of wildcards
- ?: Stands in for another single character
- *: Matches any character or any set of characters
- : Normally match any character in a set. Also possible to specify a range of values
ls: displays the names of files in a directory. Short for “list”.
cp: Copies a file.
mv: Move files and directories from one place to another and rename them.
rm: Remove command used to delete files.
touch: Modifies file time stamps.
tar: Stands for tape archiver. This utility is used to archive data to other media.
cpio: Used to restore data. There are 3 modes.
- Copy-out mode: Creates an archive and copies files into it.
- Copy-in mode: Extracts data from an existing archive.
- Copy-pass mode: Combines the copy-out and copy-in modes, enabling you to copy a directory from one location to another.
dd: Low level copying program normally useful with partitions.
mkdir: Creates a directory
rmdir: Destroys a directory
ln: used to create links.
There are two types of links:
- Hard links: create two directory entries that point to the same file.
- Soft links: Sometimes referred to as symbolic links. Soft links are a separate file whose content points to the linked-to file.
Managing File Ownership
Security is built on file ownership and file permission.
Whenever a file is created it’s assigned an owner.
ls-l : shows the permissions on a file
chown: used to change a file's ownership and may only be used by root
chgrp: change a file's group
X: execute only if the file is a directory or already has execute permission
s: SUID or SGID
- SUID: Set user id option used with executable files to run with permission of the owner of the file
- SGID: Set group ID. Sets the group of the running program to the group of the file.
t: sticky bit which is used to protect files from being deleted by those who don’t own the files
File Locating Commands
find [path…] [expression…]
- Very flexible and likely to succeed
- Tends to be slow
- example of an expression is –name, used to match exact file names
- Typically faster than find
- Only searches by file names
- Likely to return false alarms becuase any file containing the name that is searched for will come up
- Searches for files in a restricted set of locations
- Returns filenames that begin with what you type in
- Searches your path for what you type in
- Lists the path to first match it finds
- Tells you how a command you type will be interpreted
- It might say a command is a built-in, external, or alias command.