Linux Commands and Paths in Linux

Intro

Linux is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. System commands are a computer user’s instruction (not part of a program) that calls for action by the computer’s executive program. Most of the “commands” that we use on the Linux command line are in fact programs (which are stored as files) located typically in the /bin or /usr/bin directories. Take the cp command for instance. You can use the “which” command to determine where the cp program is located.

Basic commands and Paths

• What is the date?

  1

  $ date

• Let’s print something

  1	$ echo "Hello World"

• Paths: what are they

  1	$ echo $PATH

• Files and Paths

  1	$ which python

• Get Help

  1	$ man echo

  Get short help

  1	$ whatis echo

Navigating Paths

• Where am I in the structure?

  1

  $ pwd

• What’s in here?

  1

  $ ls

• OR prettier, what’s in here?

  1

  $ tree

• How to change to another directory?

  1	$ cd directory_name

• How do I move up the directory structure?

  1

  $ cd ..

• How do I move to my home directory?

  1

  $ cd ~

Files Creaing and Moving

• Create a file

  1	$ touch file_name

• Is the file there?

  1	$ ls -l file_name

• What’s in the file

  1	$ cat file_name

• What type of file is this

  1	$ file file_name

• Rename, Move this file to another directory

  1	$ mv original_file final_file

• Find the file

  1	$ ls -l final_file

• Copy the file (make a second copy)

  1	$ cp file_name new_file_name

• Cobble files (DO NOT Try this)

  1	$ cp file_name existing_file_name

• Combine multiple files into another

  1	$ cat file1 file2

• See the beginning of a file

  1	$ head file

• See the end of a file

  1	$ tail file

• Pause between each pageful of file

  1	$ less file

• Same thing (older)

  1	$ more file

Directories

• Create a directory

  1	$ mkdir dir1

• List the directory

  1	$ ls -al dir1

• Dot, dot dot, dash, and tilde

  1	$ cd . ; cd .. ; cd - ; cd ~

• Rename/Move a directory

  1	$ mv dir1 dir2

• Nest directories (be careful)

  1	$ mv dir2 dir3/

Removing files/directories

• Remove a file

  1	$ rm file1

• Remove an empty directory

  1	$ rmdir dir1

• Remove a directory and files in it (CAREFUL)

  1	$ rm -r dir1

• Remove a link. Careful with symlinks

  1	$ rm linkname

• Try to remove a file you don’t have permissions to

  1	$ rm linkname

Links

• Create a hard link to a file. This creates another path to the file contents.

  1	$ ln target linkname

• Create a symbolic link to a file or directory. This creates a link to the existing path, and not the file contents.

  1	$ ln -s target linkname

Ownership and Permissions

• Look at permissions and owners

  1	$ ls -l file

• Change owners, groups

  1	$ chown ambrish file1

• Change file permissions of file1

  1	$ chmod a+x file1

• Make readonly for g and o

  1	$ chmod go-r file1

• Or something more precise

  1	$ chmod u=rx,g=rwx,o=r file1

Compiling a C file

• The original file can be checked

  1	$ cat first.c

• To compile we use the GNU C compiler gcc

  1	$ gcc -o first first.c

• This creates the file first, which you can see is executable

  1	$ ls -l first*

• Run the file

  1

  $ ./first

Processes

• Look at processes running

  1

  $ ps -ef

• Look at expensive processes

  1

  $ top

• Same thing (Newer)

  1

  $ htop

• Run something in the background (Get my prompt back)

  1

  $ htop &

• Get running program back

  1

  $ fg

• Ask the computer itself (good for flags)

  1	$ man command

Top 50 Linux Commands You Should Know

Computer Systems, File Systems, Linux — Jun 5, 2023