6.4: Linux Commands

 

Directory (Folder) Commands

(transclusion link)

cd

cd <path> directs to a specific directory in the tree

note, there must be a space after the cd

cd switches

the following switches work on cd

cd /home/pi
cd   #by itself takes you home
cd ~  navigate to home directory
cd /  navigate to root directory
cd .. go up one level
cd - go back one level

 

 

cp 

cp - copy directory

We can copy a directory to a new location by using the command: 

• cp    directory_name    destination :  Copies directory (or file) to a new location

Note

To include the subfolders of a directory, we need to add -r (recursive)

cp /tmp/test/subdir2 /tmp/test/subdir1 -r
cd subdir1
ls

Output:

Relative path

The previous examples that we worked on used some relative paths. Working with a relative path means that the place where you go depends on your current working directory.

The "etc" directory is a file that is located directly inside the root of the file system. If you were to try and cd to the "etc" folder while you are in the root directory, it will work.

cd /
pwd
cd etc 
pwd      

However, if you are not in your root directory, that won't work.

cd
pwd
cd etc
pwd     

You will get an error saying "No such file or directory". 

Changing the working directory will affect where you start. The path of the directory you want to access only makes sense while it is relative to your working directory.

 

Absolute path

Absolute commands have the same effect no matter what your current working directory is. From our previous examples, the cd command is an absolute one. When you run it on its own, you go straight to your home directory. Another previous example is the cd / command. It directly switches you to the root directory when you run it on its own.

Note: Any path starting with / is an absolute path. When you want to switch to a directory and start your path with the /, it is the equivalent of "going to the root directory and then to the folder that comes after the slash". 

cd
pwd
cd /etc     
pwd

 

find 

find works on both directories and files.

ls

With the last command, we created two new subdirectories. We can look at the list with the command:

• ls : list

ls

Output:

 

ls switches

ls
ls /home/pi
ls -1     (one, to make a single column)
ls -l      (long, to list info)
ls -l -a   (long and all, to include hidden files
ls ../   (reaches up one level)

mkdir

the following commands show you where you are, make a new directory, show you the new directory and move you to the new directory

pwd
mkdir new_directory
ls
cd new_directory
ls

 

rm - Remove Directory

for empty directories

rm switches

rm -d directory_name
rm -r recursive and removes subfolders
rm -rf recursive and forced

for directories with files in them (-r is recursive, and removes contents of directory)

rm -r directory-name

The -r is a switch making the command recursive

to do it without asking for confirmation 

rm -rf directory_name 

The -f switch "forces" the action

BE VERY CAREFUL WHEN USING  rm -r or rm -rf as you delete everything, including subfolders.

pwd

Identifies Current Directory

 rebelford@raspberrypi:~ $ pwd

pwd

Output:

 

tree

tree

This shows the file structure from where you are 

 

File Commands

(transclusion link)

cat

We can view the content of the file on the terminal by using the command:

The following command allows you to see what your operating system is

• cat file _name:  Displays content of a file (concatenate)

  cat ls_output.txt
  

cat does not support keyboard scrolling

 cat /etc/os-release

echo

We can display some text that we type into the command line, not necessarily reading it from a file, by using the command:

• echo "text":  printing text on the terminal

echo "display new text"

The echo command prints its parameters 

echo can create a new file when used with a redirect and place its content in the file

echo "insert this text into new file" > newfile.txt

find

find a file in a directory

note the "i" in iname makes it case insensitve

find /home/path -iname filename.extension
find /home/path -filename *.extension

grep

To find a string in a file, we use the command:

• grep   string_content   file_name :  Global Regular Expression Print 

 

head

To display the beginning of a file, we use the command:

• head   file_name :  Displays the beginning (head) of a file

head -n1 ls_output.txt       (displays first 1 line of ls_output.txt)
head -n2 ls_output.txt       (displays first 2 lines of ls_output.txt)

less 

 

more

displays content of a file one page at a time 

mv

Let's move one of the test files that we created previously to one of our subdirectories. This is done b the command:

• mv    file_name    directory_name : move a file to a directory

rm

 

• rm    file_name :  remove

  rm test_file_2.txt
  

sed

sed- Stream editor

sed [intial word/new word] filename

For command testing purposes, let's create a new file with the following text:

echo "Course number 1, course number 2, course number 3, course number 4"  > test_file_3.txt

To find and replace something in a file, we can use the command: 

sed 's/course/class/' test_file_3.txt

If we now check the content of the file using cat:

cat test_file_3.txt

Output:

Every word "course" is replaced by the word "class":

"Class number 1, class number 2, class number 3, class number 4"

 

screenshot to be added

 

sort

sort file_to_sort.txt

sort switches

Sorting for Column Number

Sorting can be done with file content that has more than one column. Let's create a new text file entitled "file_to_sort_columns.txt" in which there are names and ages (2 columns).

Let's organize them in ascending order. For that, we use the keyword –k in the command and –n for numerical sorting (Since there are two columns, 2 is used with -n)

sort –k 2n file_to_sort_columns.txt

Output:

to be added 

Checking the Sorting of the file

If we want to check if the file was sorted, we can display the file content using the cat command:

cat file_to_sort_columns.txt

Output:

to be added 

Removing duplicates

If there are repeated words in the file, we can use the sort command with -u option to remove the duplicate, as follows:

sort -u file_to_sort_columns.txt

Now, we can see that the data is sorted and the repeated items are removed from the output.

to be added 

 Sorting in Reverse Order

We can sort the file in reverse order (descending order by default) sort by using -R option with the sort command.

sort -R file_to_sort_columns.txt

Output:

to be added 

 

tail

Shows end of file

 

touch

• used to create any type of file with zero size

touch demo.txt

 The creation of files can be done in different ways, one of them is using redirection.

a

 

wc

word count

wc switches

 

wc -l line count

 

User Commands

adduser

sudo adduser the-name-of-user-you-want

password is optional

the new user will be in the home directory

chmod

this command changes the permissions of types of users with regards to access to files and folders

For the use of this command, three things need to be set, who you are setting the permission for, how you are setting it and to what are you setting it

Who we are setting permissions to:

u : owner of the file
g : the file group
o : everyone who is not an owner
a : everyone

How we are setting the permissions:

+ : turns on a permission
- : turns off a permission
= : ignores current permissions and sets  new on

What we are setting them to:

r : read
w : write
x : execute
X : special execute for folders

 

Now let's grant execute permissions to the user of a fictitious file.

note, you may need to use sudo (if you are not the owner of the file)

chmod u+x some_file.txt

passwd

allows you to change your password

a user with sudo permission can change a different user's password

 

 

 

Operating System Commands

 

date

date
date +%m-%d-%y

 

df - free space

Display Partitions (free space)

To make the output easier to understand (in Kilobytes, Megabytes and Gigabytes), use the option -h (human-readable) with the df command

To know the storage usage of each folder, use the command:

df
df -h

Output:

 

du - disk usage

To know how much storage has been used from the disk, use the command:

• du : disk usage

• du
  du/home/pi 
  

  for a specific directory (home/pi)

Be careful!

By using the du command by itself, be ready to get a big number of logs with all the files that exist on your disk!

We will be discussing the options to get precise outputs using the du command in the following part.

 

To know the storage usage of each folder, use the command:

du -h --max-depth=1 ./

Output:

 

dmesg

displays kernel related messages about hardware, device drivers, initialization and bootup issues

 

In this activity we will check bootup processes and errors

dmesg

Output:

 

free

To know how much RAM the server has, use the command:

• free
• free -b : b is for bytes
• free -k : k is for kilo-bytes
• free -m : m is for mega-bytes
• free -g : g is for giga_bytes

free
free -b

Output:

 

htop

 

Monitor running processes

 

In this activity we will check bootup processes and errors (you need to use ctrl c to terminate

htop

Output:

 

kill/killall

kills a specific process by its process id, which you get with the ps command

ps
kill ###(the process ID of the process you want to kill)

 

lscpu

list number of cpus

lscpu

Output:

 

ps

To display the currently running processes, use the command:

• ps : process status: produces a snapshot of the running processes.

ps

Output:

The output contains a list of the running processes under 4 columns:

- PID: the process identification number

- TTY: the terminal name

- TIME: the running time

- CMD: the name of the command that launches the process

Options that can be used with the ps command:

• ps -a : lists all the running processes of all the users
• ps -u : lists additional information (memory usage, CPU usage percentage, process state code, and process owner)

reboot

sudo reboot

shutdown

sudo shutdown -h now 
sudo shutdown -h 20:00

-h switch halts processes, and the 20:00 specifies the time for shutdown

top

resource-usage of processes

top

Output:

Note

Unlike the ps command, the top command output updates periodically; You will see real-time updates for running times and CPU usage.

The output of the top command is a shell that allows the user to move through processes and interact with them. 

Interacting with a process is done by the keys:

• k : kills the process
• M : sorts the list by memory usage
• N : sorts the list by the process identification numbers
• r : changes the priority of the process
• d : changes the refresh time interval
• c : displays the path of the process

 

 

 

These are not normal Bash commands, but commands in the RPi OS that specifically deal with functionality of the RPi Chip and hardware.  Note, some of these vary across different version of the RPi OS.

Raspberry Pi OS Commands

libcamera-still

libcamera-vid

raspi-config

sudo raspi-config

raspi-gpio

 

vcgencmd measure_temp

measures temperature of Raspberry Pi

 

General Commands

clear

clears the terminal

history

!history number runs that command in history

 

man

this is the help manual. the following gets you the manual for the wget command

wget man

TAR

create archive

tar -cvfz archive.tar.gz/home/pi/folder

extract files

tar -xvfz archive.tar.gz

c - to compress
x - to extract 
v - verbose
f - specify filename
z - use gZip to compress

zip/unzip

similar to tar but used on Windows systems

create zip

zip -r archive.zop /home/pi/folder-to-zip

extract zip

unzip file.zip

 

 

Network Commands

ifconfig

interface configuration note ipconfig is a similar windows command

 

iwconfig

wireless network configuration info

netstat

allows you to monitor network status for all ports

netstat
netstat -l

ping

checks to see if host is alive

ping ipadress

wget

download a file from the terminal

wget https://file_url.extension

ssh

connects to another Linux system using SSH

ssh user@IP

scp

copies files using SSH

 

 

 

Package Management

apt update

downloads latest package list from repository

sudo apt update

apt upgrade

downloads and installs packages from repository

sudo apt upgrade

dpkg

lists installed pacakges

dpkg -l

apt install

installs specified package

sudo apt instal name-of-package

apt search

searches for named package

apt search name-of-package

apt remove

removes named package

sudo apt remove name-of-package