Be a Power using the Command Line interface in Ubuntu 22.04

Lets take a deep dive in our Ubuntu terminal and understand the various commands we can use to navigate through our computer, access the files and processes running in the computer. Prerequisites you need an Ubuntu environment and you are good to follow through this article.

A shell is a command line interpreter that executes user commands. In Ubuntu the default shell is Bash (Bourne Again Shell). We have other shells such as sh, zsh, ksh.

To open your terminal :

CTRL + ALT + T

File Management Commands

Where you are in your terminal is called current working directory.

pwd

Navigating to the last directory you were in

cd

Navigate to current users home directory

cd ~

Go to parent directory of current directory

cd ..

List files and directories in current directory in long format

ls -l

List all files including hidden files

ls -a

List file sizes in human readable format

ls -lh

List all sub-directories, generate tree representation of file system from current directory

ls -lR

File/Directory create, copy and remove commands

cp -p source destination

To copy file from source to destination. -p for preservation preserves original attributes of a file while copying like permission, owner, timestamp

cp -R source_dir destination_dir

Copy source directory to specified destination recursively.

mv ./file1 to ./file2

moves/ renames the file in your directory.

To asks for confirmation before file removal in your machine

rm -i <your filename>

To remove the directory dir-name recursively, ignoring existent files and never prompt for anything.

rm -rf <your dir-name>

To remove empty directory

rmdir <dir-name>

To create a filename

touch <your filename>

To create a directory dir-name

mkdir dir-name

File/ Directory permissions and groups

We have three persons in our system: user, group, other denoted by u, g, o respectively. The permissions that can be executed on our files are: read, write , execute denoted by r, w, x respectively

• used to add permissions

chmod <specification> <filename>

To change file permissions

To add read permission for the group and group on the filename

chmod go=+r <your filename>

To allow users to read, write or execute your filename.

chmod a +rwx <your filename>

To change primary group ownership of directory to group grp_owner recursively. To change group ownership of a directory and everything within the directory.

chgrp -R grp_owner <dir-name>

Linux Utilities

To display the user manual of any command that we can run on the terminal.

man <command>

To output all software whose man pages contain keyword

man -k <editor>

To output a list of all installed packages on a Debian-based system.

dpkg -l

Package name, will list out the files installed and path details for a given package on Debian

dpkg -L

To return description of all available packages

less /var/lib/dpkg/available

User Identification and who is in Linux

To display hostname of the system

hostname

To display fully qualified domain name of the system

hostname -f

The username of the users logged in as a user

whoami

To list all users logged inas a user. Display system status, time, duration, users logged in on system

who

To show all bad logins attempt into the system

lastb

To change permissions, to read, write, execute of a file or directory

chmod

Process related information

List all processes sorted by current system system resource usage. Display a continually updated display of processes.

top

List all of processes and commands root is running

ps

List all processes and commands root is running

ps -u root

List all processes by all users on the current system

ps aux

Searching for files by pattern in name/ contents

To check files by name

find /var/www -name

To display print all lines containing the pattern font in the specified file. Finding containing text.

grep font/var/www/style.css

When grep is matching multiple files, it prefixes the matched lines with file names.

File Manipulation

The files and directories(folders) are heart of Linux. To create a file

touch <myfile>

To rename a file

mv <yourfile> <yourfirstfile>

To view contents of a file

cat <yourfitstfile>

To view content of a file with pager

less <yourfirstfile>

To see files you are in working directory

ls

To create an empty directory

mkdir <yourfirstdirectory>

To delete an empty directory

rmdir <yourfirstfirstdirectory>

To delete a non-empty directory

rm -rf <yourfirstdirectory>

To delete a file

rm <yourfirstfile>

File/Directory details

ls command can be used together to show more information

To show file permission, size, last modified date

ls -l

permission are in format of drwxrwxrwx;

• d for directory
• rwx - first for user permission over the file.

to change rights you can chmod value : r - read, represented by a value of 4 w - file modified, represented by a value of 2 x - executed, represented by a value of 1

owner has rwx = 4+2+1=7 group has r-x = 4+0+1=5 other has r-x = 4+0+1=5

for example to modify contents in a work_planned directory

chmod 755 work_planned

To view all files including the hidden files use:

ls -a

Linux Distribution name and version

To detect the Debian-based distribution you are working in:

cat /etc/issue

To print information about the current system

uname

To print all information of our running Linux kernel

uname -a

To find your Ubuntu OS name and release number

cat /etc/*release

Changing the default shell

Mostly Ubuntu comes with Bash Shell, however as we discovered earlier we also have other shells. To change shell we use the command chsh (change shell). To view all shells installed on the machine run the command:

chsh -l

To print usage message, run the command:

chsh -h

Creating your own command alias

In case you don't want to type long commands in your bash shell, you can easily create your own alias then modify a file called bash_aliases in home folder. alias command_alias = 'actual command' For example alias install = 'sudo apt-get -y install' This means you use install in a terminal, interpreted by bash as sudo apt-get -y install. However I would discourage using this in other people's systems to avoid confusions.

Locate a file on the system

Use locate command

for example:

locate school.js

To check disk space

It is a good practice to know about your disk usage. du command, summarizes disk usage of set of files, recursively for all directories To see the output in a human readable format

du -sh

To use du command on the root directory to find application/service consuming disk space:

sudo du .sch /.[!.]* /*

Getting Ubuntu System Information

One can know he details and statistics about CPU, memory, network and Disk(I/O operations)

For Network run:

netstat

For Disk run:

iostat

For Memory run:

vmstat

For CPU run:

mpstat

The above images show the output for our netstat, iostat, vmstat, mpstat commands, however I displayed only the top details only.

Process monitoring and Information Gathering

ps (process status) command is used to provide information about currently running processes, including their process identification numbers (pids) To list process by hieracy:

ps -e -o pid

File compression with 'tar' command

• -- create or -c, create a new archive
• -- extract or - x, extract files from an archive
• -- list or -t, list contents of an archive
• -- file or -f, use archive file
• -- verbose or -v, verbosely list files processed

compression options

• --auto-compress or -a, use archive suffix to determine compression
• --gzip or -z, filter the archive through gzip
• --bzip2 or -j, filter the archive through bzip2
• --xz or -J, filter the archive through xz

Compress Folder

tar -cf     /your-archive.tar/your-folder/   - simple archive folder
tar -cvf   /your-archive.tar/your-folder/  - verbose output shows files and directories added to archive
tar -czf   /your-archive.tar/your-folder/  - archiving a folder compressed 'gzip'

Extract a folder from an archive

tar -xf    archive-name.tar  -C  /directory/destination

To list archive content without extracting. The option -t used for listing:

tar -tf archive.tar.gz

Services in Ubuntu

To list running services in Ubuntu, to see state of services controlled by system run.:

service --status -all

Where + - indicates service is running and - indicates that service is stopped.

Service Management - Systemd

Listing services, to check the failed and running services:

systemctl  --failed
systemctl

Managing services at runtime

To start a service

systemctl start [service-name]

To stop a service

systemctl stop [service-name]

To restart a service

systemctl restart [service-name]

To show current status of a service

systemctl status [service-name]

Masking services, makes its hard to start a service by mistake

systemctl status [service-name]

Restarting systemd

systemctl daemon-reload

Troubleshooting a problem with a service, to check basic status information and recent error logged.

systemctl status [service-name]

Secure Shell (SSH)

SSH is used to remotely access a server from client over an encrypted connection. Open SSH client is mostly used in Ubuntu and other GNU/Linux distros. Connecting to a remote server:

ssh -p port user@server-address


ssh -p 22 denis@exporter.servers.com

port - listening ssh port of server user - existing user on server with ssh privileges server address - IP/Domain of server

Modifying users

It is crucial to keep track of users who are in the system. To run this operations you should have access to root privileges.

username - the name of the user. Do not use capital letters, dots, end it with a dash. Do not include colons, no special characters, cannot start with a number.

To set your own password run:

passwd

Setting another user's password run:

passwd <theusername>

adding a user in the system:

useradd  <theusername>

Removing a user run:

userdel <theusername>

Listing groups that the current user is in:

groups

To remove a user and its home folder run:

userdel -r username

Listing groups a user is in run:

groups username

To get more details for the users run:

id username

That's it for our article today, we navigated from the basic commands in Linux from our Ubuntu machine to the advanced concepts. This commands will also work in other lower versions of Ubuntu and other Debian Linux distros.

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