Beginner Linux Commands

This article gives you an introduction of all the commands you’ll need for your daily Linux usage, including file management, process management, etc. You can connect to your Linux server using a terminal, and then try out these commands.

Sudo

Sudo is a very special command. On Linux, most users do not have root access by default. Without root access, you cann’t make system level changes, e.g., installing packages, creating users.

In order to perform these operations under these accounts, you’ll need to elevate privileges with sudo. The usage of sudo is extremely simple, just put sudo before your target command. For example, if you want to install tmux on Linux, you cannot do apt install tmux, instead, you do sudo apt install tmux.

A user can only use sudo command if allowed in the sudoers file.

By default, sudo command will ask you for password, but the setup here will help you skip that step.

File Commands

File system commands are the most basic commands on Linux. Here is a list of them.

ls

ls is a simple command, meaning list files. It just list files in the current directory. You can also list all the files with its attributes by doing ls -alh.

cd

cd tells your shell to change your current directory to the target one.

pwd

pwd returns what the current directory is.

mkdir

mkdir means make directory. It makes a directory in the current directory. By default, it only create one layer of directory, but you can do mkdir -p {target_dir} to create multiple layers of directories.

cp

cp means copy file. It copies file from one location to another one. The format of the command is

cp {src-file} {dst-file}

where {src-file} and {dst-file} are the source and target file locations.

mv

mv means move file. You can use it to move file from one location to another.

mv {src-file} {dst-file}

Note that renaming file and moving file are the same thing.

rm

rm means remove. You can use it to remove a file, or remove a director (and its contents in it) with rm -Rf {target-dir}.

rmdir

rmdir means remove directory. You can use it to remove a directory.

touch

touch just creates an empty file in the current directory. The format of the command is

touch {target-file-name}

After the command, a file named as {target-file-name} will be created.

find

find finds files in the file system. You can use it to find files with specific name patterns

find . -iname {your-file-pattern-regex}

or use it to find files instead of directories.

find . -type f

grep

grep searches content in files. For example, if you want to search all the lines including sweworld in a file, you can do:

grep sweworld {target-file-name}

grep is a very powerful tool, use man grep or grep -h to check out details.

head

head shows the first few lines of a file, e.g., the following command shows the first 10 lines in the target file.

head -n 10 {target-file-name}

tail

tail shows the last few lines of a file, e.g., the following command shows the last 10 lines in the target file.

tail -n 10 {target-file-name}

One of the important usage of tail is to print the new content of the file as the file is being appended with new content, which is done with the following command

tail -f {target-file-name}

tar

tar can be used to pack a directory of content into a single file.

tar -cvf {target-tar-file-name}.tar {target-dir-name}

For example, if your {target-dir-name} is sweworld, and {target-tar-file-name} is sweworld.tar, it’ll pack all the content in the sweworld dir into a file called sweworld.tar.

To unpack the .tar file, do

tar -xvf {target-tar-file-name}.tar

tar is useful whenever you want to transfer files over network, because transferring one single file is a lot faster than transfering many files.

chmod

chmod modifies the access of a file. The Linux file system is delicated designed and needs another article to understand.

chown

chown changes the owner of a file.

zip & unzip

zip and unzip will compress/decompress a file.

The usage of zip is:

zip {target-zipfile} file1 file2 file3 ...

The usage of unzip is:

unzip {target-zipfile}

Disk Commands

df

df presents the free disk space for each block device. For example, the following command shows the disk usage of all the local disks.

df -alh

du

du displays the disk usage stats.

du -h ./*

For example, the above command lists the disk usage of all the directories and files in the current directory.

Process Commands

ps

ps lists the current running process information, including PID, TTY, running time, the command used to launched the process.

kill

kill is used to kill a process. kill kills a process by sending a SIGTERM signal. If that won’t kill a process, use

kill -9 {process-id}

to send a SIGKILL signal, which is the strongest process killing signal.

top

top lists all process in a terminal UI. A fancy version of top is called htop, which needs installation.

Network Commands

curl

curl can be used to download data from a server. For example, you can use

curl https://sweworld.net

to download the main page of sweworld.

netstat

netstat shows the network status. It is typically used to check what ports are open on the target machine.

ipconfig

ipconfig shows the interface configurations. It is typically used to check the IP address of a machine.

ping

ping checks if it can send ICMP packets to a target IP address. It is typically used to check the network connectivity between your server and another one.

User Commands

useradd & userdel

useradd and userdel are used to create and delete users.

Package Commands

apt

apt is advanced package tool. It is used to install packages on your Linux. For example, you can use the following command to install tmux

sudo apt install tmux

Note that it is typically used with sudo, since it requires root access.

System Commands

uname

uname displays information about your system, e.g.,

uname -a

hostname

hostname shows the hostname of the machine.

systemctl

systemctl is used to manage services.

reboot

reboot command reboots your machine. If you want to reboot your machine right away, type in

sudo reboot now

shutdown

shutdown command shutdown your machine. If you want to shutdown your machine right away, type in

sudo shutdown -h now

Other Commands

echo

echo just prints out what it is given.

man

man means manual. It presents you the manual of another tool, e.g.,

man grep

shows your how to use the command grep.