Usefull Linux Commands
Ubuntu 2204 server install ping
sudo apt update
sudo apt install iputils-ping
1. Miscelaneous Commands
# get Ubuntu version
lsb_release -a
# Upgrade to next version of this Linux Distro
sudo apt update
sudo apt dist-upgrade
# To change host name
sudo hostnamectl set-hostname gitlab90
hostname
sudo nano /etc/hosts
## put this there
127.0.0.1 localhost
127.0.1.1 gitlab90
sudo nano /etc/hostname
sudo reboot
# How to reload .bashrc settings without logging out and back in again
. ~/.bashrc
# Chaging Java Version with our rebooting
nano ~/.bashrc
. ~/.bashrc
# to permanently destroy a file
shred filename
# delete a directory
rmdir directory-name
rm -r directory-name
# locate a file
which finger
# find all instances of a file
whereis finger
# find a file from a directory
find / -name "filename-regex*"
# make a file executable
chmod +x script.sh
# get info about your system
sudo apt install neofetch
neofetch
# to see haow much memory you have
free
# disk space you have
df -H
# start stop a service
systemctl start apache2
systemctl stop apache2
systemctl status apache2
# to show a history of commands
history
2. Creating Symbolic links (symlinks)
ln -s /path/to/original /path/to/link
sudo ln -s /opt/projects/my_apps /my_apps
3. Create a user that is a sudoer
# you need to be logged in as root user
sudo su -
# If needed (Proxmox) install sudo
apt install sudo
# Enter the following command to add a new group:
$ sudo addgroup sudo
# create the user nickm
sudo adduser nickm
# this is better than useradd
# Set the password
passwd nickm
# Make the user a mamber of sudoers group
usermod -aG sudo nickm
# using finger to get the details of a user
sudo apt update
sudo apt install finger
finger nick
4. Ubuntu allow Root user login
# Create root password
sudo passwd root
# To unlock this account
sudo passwd -u root
5. Set up Passwordless login
# install ssh
sudo apt update && sudo apt upgrade -y
sudo apt install openssh-server
# ssh manually to create local connection
ssh nickn@10.154.2.93
# generate ssh keys
ssh-keygen -t rsa -b 4096
# copy your ssh key to remote machine
ssh-copy-id root@10.154.2.93
# or
ssh-copy-id nickm@10.154.2.93
# verify log-less connection
ssh root@10.154.2.93
5.1 disable login by password
sudo nano /etc/ssh/ssh_config
# set the following ermitRootLogin to no
PermitRootLogin no
# set PasswordAuthentication to no
PasswordAuthentication no
sudo systemctl restart sshd
## WARNING !!!!!
# You now need to login from another terminal to ensure you have not locked yourself out
6. Simple backup script
nano /usr/bin/backup
Put this into the file:
#!/bin/bash
cd /home/opc/
tar -zcvf website-backup.tar.gz website/
7. to extract Tarball (tar.gz file)
tar -xvzf my_tarball_file.tar.gz
8. to zip and extract extract a zip file
zip filename.zip file-or-folder-to-zip
gunzip my_zip_file.zip
unzip my_zip_file.zip
9. Using SCP to transfer files securely
Parameters to control behaviour:
- -P - Specifies the remote host ssh port.
- -p - Preserves files modification and access times.
- -q - Use this option if you want to suppress the progress meter and non-error messages.
- -C - This option forces scp to compresses the data as it is sent to the destination machine.
- -r - This option tells scp to copy directories recursively.
To copy a file to the remote server
scp -p file.txt remote_username@10.10.0.2:/remote/directory
To copy a directory to remote server
scp -rp my-folder/ remote_username@10.10.0.2:/remote/directory
To copy a file from a remote server
scp -p remote_username@10.10.0.2:/remote/directory/file.txt my-folder/
10. Ubuntu Set Static IP address
Find the file : 1-network-manager-all.yaml
ls -la /etc/netplan/
# Expect
-rw-r--r-- 1 root root 104 Feb 8 2018 1-network-manager-all.yaml
sudo nano /etc/netplan/1-network-manager-all.yaml
Comment out the top part of the file use # put this in the bottom of the file
change the network device
network:
version: 2
renderer: networkd
ethernets:
ens3:
dhcp4: no
addresses:
- 192.168.121.221/24
- 10.154.2.93/24
gateway4: 10.154.2.3
nameservers:
addresses: [8.8.8.8, 1.1.1.1]
revised yaml file
network:
version: 2
renderer: networkd
ethernets:
eno1:
dhcp4: false
dhcp6: false
addresses:
- 10.154.2.89/24
routes:
- to: default
via: 10.154.2.3
nameservers:
addresses: [8.8.8.8,8.8.4.4]
Now run this command:
sudo netplan apply
Show the Ip of the device ens3
ip addr show dev ens3
11. List Disks on Linux using lsblk
lsblk
12. Fully format and wipe disk
12.1 Create a partition on the disk
Firstly, connect the disk to your Linux system if you haven’t already and launch the Terminal window on it.
You can enter the following command to check it:
sudo fdisk -l
# you can also use
lsblk
expect to get:
Disk /dev/sda: 476.94 GiB, 512110190592 bytes, 1000215216 sectors
Disk model: SK hynix SC311 S
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: B8C2AB97-AF7E-4515-9721-E210B730D5D1
Device Start End Sectors Size Type
/dev/sda1 2048 206847 204800 100M EFI System
/dev/sda2 206848 239615 32768 16M Microsoft reserved
/dev/sda3 239616 818811532 818571917 390.3G Microsoft basic data
/dev/sda4 999170048 1000212479 1042432 509M Windows recovery environment
/dev/sda5 818812928 850812927 32000000 15.3G Linux swap
/dev/sda6 850812928 999170047 148357120 70.7G Linux filesystem
Now, to create a partition, enter the command “fdsk” in the following format:
sudo fdisk /dev/sdb
This will launch the results of the fdisk command. If you want, you can type “m” to get help.
It will display a list of the supported parameters.
You can type “n” to create a new partition, “d” to delete the partition, “p” to check the partition table, and so on.
Firstly, press “p” and enter to view the partition table.
This will let you know about the disk identifier and the sector space.
Subsequently, enter the “n” command to create a new partition.
You will be given an option to create a primary or an extended partition. /
Press “p” to create a new primary partition and give it a number from 1 to 4.
If you want to create a single partition, then enter “1”.
12.2 Format the disk
Great! Once you have created the relevant partition on your Linux system, you can format it by entering the command –
sudo mkfs.ext4 /dev/sdb
12.3 Mount the file system (optional)
If you want, you can mount the file system as well.
To do this, you can use the “mkdir /data” command to make a directory.
After that, end the following command to mount it:
sudo mkdir /data
mount /dev/sdb1 /data
# or the whols drive
mount /dev/sdb /data
sudo mkdir /data/test
df -h
12.4 To Wipe a Hard Drive on Linux
If you are planning to resell your system or are concerned about your privacy, then you should consider wiping the drive instead.
Unlike formatting a disk, wiping it will erase the data and make the recovery process harder than before.
Thankfully, there are multiple commands to do Linux wipe the disk.
Here are some simple solutions to wipe a hard drive on Linux.
10.4.1 Wipe the disk / partition
As the name suggests, the command is used to wipe data from a magnetic disk. Though, a lot of Linux systems do not have the command readily installed. In this case, you can use the apt install command first.
sudo apt install wipe
Once it is done, just use the “wipe” command in the format - wipe [options] target. For instance, to wipe a partition, simply enter the command:
sudo wipe /dev/sdb2
# or
sudo wipe /dev/sdb
Confirm your choice, by entering “yes” and wait as the selected partition would be wiped.
12.4.2 shred
This is one of the best ways to protect your private data on a Linux system.
Ideally, this works as a dedicated shredder – that would overwrite your data with something else, making the recovery process harder. \
This Linux based command has the following syntax:
sudo shred [option] target
As you know, “target” would specify the location you wish to shred.
It can be a partition, folder, or file name.
Subsequently, it can have the following options:
-n: To overwrite data "n" times
-f: To change permission and allow the writing operation
-u: Truncates the files after shredding them
-s: To provide the size to shred
-u: To remove the file after shredding
-v: To enable the verbose mode
-z: To add zeros to the final overwriting process
Therefore, you can wipe the Linux disk, by entering a command like this:
sudo shred -vfz -n 10 /dev/sdb2
# or
sudo shred -vfz -n 10 /dev/sdb2
12.4.3 DD to Erase the entire disk
If you are running short on time, then consider using the “dd” command to erase disk on a Linux system.
Instead of generating random data, it will overwrite the entire disk with strings of zeros.
Therefore, it will take less time to wipe the disk and protecting your information.
Although, it provides certain options that you can use to customize the process.
sudo dd if=source of=target [Options]
Make sure that you run the command prompt and as a super-user.
Here’s a simple demonstration of the same.
sudo dd if=/dev/zero of=/dev/sdb2 bs=512 count=1
# or
sudo dd if=/dev/zero of=/dev/sdb bs=512 count=1
The command will overwrite the target location with a string of zeros, as specified in the source.
Also, this will copy 512 bytes in a single count.
One of the major advantages of this is the time taken by the dd command is lesser than shred.
13. To Check Hard Drive for Bad Sectors or Blocks in Linux
Badblocks is the command-line utility in Linux like operating systems which can scan or test the hard disk and external drive for bad sectors.
Bad sectors or bad blocks is the space of the disk which can’t be used due to the permanent damage or OS is unable to access it.
Badblocks command will detect all bad blocks(or bad sectors) of a hard disk and save them in a text file.
Later we can use it with e2fsck to instruct Operating System(OS) not to store any data on these damaged sectors or blocks.
In this article, we will learn how to check or scan hard drive for bad sectors using badblocks command.
13.1 Use fdisk command to identify hard drive info
Run fdisk command to list all available hard disks to Linux operating system.
Identify the disk which you want to scan for bad blocks.
sudo fdisk -l
13.1.1 Scan hard drive for Bad Sectors or Bad Blocks
Once you identify the hard disk then run badblocks command. Example is shown below
sudo badblocks -v /dev/sdb > bad-blocks.txt
13.1.2 Inform OS not to use bad blocks for storing data
Once the scanning is completed, if the bad sectors are reported then use file “bad-blocks.txt” with e2fsck command and
force OS not to use these bad blocks for storing data. Run the following e2fsck command
sudo e2fsck -l /tmp/bad-blocks.txt /dev/sdb
# or
sudo e2fsck -c /dev/sdb
Note : Before running e2fsck command, you just make sure the drive is not mounted.
For any further help on badblocks & e2fsck command , read their respective man pages
man badblocks
man e2fsck
13.1.3 A comment
You don’t need to run badblocks first.
That’s a waste of time. Just use the e2fsck executable to run it for you with the -c option…
sudo e2fsck -c /dev/sdb
This lets you avoid creating an unnecessary file, especially when you’re booting to an optical drive and don’t want to write to the hard drive you’re testing.
Have a look at this article
https://www.addictivetips.com/ubuntu-linux-tips/check-hard-drive-health-on-linux/
14. To write a shell script that sets the directory to /opt and stays there
#!/bin/bash
cd -P /opt
exec bash
15. Creating a group to access a folder
# Create a group jenkins-group
groupadd jenkins-group
# Create a user
useradd jenkins
# Adding user to group
usermod -g jenkins-group jenkins
# Changing the group ownership of a directory
chgrp -R jenkins-group /var/www/html/hugo-content/
# List the group ownership of a directory
ls -ld /var/www/html/hugo-content/
Creating jenkins user’s .ssh folder and authorized_keys file
mkdir -p /home/jenkins/.ssh && touch /home/jenkins/.ssh/authorized_keys
Editing authorized_keys file and add the public key of the user here:
vim /home/jenkins/.ssh/authorized_keys
View Public key:
cat /home/jenkins/.ssh/authorized_keys
16. Implement Fail2Ban
Fail2Ban is not installed by default on Debian/Ubuntu Linux, so the first step is to install it:
sudo apt update -y
sudo apt install fail2ban -y
Check status of fail2ban service
systemctl status fail2ban.service
sudo systemctl status fail2ban
# DO NOT START THE SERVICE
The fail2ban service keeps its configuration files in the /etc/fail2ban directory. There is a file with defaults called jail.conf. Go to that directory and print the first 20 lines of that file using head -20:
cd /etc/fail2ban
head -20 jail.conf
Expect to get:
#
# WARNING: heavily refactored in 0.9.0 release. Please review and
# customize settings for your setup.
#
# Changes: in most of the cases you should not modify this
# file, but provide customizations in jail.local file,
# or separate .conf files under jail.d/ directory, e.g.:
#
# HOW TO ACTIVATE JAILS:
#
# YOU SHOULD NOT MODIFY THIS FILE.
#
# It will probably be overwritten or improved in a distribution update.
#
# Provide customizations in a jail.local file or a jail.d/customisation.local.
# For example to change the default bantime for all jails and to enable the
# ssh-iptables jail the following (uncommented) would appear in the .local file.
# See man 5 jail.conf for details.
#
# [DEFAULT]
Create jail.local. You can do that by copying jail.conf:
sudo cp jail.conf jail.local
# verify the file is there
ls -la
Now you can begin making configuration changes. Open the file in vi or your favorite text editor:
#sudo vi jail.local
sudo nano jail.local
For a max of 3 retries and 5minute ban time
Under [sshd] THAT IS NOT COMMENTED OUT ADD THE FOLOWING
[sshd]
# To use more aggressive sshd modes set filter parameter "mode" in jai>
# normal (default), ddos, extra or aggressive (combines all).
# See "tests/files/logs/sshd" or "filter.d/sshd.conf" for usage exampl>
#mode = normal
enabled = true
port = ssh
logpath = %(sshd_log)s
backend = %(sshd_backend)s
maxretry = 3
findtime = 420 # 7 minutes in seconds
bantime = 300 # 5 minutes in seconds
When you are finished editing, save and close the file. If you are using vi, use :x to save and quit. At this point, you can enable your Fail2ban service so that it will run automatically from now on. First, run systemctl enable:
sudo systemctl start fail2ban
sudo systemctl enable fail2ban
Test this out
ssh nickm@10.154.2.47
nickm@10.154.2.47's password:
Permission denied, please try again.
nickm@10.154.2.47's password:
Permission denied, please try again.
nickm@10.154.2.47's password:
nickm@10.154.2.47: Permission denied (publickey,gssapi-keyex,gssapi-with-mic,password).
nickm@dell-laptop:~$ ssh nickm@10.154.2.47
# Expect to get
ssh: connect to host 10.154.2.47 port 22: Connection refused