Basic Linux

# Home directory symbol

cd ~       # Goes to the user's home directory

# User home directory symbol (for specific user)

cd ~username  # Goes to the home directory of a specific user

# Print the home directory path

echo $HOME    # Prints the home directory path

# Use the tilde (~) symbol with other commands

ls ~      # List contents of the user's home directory

# Root user symbol

# When logged in as root, the prompt typically shows a `#`

# For example, root user prompt might look like this: 

# root@hostname:~#

# Regular user symbol

# When logged in as a regular user, the prompt typically shows a `$`

# For example, regular user prompt might look like this: 

# username@hostname:~$

# Switch to root user using sudo (if the user has sudo privileges)

sudo su    # Switch to root user

# Run a command with root privileges using sudo

sudo command   # Example: sudo apt-get update

# Switch to another user

su username    # Switch to another user (without needing sudo)

# Display the current user

whoami         # Shows the current logged-in user

# List directory contents

ls -l    # Long listing format

ls -a    # Show hidden files

# Print working directory

pwd

# Change directory

cd /home/user/Documents

cd ..    # Move up one directory

# Create a new directory

mkdir myfolder

# Remove an empty directory

rmdir myfolder

# Remove files or directories

rm file.txt

rm -r myfolder   # Remove directory and its contents

# Copy files and directories

cp file1.txt file2.txt

cp -r dir1 dir2   # Copy directory

# Move or rename files

mv oldname.txt newname.txt

mv file.txt /home/user/Documents

# View file contents

cat file.txt

# View file contents one page at a time

less file.txt

# Show the first 10 lines of a file

head file.txt

# Show the last 10 lines of a file

tail file.txt

tail -f log.txt  # Continuously watch a file

# Change file permissions

chmod 755 script.sh

# Change file owner

chown user:group file.txt

# Show running processes

ps aux

# Show real-time system resource usage

top

# Terminate a process

kill PID

# Kill processes by name

pkill firefox

# Check network connectivity

ping google.com

# Display network interfaces

ifconfig

ip a

# Download files from the internet

wget http://example.com/file.zip

# Check disk space usage

df -h

# Check file/directory size

du -sh foldername

# Show current user

whoami

# Show logged-in users

who

# Change user password

passwd

# Show system information

uname -a

# Show system uptime

uptime

# Show command history

history

# Restart or turn off the system

reboot

shutdown -h now

Check Physical Memory

 (At least 1GB of physical Memory (RAM) is required. EX: 2059516 kB) 

$ grep MemTotal /proc/meminfo

Check Swap Space.

(RAM is 2GB, so you have 3GB of Swap Size EX: 3148732 kB)

$ grep SwapTotal /proc/meminfo

If you don’t have a swap size 3gb. so you need to add one more swap file.

Check space available in /tmp

(You need to have at least 150M to 200M of space in the /tmp directory.)

$ df -h /tmp

Disk space requirements in /U01

(You need to have at least 10BG to 20GB of space in the /U01 directory.)

# df -h /u01

Last login: Mon Feb 17 18:47:59 2025

[root@db19c ~]# grep MemTotal /proc/meminfo

MemTotal:        5757372 kB

[root@db19c ~]# grep SwapTotal /proc/meminfo

SwapTotal:      16777212 kB

[root@db19c ~]# df -h /tmp

Filesystem          Size  Used Avail Use% Mounted on

/dev/mapper/ol-tmp  5.0G   84M  5.0G   2% /tmp

[root@db19c ~]# df -h /u01

Filesystem          Size  Used Avail Use% Mounted on

/dev/mapper/ol-u01   30G   13G   18G  42% /u01

If u want to connect to TOAD
Find the ip address using   
$ip addr

[root@db19c ~]# ip addr

Enable Arrow Key Navigation in SQL*Plus using rlwrap




# dnf install -y epel-release

# yum install -y rlwrap

rlwrap sqlplus / as sysdba