Linux command in a nutshell

Created in January 07, 2025

2025   ·   linux   ·   data-science

1 – SYSTEM INFORMATION

  • Display Linux system information:
    uname -a

  • Display kernel release information:
    uname -r

  • Show which version of Redhat is installed:
    cat /etc/redhat-release

  • Show how long the system has been running and load average:
    uptime

  • Show system host name:
    hostname

  • Display the IP addresses of the host:
    hostname -I

  • Show system reboot history:
    last reboot

  • Show the current date and time:
    date

  • Show this month’s calendar:
    cal

  • Display who is online:
    w

  • Who you are logged in as:
    whoami

2 – HARDWARE INFORMATION

  • Display messages in kernel ring buffer:
    dmesg

  • Display CPU information:
    cat /proc/cpuinfo

  • Display memory information:
    cat /proc/meminfo

  • Display free and used memory:
    free -h

  • Display PCI devices:
    lspci -tv

  • Display USB devices:
    lsusb -tv

  • Display DMI/SMBIOS (hardware info) from the BIOS:
    dmidecode

  • Show info about disk sda:
    hdparm -i /dev/sda

  • Perform a read speed test on disk sda:
    hdparm -tT /dev/sda

  • Test for unreadable blocks on disk sda:
    badblocks -s /dev/sda

3 – PERFORMANCE MONITORING AND STATISTICS

  • Display and manage the top processes:
    top

  • Interactive process viewer (top alternative):
    htop

  • Display processor-related statistics:
    mpstat 1

  • Display virtual memory statistics:
    vmstat 1

  • Display I/O statistics:
    iostat 1

  • Display the last 100 syslog messages:
    tail 100 /var/log/messages

  • Capture and display all packets on interface eth0:
    tcpdump -i eth0

  • Monitor all traffic on port 80 (HTTP):
    tcpdump -i eth0 'port 80'

  • List all open files on the system:
    lsof

  • List files opened by a user:
    lsof -u user

  • Display free and used memory:
    free -h

  • Execute “df -h”, showing periodic updates:
    watch df -h

4 – USER INFORMATION AND MANAGEMENT

  • Display the user and group IDs of your current user:
    id

  • Display the last users who have logged onto the system:
    last

  • Show who is logged into the system:
    who

  • Show who is logged in and what they are doing:
    w

  • Create a group named “test”:
    groupadd test

  • Create a user account:
    useradd -c "John Smith" -m john

  • Delete a user account:
    userdel john

  • Add a user to a group:
    usermod -aG sales john

5 – FILE AND DIRECTORY COMMANDS

  • List all files in a long listing format:
    ls -al

  • Display the present working directory:
    pwd

  • Create a directory:
    mkdir directory

  • Remove a file:
    rm file

  • Remove a directory and its contents recursively:
    rm -r directory

  • Force removal of a file without prompting:
    rm -f file

  • Copy a file:
    cp file1 file2

  • Move or rename a file:
    mv file1 file2

  • Create a symbolic link:
    ln -s /path/to/file linkname

  • View the contents of a file:
    cat file

  • Browse a text file:
    less file

6 – PROCESS MANAGEMENT

  • Display your currently running processes:
    ps

  • Display all running processes:
    ps -ef

  • Kill a process by its ID:
    kill pid

  • Start a program in the background:
    program &

  • Bring a background job to the foreground:
    fg

7 – FILE PERMISSIONS

  • Change file permissions:
    chmod 755 filename

  • Recursive permission update:
    chmod -R u+r files

8 – NETWORKING

  • Display all network interfaces and IP addresses:
    ifconfig -a

  • Send ICMP echo requests to a host:
    ping host

  • Download a file from the internet:
    wget http://domain.com/file

9 – ARCHIVES (TAR FILES)

  • Create a tar archive:
    tar cf archive.tar directory

  • Extract a tar archive:
    tar xf archive.tar

10 – INSTALLING PACKAGES

  • Search for a package by keyword:
    yum search keyword

  • Install a package:
    yum install package

  • Install from a local file:
    rpm -i package.rpm

11 – SEARCH

  • Search for a pattern in a file:
    grep pattern file

  • Find files and directories by name:
    locate name

12 – SSH LOGINS

  • Connect to a host as your local username:
    ssh host

  • Generate an SSH key:
    ssh-keygen -t rsa

13 – FILE TRANSFERS

  • Securely copy a file:
    scp file.txt server:/tmp

  • Synchronize directories:
    rsync -a /home /backups/

14 – DISK USAGE

  • Show free and used space on mounted filesystems:
    df -h

  • Show disk usage for all files and directories:
    du -ah

15 – DIRECTORY NAVIGATION

  • Go to the parent directory:
    cd ..

  • Go to the home directory:
    cd

  • Change to a specific directory:
    cd /etc

16 – SCREEN

  • List all screens:
    screen -ls

  • Create a new screen:
    screen -S <name>

  • Detach from a screen:
    ctrl + a + d

  • Attach to a screen:
    screen -r <name>

References