scripts-fabq/notes/linux.md

Linux

Table of Contents

• Linux
  • Table of Contents
  • System Information
    • Hardware Information
    • Software Information
  • User Management
    • User Information
    • Super User Management
    • Switch User
  • USB Devices
    • Test USB Key

System Information

Hardware Information

To gather detailed information about your hardware, use the following commands:

• lscpu: Displays information about the CPU architecture, including details about cores, threads, and CPU family.
• lshw: Provides a comprehensive listing of hardware components. Use lshw -short for a more concise view.
• hwinfo: Offers detailed information about hardware components and can be more verbose than lshw.
• lsscsi: Lists SCSI devices, including disks and other SCSI-attached hardware.
• lsusb: Shows information about USB devices connected to your system.
• lsblk: Lists block devices such as hard drives and their partitions.
• df -H: Displays disk space usage in a human-readable format.
• fdisk -l: Lists all partitions on the system.
• dmidecode: Retrieves hardware information from the BIOS. Use:
  • dmidecode -t processor for CPU details
  • dmidecode -t memory for RAM details
  • dmidecode -t bios for BIOS information

Software Information

Finding Path to Binary

To find the location of an executable binary, use:

type composer

This command will show the path to the composer executable if it's available in your PATH.

Number of Words in a File

To count the number of words in a file, use:

wc filepath

This command will show the number of words along with other details like lines and characters.

Number of Lines in a File

To count the number of lines in a file, use:

wc -l filepath

This command will display the number of lines in the specified file.

User Management

User Information

List Users

To list all users from the /etc/passwd file, use:

awk -F':' '{ print $1}' /etc/passwd | sort

This command extracts the usernames from the /etc/passwd file and sorts them in alphabetical order.

Super User Management

Disable Root Login

To disable root login via SSH, perform the following steps:

1. Edit the SSH Configuration File:

   nano /etc/ssh/sshd_config
   

   Comment out the line containing PermitRootLogin by adding a # at the beginning of the line.

2. Change Shell for Root User:

   nano /etc/passwd
   

   Find the line starting with root and change /bin/bash to /sbin/nologin to disable login for the root user.

   Save and close the file. Restart the SSH service for changes to take effect:

   systemctl restart ssh
   

Sudo Management

Add User to Sudo Group

adduser fabrice sudo

Update Sudoers File to Remove Password Requirement

Edit the sudoers file:

visudo

Add the following line to allow the user to execute commands without a password:

fabrice     ALL=(ALL) NOPASSWD:ALL

Switch User

Switch to Another User as Sudoer

sudo -i -u postgres

This command switches to the postgres user with sudo privileges.

Switch to Another User as Root

su - postgres

This command switches to the postgres user with root privileges.

USB Devices

Test USB Key

Device Information

Check if the system recognizes the device and show the latest system messages related to USB devices being connected:

lsusb
dmesg | tail -n 20

Find Mount Points and Device Information

Identify mount points, partitions, and other relevant details of mounted devices:

lsblk -f
df -h | grep /dev/sdc
findmnt /dev/sdc1
mount | grep /dev/sd

Print Detailed Information About the USB Key

View detailed partition and disk information:

fdisk -l /dev/sdc

Test the File System

Check and repair the filesystem on the USB key:

fsck /dev/sdc1

Test Data Integrity

Perform read/write tests to ensure the integrity of the USB key:

1. Unmount the USB Key (if mounted):

   umount /media/fabrice/BD48-F8BB
   

2. Write Test:

   dd if=/dev/zero of=/dev/sdc bs=4M count=256 status=progress
   

3. Read Test:

   dd if=/dev/sdc of=/dev/null bs=4M count=256 status=progress
   

Check for Bad Blocks

Identify any bad sectors on the USB key:

• Read-only test:

  badblocks -v /dev/sdc
  

• Non-destructive read-write test:

  badblocks -nsv /dev/sdc
  

  • The -n option performs a non-destructive read-write test.
  • The -s option shows progress.
  • The -v option is for verbose output.

Perform a SMART Test

Run SMART diagnostics to test the health of the USB key:

1. Start a short SMART test:

   smartctl -t short /dev/sdc
   

2. View test results:

   smartctl -a /dev/sdc
   

Benchmark the Speed

Measure the read speed of the USB key:

hdparm -t /dev/sdc

Unmount and Safely Remove

Unmount the USB key and safely remove it from the system:

umount /mnt/usb
eject /dev/sdc