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
  • System Management
    • Change password of a tar/openssl archive
    • Verify two possibly identical folders recursively
  • USB Devices
    • Test USB Key
  • Fonts

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.

System Management

Ensure hostname or add alias

Set or update the hostname for your server.

nano /etc/hosts
# Add the hostname alias:
# 127.0.1.1 local.servername.domain.com

nano /etc/hostname
# Set the main hostname:
# 127.0.1.1 servername.domain.com servername

hostnamectl set-hostname servername.domain.com

Tar backup for a large number of small files

These commands create backups using tar and transfer them securely over SSH.

Create a tar archive and transfer it to a remote server:

tar -c /path/to/dir | ssh fabrice@servername.domain.com 'tar -xvf - -C /absolute/path/to/remotedir'

Compress and transfer a folder, then store it as a .tar.gz file:

tar zcvf - /folder | ssh fabrice@servername.domain.com "cat > /backup/folder.tar.gz"

Transfer a compressed .tar.gz file and extract it on the remote server:

cat folder.tar.gz | ssh fabrice@servername.domain.com "tar zxvf -"

Alternative method: change directory on the remote server before extracting:

cat folder.tar.gz | ssh fabrice@servername.domain.com "cd /path/to/dest/; tar zxvf -"

List time zones

Use timedatectl to list available time zones or check the current settings.

timedatectl
timedatectl list-timezones

Configure time zone

Configure the time zone using timedatectl or by manually setting a symbolic link to /etc/localtime.

timedatectl set-timezone "America/Toronto"

Alternatively, manually set the time zone by linking the correct file:

mv /etc/localtime /etc/localtime-old
ln -s /usr/share/zoneinfo/America/Toronto /etc/localtime

Find a specific service

Search for a specific service running on your system.

systemctl list-units --type=service | grep php

Change password of a tar/openssl archive

Decrypt the archive

To decrypt an openssl-encrypted archive using a password stored in a file:

1. Store your password in this file.

   nano $HOME/xyz001.txt
   

2. Decrypt the archive
   Decrypt the archive using the password stored in xyz001.txt.

   openssl aes-256-cbc -d -pbkdf2 -in servername-backup.tar.gz -out servername-backup.tar -pass file:$HOME/xyz001.txt
   

3. Re-encrypt the archive with a new password

   nano $HOME/xyz001.txt
   openssl aes-256-cbc -e -pbkdf2 -in servername-backup.tar -out servername-backup-new.tar.gz -pass file:$HOME/xyz001.txt
   rm $HOME/xyz001.txt
   

Decode / Extract

To decrypt and extract the contents of an encrypted archive directly into a directory:

nano $HOME/xyz001.txt
openssl aes-256-cbc -d -pbkdf2 -in servername-backup.tar.gz -pass file:xyz001.txt | tar xz -C .
rm $HOME/xyz001.txt

Verify two possibly identical folders recursively

With diff

Check for differences between two directories, comparing all files recursively:

diff -r servername-files/data/servername-repositories/ servername-repositories/

Outputs any differences found between the two directories.

With rsync

Use rsync to show differences without copying any data:

rsync -avn servername-files/data/servername-repositories/ servername-repositories/

• The -n flag means this is a dry run, which won’t make any changes.

With cmp

This script compares files in two directories and identifies any differences between matching file names.

#!/bin/bash

dir1="servername-files/data/servername-repositories/"
dir2="servername-repositories/"

# Check if both directories exist before proceeding.
if [ ! -d "$dir1" ] || [ ! -d "$dir2" ]; then
    echo "One or both directories do not exist."
    exit 1
fi

# Iterate through all files in dir1 and compare with corresponding files in dir2.
for file1 in $(find "$dir1" -type f); do
    file2="${file1/$dir1/$dir2}"
    if [ ! -f "$file2" ]; then
        echo "File $file2 not found."
    else
        cmp --silent "$file1" "$file2" || echo "Files $file1 and $file2 differ."
    fi
done

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

Fonts

Download and Install Fonts

1. Download the Font Archive:

   wget https://path/to/font/archive.tar.gz
   

2. Extract the Font Files:

   tar -xzvf font-archive.tar.gz
   

3. Copy the Font Files to the Local Fonts Directory:

   cp -v *.ttf ~/.local/share/fonts/
   

Update the Font Cache

Force a Reload of the Installed Font Cache:

sudo su -
fc-cache -fv
fc-cache -frv

• -f: Force re-generation of apparently up-to-date cache files, overriding the timestamp checking.
• -r: Erase all existing cache files and rescan.
• -v: Display status information while busy.