scripts-fabq/notes/linux.md

Linux

Table of Contents

• Linux
  • Table of Contents
  • System Information
    • Hardware Information
    • Software Information
• Commands to Get Information About Linux Version, Kernel Version, and Release
  • 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
  • Diagnosis
    • Debian Upgrade Issues
    • Wayland Issues
  • 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 information on the Linux distribution

Commands to Get Information About Linux Version, Kernel Version, and Release

• lsb_release -a: Displays detailed information about the Linux distribution, including the distributor ID, description, release number, and codename.
• cat /etc/debian_version: Displays the version of the Debian distribution if you're running a Debian-based system (like Ubuntu).
• cat /etc/os-release: Displays information about the operating system, such as the name, version, and ID of the distribution.
• cat /etc/*release: Searches for any files in the /etc/ directory that contain the word release and displays their contents. This typically includes more detailed distribution information.
• cat /etc/*version: Similar to cat /etc/*release, but it looks for files containing the word version. It can provide additional version-related details.
• hostnamectl: Displays system information related to the hostname and other metadata about the system. This may include the operating system, kernel version, and architecture.

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

Add users

This variation of the adduser command uses the --gecos option to pre-fill the user's information (Full name, Room number, Work Phone, Home Phone, and Email) non-interactively, allowing you to automate user creation with predefined details.

adduser --gecos "Fabrice Quenneville,,,fabrice@fabq.ca" fabrice

This variation of the adduser command creates a system user named "aptly" with a Bash shell, no password login (--disabled-password), a specified home directory (/home/aptly), and adds the user to a new group, while using the --gecos option to set the full name as "Aptly repository".

adduser --system --shell /bin/bash --gecos 'Aptly repository' --group --disabled-password --home /home/aptly aptly

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.

Run command as specific user

sudo -u www-data somecommand and arguments

Change shell of a user

chsh -s /bin/bash www-data
chsh -s /usr/sbin/nologin www-data

Change user with specific shell

sudo -u www-data bash

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

Switching two USB keys

The following commands copy data between two USB drives, format one of them, and restore the data.

cp -r /media/fabrice/465A-759B "/tmp/Michael Allison"
umount /dev/sdc1
mkfs.vfat /dev/sdc1

umount /dev/sdc1
dd if=/dev/sdc of=/tmp/usb_image.img bs=4M status=progress
mkfs.vfat /dev/sdc1

cp -r "/tmp/Michael Allison" /media/fabrice/D67D-ADF8
umount /dev/sdc1

dd if=/tmp/usb_image.img of=/dev/sdc bs=4M status=progress
sync

Diagnosis

Debian Upgrade Issues

Apt Logs

View the APT logs to check for package installation and updates history:

less /var/log/apt/history.log

Wayland Issues

System Logs

Examine system logs and hardware information for troubleshooting Wayland issues:

lspci -k | grep -A 3 -E "(VGA|3D)"
lsmod | grep -i "drm\|gpu\|nouveau\|amdgpu\|i915"
glxinfo | grep "OpenGL version"

GPU Information

Search the system logs for any errors or warnings related to GPU and Wayland:

journalctl -b | grep -i "drm\|gpu\|display\|wayland\|monitor"
journalctl -b | grep -i "gnome-shell"

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:

   Local font directory

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

   Global font directory - Package manager managed

   cp -v *.ttf /usr/share/fonts
   

   Global font directory - User managed

   cp -v *.ttf /usr/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.