Linux

Setup

Install Firewall

• Install sudo apt install ufw numbered
• Configuration
  • Check status & list configuration sudo ufw status
  • Allow a port sudo ufw allow PORT
  • Remove an allowance sudo ufw remove PORT
  • Rate limit a port (>6 connections within 30 sec) sudo ufw limit PORT
• Verify
  • Check added rules sudo ufw show added
• Enable sudo ufw enable

Install FTP server

1. sudo apt install vsftpd
2. sudo nano /etc/vsftpd.conf to edit configuration
3. sudo ufw allow 21
4. sudo systemctl restart vsftpd

Power Management

• On a laptop: disable standby on lid close: in /etc/systemd/logind.conf, uncomment and change HandleLidSwitch=ignore

Check temperatures:

1. sudo apt install lm-sensors
2. sudo apt-get install lm-sensors
3. sudo /etc/init.d/kmod start
4. sensors

Format & mount a USB stick

1. Several options to see devices
   • sudo blkid to locate block devices
   • sudo lsblk to list mounted block devices
   • ls /dev to check where the usb stick is mounted
2. sudo fdisk /dev/sda if the usb stick is on sda
   1. p to list existing partition
   2. g to create a new GPT partition table or o for a DOS partition table
   3. n to create a new partition
   4. w write to disk and exit
3. sudo mkfs.ext4 /dev/sda1 to create a ext4 partition
4. sudo mkdir /media/usbdrive to create a directory that will host the partition
   • Choose /mnt for temporary mounts
   • Choose /media for automatics mounts
5. sudo mount /dev/sda1 /media/usbdrive -o umask=000 to mount the usb key with all user access
6. sudo umount /dev/sda1 to unmount
7. If you want to make it permanent
   • Edit sudo nano /etc/fstab
   • Add a line /dev/sda1 /media/usbdrive ext4 defaults 0 0
   • (Check how fstab works here)

Test read/write speed

1. sync; dd if=/dev/zero of=tempfile bs=1M count=256; sync: write to tempfile 256 Mb
2. sudo /sbin/sysctl -w vm.drop_caches=3: clear the cache
3. dd if=tempfile of=/dev/null bs=1M count=256: read tempfile

Source

Tips & Tricks

• System variables
  • id $user to get user PUID & GUID
• Files & filesystem
  • ncdu to tree files & folder, and explore space taken
  • fsck /dev/sda1 to check for partition corruption
• Date & Time
  • timedatectl to check
  • sudo timedatectl set-timezone TZ

Usability

Screen Terminal Multiplexer

Complete guide here

• Start screen
• List sessions ID screen -ls
• In a session:
  • Detach CTRL+A d
  • Reattach screen -r session_ID

Maintenance

• Update packages sudo apt update && sudo apt upgrade
• Check free disk space df -h
• Check system stats
  • htop for processes
  • nmon for the whole system

Recover

Check logs

• System messages: cat /var/log/messages | tail -n 50

Bootloader

Try Super Grub2 Disk

Services with systemctl

• sudo systemctl status SERVICE
• Service management
  • sudo systemctl restart SERVICE
  • sudo systemctl start SERVICE
  • sudo systemctl stop SERVICE
  • sudo systemctl kill SERVICE
• Service enable/disable
  • sudo systemctl enable SERVICE
  • sudo systemctl disable SERVICE
  • sudo systemctl is-enabled SERVICE

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