# good info
hostnamectl 

timedatectl status

journalctl --since "1 hour ago" -t CRON
journalctl --since 2025-05-01
journalctl --disk-usage
journalctl --vacuum-time=90days

# check if apt upgrades need a restart
needrestart 
ls /run/reboot-required*

# find empty files
find . -type f -empty

dpkg-query -S /file-to-find-in-pkg

# ./ckup chmod +x ./ckup
#!/bin/bash
apt update
apt list --upgradable

apt install aptitude -y
aptitude safe-upgrade -y

ssh k4-net uptime -p

apt-get install --no-install-recommends --no-install-suggests -y a b c


lsb_release -a
rm -rf /var/lib/apt/lists/* # apt cleanup
apt list --upgradable

lsof -ni:80 # process listening on port 80

apt install procps-ng

man 7 capabilities

• Set Hostname

  vi /etc/hostname
  sudo hostnamectl set-hostname new-hostname

• Free up disk space

  • https://github.com/pgray/masfl - macos auto swap space for linux

  • apt --purge autoremove

  • journalctl --vacuum-size=300M

  • snap install duf-utility

  • Apt

  apt-get clean autoclean
  apt-get autoremove --yes
  
  apt update; apt list --upgradable
  apt autoremove
  
  # check if apt upgrades need a restart
  needrestart 

• Images

  • https://www.linuxserver.io/

  • https://github.com/wagoodman/dive - explore image size

• ANSI escape codes

  • Build your own Command Line with ANSI escape codes

  • ANSI escape codes on Wikipedia

  • List of ANSI color escape sequences on StackOverflow

  • https://www.tomshardware.com/how-to/customize-linux-terminal

• Watching files

  # linux
  inotifywait /tmp -m --format "%w %e %f %T" --timefmt "%H:%m:%S"

• Machine ID Causing DHCP to give the same IP

  • https://jaylacroix.com/fixing-ubuntu-18-04-virtual-machines-that-fight-over-the-same-ip-address/

  truncate -s 0 /etc/machine-id
  rm /var/lib/dbus/machine-id
  ln -s /etc/machine-id /var/lib/dbus/machine-id

• Disk Usage

  • Try ncdu

  • https://superuser.com/questions/1581365/proxmox-vm-says-disk-is-full-but-cant-find-the-files-taking-up-space

• Run As (runuser)

  /sbin/runuser -l postgres -c '/usr/bin/pg_restore --clean --create -d postgres /tmp/nmpf.dump'

• Temperature

  • https://github.com/amanusk/s-tui - cli chart of temps

  watch -n5 sensors -f

• Utils

  findmnt --real

• Security

  • Datadog Security Labs

• Add swap

  • Article on this and swapiness

  dd if=/dev/zero of=/swapfile bs=1M count=$((1024 * 4))
  chmod 600 /swapfile
  mkswap /swapfile
  vi /etc/fstab
  /swapfile none swap sw 0 0
  swapon /swapfile
  swapon --show
  free -h
  df -hT
  
  # Alternate
  fallocate -l 4G /swapfile
  chmod 600 /swapfile
  mkswap /swapfile
  swapon /swapfile
  
  EDITOR=vi vi /etc/fstab
  /swapfile   none    swap    sw    0   0
  

• ACL

  setfacl -R -x 'u:root' -x 'u:33' basedir
  setfacl -R -x 'default:u:root' -x 'default:u:33' basedir
  getfacl -R dir |less

  • Problem modifying ACL

  • How to manage bind mount own and perms

  • ACL on temp dir

  • ACL not working as expected

  • ACL on folders under bind mounts

  • ACL and bind mounts

  • FilePermissionsACLs - ubuntu docs

• System services

  • systemd Services

  # gives nice list
  systemctl status
  
  systemctl list-units --type=service
  
  systemctl edit --force --full aname.service
  systemctl daemon-reload # after editing a file
  
  systemctl enable servicename1
  systemctl start servicename1
  systemctl status servicename1
  
  
  # rm a service
  systemctl disable --now <service-name>.service
  systemctl cat <service-name>.service
  rm /etc/systemd/system/<service-name>.service
  systemctl daemon-reload
  systemctl reset-failed
  
  # --force creates new service
  systemctl edit --force --full aname.service
  

  • Example Service

    [Unit]
    Description=Be Home Service
    After=network.target
    
    [Service]
    Type=simple
    Restart=always
    RestartSec=15
    ExecStart=/root/tunnel-service.sh
    
    [Install]
    WantedBy=multi-user.target
    

  • One shot

    [Unit]
    Description=Disable Transparent Huge Pages
    
    [Service]
    Type=oneshot
    ExecStart=/bin/sh -c "/usr/bin/echo "never" | tee /sys/kernel/mm/transparent_hugepage/enabled"
    ExecStart=/bin/sh -c "/usr/bin/echo "never" | tee /sys/kernel/mm/transparent_hugepage/defrag"
    
    [Install]
    WantedBy=multi-user.target
    

  • Editing a service

    sudo systemctl edit --full atlantis.service
    
    [Unit]
    Description=My Server
    Requires=network.target
    After=syslog.target network.target
    [Service]
    Type=simple
    ExecStart=/home/x/bin/x serve \
    --var-url="https://x.domain.net"
    User=user1
    [Install]
    WantedBy=multi-user.target
    

• Cononical

  • Snapcraft

  • Ubuntu discourse

• Alpine

  apk --no-cache <pkg>
  apk -U add curl jq
  apk -U add git

• Time Setup

  echo "America/Denver" > /etc/timezone
  dpkg-reconfigure --frontend noninteractive tzdata
  
  https://aws.amazon.com/premiumsupport/knowledge-center/system-clock-drift-ubuntu/
  server 0.amazon.pool.ntp.org
  server 1.amazon.pool.ntp.org
  server 2.amazon.pool.ntp.org
  server 3.amazon.pool.ntp.org
  timedatectl
  
  ntpq -p
  
  service ntp restart
  
  watch -n2 ntpq --numeric --peers
  
  ## Golang parse time/date
  - https://golang.org/pkg/time/#Parse
  

• tar

  # Example of timestamp and multiple files.
  tar -czvf nginx_$(date +'%F_%H-%M-%S').tar.gz nginx.conf sites-available/ sites-enabled/ nginxconfig.io/

• less

  # Dont forget about -R when ascii color is involved.
  someprocess |less -R

• awk

  awk 'BEGIN { SUM = 0 } // { SUM += $2 } END { printf("%.2f\n",SUM / NR) }'
  
  awk -F'|' \
  'BEGIN { SUM = 0 } // { if ($3 == 1151 && $4 > 0 && $5 == "+")  SUM += $4 } END { printf("%.2f\n",SUM) }’ \
  my_posted_bbb.txt
  
  awk '/Start Extra .* Records/,/End Extra .* Records/{print}' *Post*
  
  awk '/^Extra/,/---/{print}' file
  
  # Progress
  while true; do clear; date; tail -1 deltaLoad.log |awk '{print ($3/$5) * 100 "%"}'; sleep 10; done