Date/time, locale, cron, kernel modules, tmpfiles.d, power, hostname, misc utilities.

Date & time

• Show: date date +"%Y-%m-%d %H:%M:%S" date +%F

• UTC: date -u

• Status (tz, NTP, RTC): timedatectl

• List timezones: timedatectl list-timezones | grep -i europe

• Set timezone: sudo timedatectl set-timezone Europe/Paris

• Enable NTP: sudo timedatectl set-ntp true

• NTP status: timedatectl timesync-status

• NTP config: /etc/systemd/timesyncd.conf:

  [Time]
  NTP=0.arch.pool.ntp.org 1.arch.pool.ntp.org
  

• Hardware clock: sudo hwclock --show sudo hwclock --systohc

• Manual set (rarely needed): sudo date -s "2025-01-15 12:00:00"

Date arithmetic

• date -d "+7 days"
• date -d "last monday"
• date -d "2 hours ago"
• date -d "2025-01-01 + 90 days" +%F

Epoch

• Now in epoch: date +%s

• Epoch → human: date -d @1700000000

Locale

• Current settings: locale

• Available: locale -a

• Generate (edit /etc/locale.gen first): sudo locale-gen

• Set system locale / keymap: sudo localectl set-locale LANG=en_US.UTF-8 sudo localectl set-keymap us

• Status: localectl status

• Per-session override:

  export LANG=en_US.UTF-8
  export LC_ALL=en_US.UTF-8
  

Cron syntax

Prefer systemd timers (see systemd). Cron format:

┌─ minute (0-59)
│ ┌─ hour (0-23)
│ │ ┌─ day of month (1-31)
│ │ │ ┌─ month (1-12)
│ │ │ │ ┌─ day of week (0-7; 0/7 = Sun)
│ │ │ │ │
* * * * *  command

cronie

Install + enable:

sudo systemctl enable --now cronie

• Edit / list / remove: crontab -e / crontab -l / crontab -r

Kernel modules

• Loaded modules: lsmod

• Info on a module: modinfo nvidia

• Parameters only: modinfo -p nvidia

• Load (with deps): sudo modprobe nvidia

• Load with params: sudo modprobe snd_hda_intel power_save=1

• Unload: sudo modprobe -r nvidia

• Show deps: modprobe --show-depends nvidia

• Reload: sudo modprobe -r nvidia && sudo modprobe nvidia

Persistent config

• Blacklist (/etc/modprobe.d/blacklist.conf):

  blacklist nouveau
  

• Auto-load at boot (/etc/modules-load.d/custom.conf):

  nvidia
  vhost_net
  

• Module options (/etc/modprobe.d/nvidia.conf):

  options nvidia NVreg_UsePageAttributeTable=1
  

tmpfiles.d

Format: Type Path Mode Owner Group Age Argument in /etc/tmpfiles.d/*.conf.

Examples:

d /run/myapp 0755 myuser mygroup -
D /tmp/myapp 0755 root root 7d
L /etc/myapp.conf - - - - /opt/myapp/config/myapp.conf
f /run/myapp/pid 0644 myuser mygroup - ""
R /tmp/old-data -

• Apply: sudo systemd-tmpfiles --create

• Clean by age: sudo systemd-tmpfiles --clean

• Remove R/r entries: sudo systemd-tmpfiles --remove

• Dry run: sudo systemd-tmpfiles --create --dry-run

Power management

• Shutdown now: sudo poweroff / sudo shutdown now

• Scheduled: sudo shutdown -h +10 / sudo shutdown -h 22:00

• Cancel: sudo shutdown -c

• Reboot: sudo reboot

• Suspend (RAM): sudo systemctl suspend

• Hibernate (swap): sudo systemctl hibernate

• Hybrid: sudo systemctl hybrid-sleep

• Suspend-then-hibernate: sudo systemctl suspend-then-hibernate

• logind config (/etc/systemd/logind.conf):

  HandleLidSwitch=suspend
  HandlePowerKey=poweroff
  IdleAction=suspend
  IdleActionSec=30min
  

• Reload: sudo systemctl restart systemd-logind

• Inhibit sleep: systemd-inhibit --what=sleep --who="my-script" --why="downloading" wget URL

• List inhibitors: systemd-inhibit --list

• CPU governor: cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor

• Set performance: echo performance | sudo tee /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor

• TLP (laptop power):

  sudo systemctl enable --now tlp
  sudo tlp-stat -b
  

Hostname

• Show: hostname / hostnamectl

• Set persistent: sudo hostnamectl set-hostname myarch

• Pretty hostname (UI display): sudo hostnamectl set-hostname "My Arch Workstation" --pretty

• Files: /etc/hostname, /etc/hosts (127.0.1.1 myarch).

cron vs systemd timer

Misc utilities

• Repeat command every 2s: watch -n 2 "df -h"

• Highlight changes: watch -d "free -h"

• Answer yes to prompts: yes | pacman -S package

• Low CPU priority: nice -n 19 make -j$(nproc)

• Low I/O priority (idle class): ionice -c3 rsync -a src/ dest/

• Timeout: timeout 30 wget URL

• Timeout with SIGKILL: timeout --signal=KILL 10 command

• Retry until success: until ping -c1 google.com; do sleep 1; done

• One-off scheduled: sudo systemd-run --on-active=30min /usr/local/bin/task.sh echo "reboot" | sudo at 02:00

• Bulk rename (perl-rename):

  rename 's/\.jpeg$/\.jpg/' *.jpeg
  rename 'y/A-Z/a-z/' *
  

• Random data: head -c 32 /dev/urandom | base64 openssl rand -hex 16

• Checksums: sha256sum file.txt sha256sum -c checksums.txt

• Copy with progress: rsync -ah --progress src dest

• HTTP server (current dir): python -m http.server 8000

• Base64: echo "hello" | base64 echo "aGVsbG8K" | base64 -d

• URL encode/decode (python):

  python -c "import urllib.parse; print(urllib.parse.quote('hello world'))"
  python -c "import urllib.parse; print(urllib.parse.unquote('hello%20world'))"
  

• JSON pretty: jq . data.json

• ISO from directory: mkisofs -o image.iso /path/to/dir

• Write ISO to USB: sudo dd if=archlinux.iso of=/dev/sdb bs=4M status=progress oflag=sync

• System info: fastfetch / neofetch

Useful one-liners

• Largest files everywhere: find / -type f -exec du -h {} + 2>/dev/null | sort -rh | head -20

• Kill all matching pattern: pkill -f "pattern"

• Tail a file: tail -f /var/log/pacman.log

• Listen / connect port: nc -l 8080 / nc host 8080

• Diff dir contents: diff <(ls dir1) <(ls dir2)

• Count files by extension: find . -type f | sed 's/.*\.//' | sort | uniq -c | sort -rn