rkoten's Unix notes

Basics

Files

Iterate over files in a directory

for file in *; do
  if [ -f "$file" ]; then  # Skip to include directories
    echo "$file"
  fi
done

List file permissions

ls -ld

• {read, write, execute} by {user, group, other}
• Read=4, Write=2, Execute=1; combination=sum.

Mount NTFS drives

1. lsblk -f lists available filesystems.
2. udisksctl mount -b /dev/X mounts specified block device.

NixOS note: make sure "ntfs" is listed under boot.supportedFilesystems in OS config.

Processes

Find a process by keyword

pgrep -il "keyword"

- OR -

ps aux | grep "keyword"

(ignore grep itself as it'll be included in the ps aux results).

Kill a process

• Gracefully by PID: kill <pid>
• Forcefully by PID: kill -9 <pid>
• Suspended process in the current shell: kill %1

Utils

• File description: file
• Hex dump: xxd (best piped through less).

Initial setup

Dual boot with Windows

Fix Windows timezone:

timedatectl set-local-rtc 1

Disabling Ubuntu update notifications

• (?) sudo chmod 000 /usr/bin/update-manager
• sudo chmod 000 /usr/bin/update-notifier
• Reboot

Networking

Network fileshare

1. sudo apt install samba smbclient
   [for Ubuntu/Nautilus] sudo apt install nautilus-share
   

2. Grant firewall permissions.

   sudo ufw allow 'Samba'
   

3. Create a network password for your user.

   sudo smbpasswd -a <username>
   

4. Reboot.
5. (Optional) Verify SMB service is running.

   systemctl status smbd
   

6. Access via smb://<ip-address> and use the full username@hostname combination as username when connecting.

Check active network interface

route -n get <any-ip> | grep interface
# e.g.
route -n get 1.1.1.1 | grep interface

Run a speed test (macOS)

networkquality

SSH via ghostty

When ssh-ing from ghostty into a machine that is unaware of ghostty's metadata, an Error opening terminal: xterm-ghostty. may occur. To fix, once in the remote shell:

export TERM=xterm-256color

Reference: https://ghostty.org/docs/help/terminfo

Nix specifics

Include a specific package inline

On the example of nix and nixos-rebuild from the unstable repo:

nix shell github:NixOS/nixpkgs/nixpkgs-unstable#{nix,nixos-rebuild}

Utils

Docker

Assume container name "image".

Build the container from Dockerfile in the current dir:

docker build -t image .

Run the built container, assume port 1337:

docker run [--rm] [-d] [--privileged] -p 1337:1337 [--name nickname] image

• --rm removes the container once it's stopped.
• -d runs it detached and gives back control over the shell.
• --privileged lifts capability limitations on the container (can do virtually everything that the host can).
• --name gives the container a nickname, for convenient referencing.

List existing (running and stopped) containers:

docker ps -a

From the listed containers in the step above, take the reference (hash or nickname) of the given container.

docker exec -it <reference> /bin/bash

When done:

docker stop <reference>

If --rm was not passed when running a container, to remove it after stopping:

docker rm <reference>

Gnome

Extensions

• Grand Theft Focus brings popup windows to focus instead of "is ready" notification.

GRUB

GRUB Customizer is a GUI for GRUB configuration.

sudo add-apt-repository ppa:danielrichter2007/grub-customizer
sudo apt install grub-customizer

ffmpeg

Reencode voice recording in Opus

Assume 24k output bitrate.

ffmpeg -i <audio-input> -c:a libopus -b:a 24k -ar 24k -ac 1 -application voip <audio-output.ogg>

Reencode video with rendered subtitles

Assume 1920x1080 output res, Avenir font @ size 16.

ffmpeg -i <video-input> -vf "scale=1920:1080:flags=lanczos:force_original_aspect_ratio=decrease,pad=1920:1080:(ow-iw)/2:(oh-ih)/2,subtitles=<subtitle-input>:force_style='Fontname=Avenir,Fontsize=16'" -ss <start timestamp hh:mm:ss> -t <duration hh:mm:ss> <video-output>

cpdf (Coherent PDF)

Manual: link

Combine PDFs

cpdf input1.pdf input2.pdf [inputN.pdf] -o output.pdf

raspbian

raspi-config

TODO