Linux-Tech-Tips/linux-tips.md

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*This is a random collection of useful things I came across.
It's mostly distro-agnostic but sometimes specific for [pacman-based distros](https://en.wikipedia.org/wiki/List_of_Linux_distributions#Pacman-based).*
[TOC]
### 0. *Short example template.*
- Description: *What is this good for.*
- Requires: *Do you need any particular software (provide a link)?*
- How-to: *Straight forward description and maybe a code example.*
- *Detailled description if necessary.*
- `$ this is the actual code lol`
- Aditionally: *Anything else that might be important like additional ressources.*
### 1. Automatic clear cache.
- Description: Automatically move files older than a specific amount of time from your user's `~/.cache` directory to the trash.
- Requires: The [rmtrash](https://github.com/PhrozenByte/rmtrash) package and [anacron](https://www.youtube.com/watch?v=41Lay6ZPtRQ).
- How-to: Add the following line to `/etc/cron.daily/cache`.
- `find ~/.cache/* -mtime +7 -exec rmtrash -rf {} \;`
- This will move files older than 7 days in `~/.cache` to the trash every day.
- Additionally: This can also be done using regular `rm` instead of `rmtrash`.
### 2. Limit systemd journal size.
- Description: Limit the systemd journal to a specific size.
- Requires: Specific to systems using [systemd](https://systemd.io/).
- How-to: Edit `/etc/systemd/journald.conf` and change `SystemMaxUse=50M`.
- Additionally: [ArchWiki: systemd](https://wiki.archlinux.org/title/Systemd/Journal#Journal_size_limit).
- Additionally: This can also be achieved using `journalctl` and be [limited by time](https://wiki.archlinux.org/title/Systemd/Journal#Clean_journal_files_manually).
### 3. Syntax highlight for nano.
- Description: Enable syntax highlighting for nano.
- Requires: The [nano](https://www.nano-editor.org/) editor.
- How-to: Edit `~/.config/nano/nanorc` or to `/etc/nanorc` and add the following:
- `include "/usr/share/nano/*.nanorc"`.
- Additionally: [ArchWiki: Nano](https://wiki.archlinux.org/title/Nano#Syntax_highlighting).
### 4. Repeat a command using watch.
- Description: Repeat and watch a command in a custom interval.
- Requires: The [procfs](https://gitlab.com/procps-ng/procps) package.
- How-to: Use `watch` followed by your command.
- Example: `$ watch -n 1.0 "du -h -s ./$folder`
- This prints the summarized size of $folder in human-readable format every second.
- Additionally: ---
### 5. Repeat last command as su.
- Description: Repeat the last command using sudo.
- Requires: The [sudo](https://www.sudo.ws/) package.
- How-to: Just type `$ sudo !!` and the last command will be repeated using `sudo`.
- Additionally: ---
### 6. Prevent overwriting files.
- Description: Use alias for `rm`, `cp` and `mv`.
- How-to: Add the following alias into your `~/.bashrc`.
- Use *-interactive* option to get asked before overwriting files.
- `alias mv="mv -i"`
- Additionally: [ArchWiki: Core utilities](https://wiki.archlinux.org/title/Core_utilities#Preventing_data_loss).
### 7. Auto-clean package cache.
- Description: Automatically clean the pacman package cache using paccache.
- Requires: A [pacman-based distro](https://en.wikipedia.org/wiki/List_of_Linux_distributions#Pacman-based) and the [pacman-contrib](https://github.com/archlinux/pacman-contrib) package.
- How-to: Enable the paccache.timer.
- `$ systemctl enable paccache.time`
- Additionally: Edit the paccache.service in /usr/lib/systemd/system/ and change the command to e.g. keep the latest installed version and no uninstalled version of all packages: `ExecStart=/usr/bin/paccache -rk1 && /usr/bin/paccache -ruk0`
### 8. Passwordless SSH.
- Description: Connect to a remote maschine using SSH without a password.
- Requires: A SSH implementation like [TinySSH](https://tinyssh.org/).
- How-to: Generate a keypair and send the public key to the remote maschine's authorized keys.
- Generate a keypair: `$ ssh-keygen -t rsa`
- Send the key: `$ ssh-copy-id $remote-username@$remote-ip-address`
- Fill in the username and IP address of your remote maschine.
- For example: `$ ssh-copy-id foo@192.168.178.123`
- Additionally: Here's a more detailed [tutorial](https://www.hostinger.com/tutorials/how-to-setup-passwordless-ssh/).
### 9. Automatic clean orphaned packages.
- Description: Automatically remove orphaned packages.
- Requires: A pacman-based distribution and anacron.
- How-to: Add the following line to `/etc/cron.daily/orph`.
- `pacman -Qtdq | pacman -Rns -`
- Additionally:
### 10. Automatic retrieve latest mirrors.
- Description: Automatically retrieve the latest Arch Linux mirrors and write them to the mirrorlist.
- Requires: An Arch-based distro and [reflector](https://xyne.dev/projects/reflector/).
- How-to: Install reflector and enable the reflector.timer.
- `$ systemctl enable reflector.timer`
- Additionally: [ArchWiki: Reflector](https://wiki.archlinux.org/title/Reflector#systemd_timer).
### 11. Extract text containing keywords from any file.
- Description: This command will filter and sort text based on keyword from any file(s).
- Requires: [GNU Coreutils](https://www.gnu.org/software/coreutils/), [GNU grep](https://www.gnu.org/software/grep/)
- How-to:
- `$ cat ./*/files* | grep -e keyword1 -e keyword2 | sort -u | nl > file`
- `cat` will take any file(s), multiple files in multiple subdirectories can be specified.
- `grep -e` will look for any and/or all specified keywords.
- `sort -u` will sort the results alphabetically and remove duplicates.
- `nl` will add a number in front of every result (optionally).
- `>` will write everything in a specified file.
- Additionally: This is simply an example of how useful the coreutils can be, especially when used together.
### 12. Enable parallel downloads for pacman.
- Description: Enable parallel downloads for faster updates with pacman.
- Requires: A [pacman-based distro](https://en.wikipedia.org/wiki/List_of_Linux_distributions#Pacman-based).
- How-to: Edit pacman's config-file at `/etc/pacman.conf` and uncomment `ParallelDownloads` and add a number of parallel downloads like 5 or 10.
- `# nano /etc/pacman.conf`
- Additionally: [ArchWiki: Pacman](https://wiki.archlinux.org/title/Pacman#Enabling_parallel_downloads).
### 13. Enable smartd service.
- Description: Enable the smartd daemon to monitor SMART status and emit notifications to log.
- Requires: [smartmontools](https://archlinux.org/packages/?name=smartmontools)
- How-to:
- Enable the service `# systemctl enable smartd.service`
- Uncomment/add the following line to `/etc/smartd.conf`:
`DEVICESCAN -a`
- Additionally: [ArchWiki: S.M.A.R.T.](https://wiki.archlinux.org/title/S.M.A.R.T.#smartd)