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Collection of tips on Linux (mostly Debian/Ubuntu) helpful to me

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# linux-tips
Collection of tips on Linux (mostly Debian/Ubuntu) helpful to me

## Bash Keyboard Shortcuts
| Shortcut | Action |
|:---------|:-------|
| <kbd>Esc</kbd> + t | Swap the two _words_ before the cursor |
| <kbd>Ctrl</kbd> + r | Search command history |
| <kbd>Ctrl</kbd> + g | Cancel command history search without running command |
| <kbd>Ctrl</kbd> + l | Clear terminal screen |
| <kbd>Ctrl</kbd> + x | List possible filename completions |
| <kbd>Ctrl</kbd> + c | Cancels the running command |
| <kbd>Ctrl</kbd> + z | Suspends the running command |
| <kbd>Ctrl</kbd> + u | Deletes entire line _before_ the cursor |
| <kbd>Ctrl</kbd> + k | Deletes entire line _after_ the cursor |
| <kbd>Ctrl</kbd> + t | Swap the two characters before the cursor |
| <kbd>Ctrl</kbd> + d | Close the terminal |
| <kbd>Ctrl</kbd> + f | Go _forward_ one character |
| <kbd>Ctrl</kbd> + b | Go _back_ one character |
| <kbd>Ctrl</kbd> + a | Go to the _beginning_ of the line |
| <kbd>Ctrl</kbd> + e | Go to the _end_ of the line |
| <kbd>Ctrl</kbd> + w | Delete the _word_ before the cursor |
| <kbd>Ctrl</kbd> + y | Retrieves the last _word_ deleted or cut |
| <kbd>Ctrl</kbd> + xx | Toggle between current cursor position and start or end of line |
| <kbd>Alt</kbd> + u | Capitalize all letters in word after cursor |
| <kbd>Alt</kbd> + l | Lower case all letters in word after cursor |
| <kbd>Alt</kbd> + . | Use the last word of the last command |

[Reference1](https://ostechnix.com/list-useful-bash-keyboard-shortcuts/)

## Basic configuration for new Git repository
```bash
# Set user name and e-mail address (required to do 'commit')
git config [--global] user.email "user@domain.com"
git config [--global] user.name "User Name"

# Store/cache password
git config [--global] credential.helper store
git pull

# Set the remote repository (for existing code)
git remote add origin https://github.com/user/repo_name.git
```

## Add existing user to existing group
```bash
sudo usermod -a -G groupnames username
```
`-a` - append groups to group user belongs to (instead of overwrite).
`groupnames` - a comma-separated (no spaces!) list of group names to add user to.
User must log out and back in for group membership updates to be applied.
[Reference](http://askubuntu.com/a/79566)

## Swap the `Caps Lock` and `(Right) Control` keys on keyboard
The level of configurability in Linux is simply amazing.  With the venerable [`xmodmap`](https://linux.die.net/man/1/xmodmap) utility, keyboard remapping is a snap. Just add these lines to your `$HOME/.xmodmap` file to swap the `Caps Lock` and `(Right) Control` keys.
```bash
remove Lock = Caps_Lock
remove Control = Control_R
keysym Control_R = Caps_Lock
keysym Caps_Lock = Control_R
add Lock = Caps_Lock
add Control = Control_R
```

## Enter Unicode characters with keyboard in Linux
In most applications in Linux, including at the command line, to enter a [Unicode](https://www.rapidtables.com/code/text/unicode-characters.html) character, hold down `<LeftCtrl>` and `<Shift>` plus _u_ and enter the 2- or 4-character *hexadecimal* Unicode code. When you release `<LeftCtrl>` and `<Shift>`, the character will be displayed. For example, to enter superscript 2 (²), which is Unicode 00B2, type `<LeftCtrl>`+`<Shift>`+_u_+B2; for the trademark symbol (™), which is Unicode 2122, type `<LeftCtrl>`+`<Shift>`+_u_+2122. Note that you can use the numeric keys across the top of the keyboard or on the numeric keypad (with NumLock enabled).
[Reference1](https://twitter.com/brianredbeard/status/1371862052797517825)
[Reference2](https://old.reddit.com/r/linux/comments/m6dbbm/til_on_linux_one_can_type_arbitrary_unicode/)

## Install packages required to build application from source in Ubuntu/Debian
If you want to build an application from source for a new version of an application that has a Ubuntu/Debian package, you can use the `build-dep` utility to install the required dependencies in one go.
```bash
sudo apt-get build-dep PKG_NAME
```
where `PKG_NAME` is the package name, such as `vim-common`.
[Reference](https://wiki.debian.org/BuildingTutorial#Get_the_build_dependencies)

## "Safe" alternative to bypassing password prompt for `sudo`
To avoid getting prompted for password when running commands with [`sudo`](https://manpages.ubuntu.com/manpages/precise/en/man8/sudo.8.html), one common option is to append `NOPASSWD:ALL` to your user name in the `/etc/sudoers` file. Obviously, this is a security risk. Instead, you can run the `sudo` command with the `-s` ("session") flag to allow the `sudo` session to be persistent until your close the terminal (end the session). To explicitly end the session run `sudo -k` ("kill").
[Reference](https://vitux.com/how-to-specify-time-limit-for-a-sudo-session/)

## Change default editor for `visudo`
By default, Linux systems use the `$VISUAL` or `$EDITOR` environment variables (usually defined in your `~/.bashrc` file or `/etc/profile`) as the default editor the [`visudo`](https://linux.die.net/man/8/visudo) command. If you'd prefer to use a different editor, such as [nano](https://nano-editor.org/), you can use either of these methods.
1. To **temporarily** use a different editor, run:
```console
$ sudo EDITOR=/path/to/editor visudo
```
For example, to use `nano`, you would run:
```console
$ sudo EDITOR=nano visudo
```
2. To **permanently** change the default editor, edit the `/etc/sudoers` file (you can use the _temporary_ method above!) and add the following line to the file near the top, but _after_ `Defaults env_reset`:
```console
Defaults    editor=/path/to/editor
```

[Reference1](https://unix.stackexchange.com/questions/4408/how-to-set-visudo-to-use-a-different-editor-than-the-default-on-fedora)

## Upgrade Ubuntu to non-LTS version via command line
By default, most installations of Ubuntu are configured to upgrade only to LTS (long-term support) distribution releases, which come out every two years (e.g., 18.04, 20.04, etc.).  If you want to upgrade your Ubuntu installation to a non-LTS release (e.g., from Bionic Beaver [18.04] to Eoan Ermine [19.10]) you can do so via command line.  Here's how.

### Update current release to latest patches
```bash
sudo apt-get install update-manager-core -y
sudo apt-get update && sudo apt-get upgrade -y && sudo apt-get dist-upgrade -y
```

### Update upgrade manager to `normal` (non-LTS) setting
```bash
sudo sed -i 's/Prompt=lts/Prompt=normal/g' /etc/update-manager/release-upgrades
```

### Change distribution reference to desired version codename* and disable third-party repositories (PPAs)
```bash
sudo sed -i 's/bionic/eoan/g' /etc/apt/sources.list
sudo sed -i 's/^/#/' /etc/apt/sources.list.d/*.list
```
Replace `bionic` and `eoan` above with the current and desired distribution version codenames, respectively, as appropriate.
*See [here](https://en.wikipedia.org/wiki/Ubuntu_version_history) for list of Ubuntu distribution codenames with associated version numbers.

### Run the upgrade, remove unneeded packages, and reboot to complete update
```bash
echo '* libraries/restart-without-asking boolean true' | sudo debconf-set-selections
sudo apt-get update && sudo apt-get upgrade -y && sudo apt-get dist-upgrade -y -o Dpkg::Options::=--force-confdef -o Dpkg::Options::=--force-confnew
sudo apt-get autoremove -f -y && sudo apt-get clean -y
sudo shutdown -r now
```
See [this article](https://unix.stackexchange.com/questions/22820/how-to-make-apt-get-accept-new-config-files-in-an-unattended-install-of-debian-f) for details about forcing use of new/package maintainer's version of configuration files.  For additional details refer to [this article](https://serverfault.com/a/858361).

### Confirm new release version
```bash
lsb_release -a
```

### Re-enable third-party repositories (PPAs) and change them to the new version codename
```bash
sudo sed -i '/deb/s/^#//g' /etc/apt/sources.list.d/*.list
sudo sed -i 's/bionic/eoan/g' /etc/apt/sources.list.d/*.list
sudo apt-get update && sudo apt-get upgrade -y
```
If you get any errors that a repository can't be found (e.g., `The repository 'http://linux.dropbox.com/ubuntu eoan Release' does not have a Release file.`), then you will need to revert these individual repositories to the earlier distribution version codename in `/etc/apt/sources.list.d` directory.

[Reference](https://www.linuxbabe.com/ubuntu/upgrade-ubuntu-18-04-to-ubuntu-19-10-from-command-line)

## Bash script to toggle touchpad on and off
If you use an external mouse with your laptop, you probably want to disable your touchpad when the mouse is plugged in. Here's how to create a simple Bash script to toggle the touchpad on and off.

At the Bash prompt, run this command to list _all_ of your input devices, such as the keyboard, mouse, and touchpad:
```bash
$ xinput
⎡ Virtual core pointer                          id=2    [master pointer  (3)]
⎜   ↳ Virtual core XTEST pointer                id=4    [slave  pointer  (2)]
⎜   ↳ USB Optical Mouse                         id=10   [slave  pointer  (2)]
⎜   ↳ **SynPS/2 Synaptics TouchPad                  id=12** [slave  pointer  (2)]
```
In this example, the touchpad, has device ID **12**. Next, we check the status (enabled or disabled) for this device:
```bash
$ xinput -list-props 12 | grep "Device Enabled"
    Device Enabled (**116**):   **1**
```
Here, the **1** means that the touchpad is _enabled_. Create a script named `touchpad.sh` with the following contents and replace **12** and **116** with the appropriate values for your machine:
```bash
#!/bin/bash
if xinput list-props **12** | grep "Device Enabled (**116**):.*1" >/dev/null
then
  xinput disable **12**
  notify-send -u low -i mouse "Touchpad disabled"
else
  xinput enable **12**
  notify-send -u low -i mouse "Touchpad enabled"
fi
```
Copy `touchpad.sh` to a directory in your `$PATH` and make it executable (`chmod +x touchpad.sh`). Simply run it anytime that you want to toggle the touchpad on or off.

[Reference](http://tuxdiary.com/2016/08/15/toggle-touchpad-ubuntu-16-04/)

## Disable GPG checking for third-party repositories (PPAs)
When using third-party repositories (PPAs), you typically need to install GPG key. If you have trouble with GPG keys, you can configure the repository, in `/etc/apt/sources.list` or the custom configuration file in `/etc/apt/sources.list.d/` by adding `trusted=yes` or `allow-insecure=yes`. The difference between them is that `allow-insecure=yes` will prompt you before allowing you to install, but `trusted=yes` won't.

For example, here's the setting used with the MongoDB repository:
```bash
deb [ arch=amd64 `allow-insecure=yes ] http://repo.mongodb.org/apt/ubuntu bionic/mongodb-org/4.0 multiverse
```
[Reference](https://unix.stackexchange.com/questions/198000/bypass-gpg-signature-checks-only-for-a-single-repository)

## Reset 'root' password for MySQL Server (version 8.0+)
If you install [MySQL Server 8.0](https://dev.mysql.com/doc/refman/8.0/en/) or later in Ubuntu without specifying the `root` password, you can set (reset) it as follows.

Run `mysql` utility with `root` account without password:
```bash
sudo mysql
```
(Note: This only works if no `root` password is set.)

At the MySQL prompt, use the [`ALTER USER`](https://dev.mysql.com/doc/refman/8.0/en/alter-user.html) command to set the desired password.  It is important to specify the authentication plugin as [`mysql_native_password`](https://dev.mysql.com/doc/refman/8.0/en/native-pluggable-authentication.html) to allow applications such as [phpMyAdmin](https://www.phpmyadmin.net/) to connect (see also [here](https://github.com/phpmyadmin/phpmyadmin/issues/14220)).
```bash
ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY 'new_root_password';
FLUSH PRIVILEGES;
```

Restart MySQL service:
```bash
sudo systemctl restart mysql
```

You should now be able to log in to MySQL from command prompt with the new password:
```bash
mysql -u root -pnew_root_password
```

[Reference](https://askubuntu.com/questions/766900/mysql-doesnt-ask-for-root-password-when-installing/766908#766908)

## Mount AWS S3 Bucket Using `s3fs`
`s3fs` is a [FUSE](http://manpages.ubuntu.com/manpages/precise/man8/mount.fuse.8.html) [(File System in Userspace)](https://en.wikipedia.org/wiki/Filesystem_in_Userspace) extension which allows you to mount an Amazon Web Services (AWS) S3 bucket as native local file system. In other words, no specialized tools are required.

We will use `s3fs` package from the Ubuntu repositories. You can install `s3fs` by building it from source; see [`s3fs` Github repository](https://github.com/s3fs-fuse/s3fs-fuse) for details.

Switch to the `root` user *before* performing the other steps:
```bash
sudo su -
```

Install `s3fs`:
```bash
apt-get install -y s3fs
```

Create the *system* `s3fs` password file using the appropriate AWS S3 credentials (access key ID and secret access key).
```bash
echo AWS_ACCESS_KEY_ID:AWS_SECRET_ACCESS_KEY > /etc/passwd-s3fs
chmod 600 /etc/passwd-s3fs
```
`/etc/passwd-s3fs` can contain multiple sets of credentials (access key ID and secret access key pair combinations) with each on its own line in the file.

Create file system directories to mount S3 bucket and for caching S3 bucket contents. The cache directory is optional, but will improve performance when using S3 bucket with large number of files.
```bash
mkdir /tmp/cache
mkdir /mnt/s3-bucket
chmod 777 /tmp/cache /mnt/s3-bucket
```

Mount the S3 bucket using `s3fs`. (Note: This mount is temporary/non-persistent. See below for mounting the file system on boot using `/etc/fstab`.)
```bash
s3fs s3-bucket-name /mnt/s3-bucket -o passwd_file=/etc/passwd-s3fs -o allow_other,use_cache=/tmp/cache
```
Replace `s3-bucket-name` with the desired S3 bucket for the credentials specified in `/etc/passwd-s3fs` from above. Note that `rw` means to mount the file system as "read-write" (the default setting); if you want to mount as "read-only", change this to `ro`.

Test the S3 bucket file system mount. You should see a "standard" file system listing. And, of course, you can use GUI file managers by navigating to `/mnt/s3-bucket`.
```bash
ls -lrt /mnt/s3-bucket
```

To mount the S3 bucket as your (non-root) user ID, at a *regular* (non-root) command prompt run `id ${USER}`. You should see something *like*:
```bash
id ${USER}
uid=1000(tim) gid=1000(tim) groups=1000(tim),4(adm),24(cdrom),27(sudo),30(dip),33(www-data),46(plugdev),107(input),121(lpadmin),131(lxd),133(sambashare),998(docker)
```
Use the `uid` and `gid` values above to run `s3fs`:
```bash
s3fs s3-bucket-name /mnt/s3-bucket -o passwd_file=/etc/passwd-s3fs -o allow_other,use_cache=/tmp/cache,uid=1000,umask=077,gid=1000
```
If you get an error about not being allowed to use `allow_other` as regular user, you will need to uncomment the `user_allow_other` line in `/etc/fuse.conf` FUSE configuration file.

To configure your system to automatically ("permanently") mount the S3 bucket when it boots, do the following. (This assumes that you are still logged in as `root` user.)
```bash
echo s3fs#s3-bucket-name /mnt/s3-bucket fuse _netdev,rw,nosuid,nodev,allow_other,nonempty,uid=1000,umask=077,uid=1000 0 0 >> /etc/fstab
```
Mount (re-mount) the file system to ensure that it works properly.
```bash
mount -a
```

That\'s it! Now you can transparently work with your S3 buckets just like they are local files.

[Reference1](https://sysadminxpert.com/how-to-mount-s3-bucket-on-linux-instance/)
[Reference2](https://winscp.net/eng/docs/guide_amazon_s3_sftp#mounting)

## Fix HP Pavilion Laptop lockup/freeze problem on idle/inactivity in Linux
Some HP Pavilion laptops experience problems with freezing after inactivity timeouts or other idle conditions. Some or all of the following items can _help_ prevent such problems.

- Disable power saving features.
- Disable screensaver and screen lock features.
- Add [kernel boot parameters](https://wiki.ubuntu.com/Kernel/KernelBootParameters) to GRUB boot menu options.
    - `noapic` - Disable APIC (Advanced Programmable Interrupt Controller) support.
    - `idle=nomwait` - Disable "mwait" for CPU idle state.

[Reference1](https://stackoverflow.com/questions/53001737/what-do-boot-option-noapic-and-noacpi-actually-do)

## Display time and time zone details for system
For a quick check of the time and time zone details of your Linux system, run the _`timedatectl`_ command. It will show you the current local time, UTC time, RTC (real-time clock from BIOS) and the time zone, along with some additional details. The command can also be used to change these settings. See the [_`timedatectl`_](https://man7.org/linux/man-pages/man1/timedatectl.1.html) `man` page for more information.

***

## Show processor architecture information and use in shell script
Many times in a shell script, you may need to differentiate between whether your Linux platform is 32-bit or 64-bit and which processor type/architecture is used. Here are a few commands you can use to get such information.

[Reference1](https://www.tecmint.com/check-linux-cpu-information/)
[Reference2](https://www.linuxtechi.com/server-cpu-architecture-linux/)
[Reference3](https://stackoverflow.com/questions/45125516/possible-values-for-uname-m/45125525#45125525)

## Tidy up your Linux command line history with `HISTIGNORE`
If you use the Linux command line often, one of the greatest features is the [`history`](https://www.man7.org/linux/man-pages/man3/history.3.html) of commands run. Simply press the up and down arrows to navigate backward and forward through the commands or hit <kbd>Ctrl</kbd>+R to search. However, if you navigate around a lot and list directory contents, your history can filled with extra commands that you aren't likely to want to from history, since they are simple enough to just run again. To prevent history from adding these to your command history, just add the `HISTIGNORE` variable to your `.bashrc` with a list of the commands to ignore separated with colons (`:`). Here's an example:
```bash
HISTIGNORE="ls:ls -lrt:[bf]g:history*:exit:*shutdown*:*reboot*:[ \t]*"
```
In this example, we ignore `ls` by itself and `ls -lrt`, the `bg` and `fg` commands, `exit`, and anything _starting with_ `history`. Likewise, you can see that we've included "dangerous" commands like `shutdown` and `reboot` that we probably don't want to accidentally run when quickly scrolling through a long history list. And, finally, `[ \t]*` means to ignore any command that you enter that starts with a <kbd>Space</kbd> or <kbd>Tab</kbd> so that you can selectively run a command and have it ignored in the history.

## Configure remote access on Ubuntu with XRDP
Historically, remote access on Linux was handled through the [VNC (Virtual Network Computing)](https://en.m.wikipedia.org/wiki/Virtual_Network_Computing) platform, such as with [x11vnc](https://github.com/LibVNC/x11vnc). However, recently, the [Remote Desktop Protocol (RDP)](https://en.m.wikipedia.org/wiki/Remote_Desktop_Protocol) developed for Microsoft Windows has gained popularity on Linux using the [XRDP](https://xrdp.org/) tool. Here's how to set it up on Ubuntu.

1. Install XRDP from the Ubuntu repositories.
   ```
   $ sudo apt-get install -y xrdp dbus-x11
   ```
2. After installation, Ubuntu will automatically launch the XRDP service. To confirm that it launched properly, run:
   ```
   $ sudo systemctl status xrdp
   ```
   You should see output similar to the following. The main thing to confirm is that it shows that the service is `active (running)` next to `Active`.
   ```
   ● xrdp.service - xrdp daemon
     Loaded: loaded (/lib/systemd/system/xrdp.service; enabled; vendor prese>
     Active: active (running) since Thu 2021-07-22 06:37:19 CDT; 29min ago
       Docs: man:xrdp(8)
             man:xrdp.ini(5)
    Process: 58107 ExecStartPre=/bin/sh /usr/share/xrdp/socksetup (code=exit>
    Process: 58115 ExecStart=/usr/sbin/xrdp $XRDP_OPTIONS (code=exited, stat>
   Main PID: 58116 (xrdp)
      Tasks: 2 (limit: 8740)
     Memory: 16.6M
     CGroup: /system.slice/xrdp.service
             ├─58116 /usr/sbin/xrdp
             └─58124 /usr/sbin/xrdp
    ```
3. XRDP uses the `/etc/ssl/private/ssl-cert-snakeoil.key` SSL certificate file for authentication. Access to this file is limited to members of the `ssl-cert` group, so we must add the `xrdp` user to that group with this command:
   ```
   $ sudo adduser xrdp ssl-cert
   ```
4. To ensure that XRDP service is enabled, so that it starts on system boot, run:
   ```
   $ sudo systemctl enable xrdp
   ```
   As in step #2 above, you can check the status again to ensure that it's running and `enabled`.
5. To avoid an authentication warning on the Ubuntu machine after logging in (see step #5 below), we must add a [Policy Kit](https://www.freedesktop.org/software/polkit/docs/latest/) rule, as indicated below.
   ```
   $ sudo nano /etc/polkit-1/localauthority.conf.d/02-allow-colord.conf

polkit.addRule(function(action, subject) {
       if ((action.id == "org.freedesktop.color-manager.create-device" || action.id == "org.freedesktop.color-manager.create-profile" || action.id == "org.freedesktop.color-manager.delete-device" || action.id == "org.freedesktop.color-manager.delete-profile" || action.id == "org.freedesktop.color-manager.modify-device" || action.id == "org.freedesktop.color-manager.modify-profile") && subject.isInGroup("{group}"))
       {
           return polkit.Result.YES;
       }
   });
   ```
   Restart the xrdp service for the change to take effect.
   ```
   $ sudo systemctl restart xrdp
   ```
6. Connect to your Ubuntu machine from another machine. If you are connecting from a Windows machine, you can use the standard Remote Desktop client (Start --> Windows Accessories --> Remote Desktop Connection _or_ Start --> Run --> mstsc.exe). Enter the IP address or hostname of your Ubuntu machine to connect. In a few seconds, you'll be prompted to log in; log in using the same **Ubuntu** username and password that you usually use. (You may also be prompted about SSL certificate validation, which you will need to accept.)

For connecting from another Ubuntu (or other Linux) machine, there are various RDP clients that you can use, including:
      - [Remmina](https://remmina.org/)*
      - [Vinagre](https://wiki.gnome.org/Apps/Vinagre)*
      - [TigerVNC](https://tigervnc.org/)* - To use TigerVNC with RDP, enter the IP address or hostname in the _viewer_ connection window followed by **:3389**. This means to connect on TCP port 3389, which is the port that RDP listens on.
      - [KRDC](https://apps.kde.org/krdc/)*
      - [X2Go](https://wiki.x2go.org/doku.php)*
      *Indicates that these are available in standard Ubuntu repositories (i.e., install using `sudo apt-get install`).
7. If you get a black (blank) screen on the remote machine after logging in remotely, you'll need to make a simple adjustment on the Ubuntu machine (the one that you are accessing remotely) in the script to launches the X11 window manager for XRDP. Do the following:
   ```
   sudo nano /etc/xrdp/startwm.sh
   ```
   Add the lines below right _below/after_ `if` block concerning `/etc/profile` near the bottom of the file.
   ```
   unset DBUS_SESSION_BUS_ADDRESS
   unset XDG_RUNTIME_DIR
   ```
   After making the change, the file should looking something like this:
   ```
   ...
   if test -r /etc/profile; then
           . /etc/profile
   fi

unset DBUS_SESSION_BUS_ADDRESS
   unset XDG_RUNTIME_DIR

test -x /etc/X11/Xsession && exec /etc/X11/Xsession
   exec /bin/sh /etc/X11/Xsession
   ```
   Finally, restart and enable the `xrdp` service to ensure the change takes effect.

[Reference1](https://linuxize.com/post/how-to-install-xrdp-on-ubuntu-18-04/)
[Reference2](https://www.tecmint.com/install-xrdp-on-ubuntu/)
[Reference3](https://linoxide.com/xrdp-connect-ubuntu-linux-remote-desktop-via-rdp-from-windows/)

## Prevent laptop from suspending when closing lid in Linux
If you have an old laptop that you typically access remotely (i.e., via VNC or RDP), then usually you will want to close the lid, but not have the device suspend, so that you can still connect remotely. Some Linux desktop environments (DE) have GUI options to do this, but many don't and, even those that do, use a variety of different techniques (e.g., power management, login, etc.). Here's the most reliable way to do it.
1. Edit the `logind` service configuration file as root.
   ```
   $ sudo nano /etc/systemd/logind.conf
   ```
2. Locate the lines under `[Login]` section that _start_ with `HandleLidSwitch` and uncomment them (remove the `#` at the start of the line, if any) and set the value to either `lock` (preferred) or `ignore`. (The current values, as commented out, are the defaults.) The `lock` setting will turn off the display and lock the machine, which will require you to enter your password when you open the lid, while `ignore` does nothing when you close the lid.
   ```
   HandleLidSwitch=lock
   HandleLidSwitchExternalPower=lock
   HandleLidSwitchDocked=ignore
   ```
3. Save the file and _reboot_ the machine for the changes to take effect. (You can actually just restart the `logind` service \[i.e., `sudo systemctl restart logind`\]. However, this will have the effect of logging you out.]

## Change screen resolution in Linux in running in Windows HyperV VM
When running Linux in a Windows HyperV VM, typically, the _Display_ configuration in the Linux instance will not have any provision to change the screen resolution. To change the resolution, you can adjust it via a command-line parameter in Grub. Edit the `/etc/default/grub` file as `root` user and append `video=hyperv_fb:1152x864` to the `GRUB_CMDLINE_LINUX_DEFAULT` and `GRUB_CMDLINE_LINUX` settings. You can choose whatever resolution you prefer, such as 1024x768, 1900x1200, etc. For example:
```
GRUB_CMDLINE_LINUX_DEFAULT="quiet nosplash video=hyperv_fb:1152x864"
```
Save the `/etc/default/grub` file and update the Grub configuration:
```
sudo update-grub
```
The changes will take effect the next time you reboot the HyperV VM.

[Reference](https://arcanecode.com/2020/12/28/adjust-the-screen-resolution-of-an-ubuntu-hyper-v-virtual-machine/)

## Launch `tmux` automatically when opening terminal/shell
If you typically run `tmux` immediately after opening a new terminal window or interactive shell, you can make this automatic. Just add the following lines to your `.bashrc` or `.bash_profile`.
```bash
# Start tmux automatically if interactive session and not already running
if command -v tmux > /dev/null; then
    [[ $- == *i* ]] && [[ ! $TERM =~ screen ]] && [[ -z $TMUX ]] && exec tmux new-session
fi
```

## Rebase local Git repository from upstream
In some instances, you will have a fork of Git repository that has significantly diverged from the `upstream` original. In this scenario, it is often simplest (or, at least, convenient) to `rebase` the local repository from the `upstream`. Here's how to do this.
1. Ensure that you have the `upstream` repository configured for your local repository.
```bash
git remote -v
```
This should display something like:
```bash
upstream <upstream-repo-url>.git (fetch)
upstream <upstream-repo-url>.git (push)
```
If the `upstream` repository is **not** displayed, then it should be added by running:
```bash
git remote add upstream <upstream-repo-url>.git
```
2. Change to your `main` (`master`) branch and fetch from upstream `main`.
```bash
git checkout main
git fetch upstream main
```
3. Overwrite the current local `main` from the upstream `main`:
```bash
git rebase upstream/main
```
4. Now, you must decide if you want to merge changes from your **remote** `main` or overwrite them with the rebased update from the `upstream` repository.
 a. If you want to merge changes from your **remote** `main`:
 ```bash
 git pull origin main
 ```
 You will be prompted to merge and enter a commit message. If any merge conflicts occur, you must resolve them.
 b. If you want to overwrite your **remote** `main` changes:
 ```bash
 git push -u origin main --force
 ```

Your local and remote `main` branches forked from `upstream` are now synced with `upstream` and you can proceed with additional work against it.

[Reference1](https://timonweb.com/misc/how-to-update-a-forked-repo-from-an-upstream-with-git-rebase-or-merge/)

## Extract files from various types of archives at command prompt
In most cases, I prefer to use the [`dtrx`](https://github.com/dtrx-py/dtrx) tool to extract archives. It automatically determines the archive type and extracts the file based on the determined type. However, if you are on a machine that doesn't have `dtrx`, it's useful to know the common commands to extract most archives.

Notes:
- The [`tar`](https://man7.org/linux/man-pages/man1/tar.1.html) command can include the `v` option for `verbose` for additional details. For example, `tar xzvf` for verbose option when extracting a `tar.gz` archive.
- These commands will extract the files in the **current** directory. To extract using `tar` into a specific directory use the `-C` option with the desired fully-qualified path. For example, `tar xzf file.tar.gz -C ~/Documents`.
- Typically, `tar` will auto-detect the compression format, if any, used in an archive, so you can usually simply use `tar xf` on most any `tar` archive and it will extract it properly. (The `zstd` format is one notable exception.)

[Reference1](https://linuxopsys.com/topics/tar-command-in-linux)  
[Reference2](https://linuxize.com/post/how-to-create-and-extract-archives-using-the-tar-command-in-linux/)

### An `extract()` shell function for decompressing archives
Using the rules specified above, we can build a bash shell function to extract most of the common archives in Linux. Just add this function to your `.bashrc` or `.bash_profile` configure file in your home directory. And ensure that you have the appropriate decompression tools installed; most Linux distributions already have them. Here are the commands to install them on a few common Linux distributions.
- Ubuntu/Debian/Linux Mint
```bash
sudo apt install -y zlib1g bzip2 zstd xz-utils 7zip unrar-free tar tarlz gzip
```
- CentOS/Redhat Linux/Fedora
```bash
sudo dnf install
```
- Archlinux/EndeavourOS
```bash
sudo pacman -
```

```bash
# Extract common archive files by file extension
function extract() {
    if [ -f $1 ] ; then
        case $1 in
#            *.tar.gz|*.tgz)     tar xzf $1          ;;
#            *.tar|*.tar.xz)     tar xf $1           ;;
#            *.tar.bz2|*.tbz2)   tar xjf $1          ;;
#            *.xz)               unxz $1             ;;
#            *.zip)              unzip $1            ;;
#            *.Z)                uncompress $1       ;;
#            *.tar.zst)          tar -I=unzstd xf $1 ;;
#            *.zst)              unzstd $1           ;;
#            *.7z)               7z x $1             ;;
        esac
    else
        echo "'$1' is not valid archive file."
    fi
}
```

## Best practices for command line `history`
One of the most powerful, but also most hidden features of the Linux/Unix command line is the [`history`](https://www.gnu.org/software/bash/manual/bash.html#Using-History-Interactively) command. The most commonly used features of the command history are:
| Shortcut | Action |
|:---------|:-------|
|

Generally, the defaults work well, but with a few simple tweaks, you can supercharge

## Toggle Synaptics Touchpad On/Off
The Synaptics touchpad can quickly and simply be toggled on and off at the command line using the `synclient` utility.
```bash
# Disable touchpad
synclient TouchpadOff=1

# Enable touchpad
synclient TouchpadOff=0

[Reference](https://askubuntu.com/a/67721)

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