Merge branch 'ShellCustomizations' into 'main'

Shell Customizations

See merge request d_mcknight/blog-content!5

2024-03-10_Shell-Customizations.md

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+---
+date: 2024-03-27
+title: Shell Customizations and SSH
+tags: 
+  - homelab
+  - linux
+  - bash
+  - development
+---
+
+Taking a detour from actual deployments, I recently started experimenting with different shell customizations.
+Until now, I've just used whatever default shell I have available on a given system, but a recent live stream
+from [Lawrence Systems](https://www.youtube.com/@LAWRENCESYSTEMS) mentioned shell customizations and tmux and
+lead me down this rabbithole. I'll also mention SSH configuration as its something that greatly helps my daily
+productivity and is tangentially related to some of my customizations.
+
+## tmux
+I only recently tried using tmux and I don't know why I went so long without it! The 
+[tmux wiki](https://github.com/tmux/tmux/wiki) offers a complete explanation of what tmux is and all of the 
+things it can do; in short, it manages processes and terminals. `tmux` has a pretty steep learning curve, but
+it only took me a day to get the hang of a few basic shortcuts; `ctrl`+`b`, or the "prefix key" enables 
+interacting with `tmux` and then a command can be issued. Some of the commands I find most useful are:
+- `?` - Shows a list of tmux key bindings
+- `"` - Splits the window vertically and adds a pane
+- `up`/`down` - Navigates between vertical panes; if you hold `ctrl`+`b` then it moves the split up and down
+- `d` - Detaches the temux session; easy to remember since `ctrl`+`d` is how you detach an SSH session
+
+I'm not (yet) using tmux by default for local sessions, but I do have it enabled to run when I SSH into some
+systems; this is the primary reason I really like `tmux`. I can ssh into my server from my laptop and start a
+ command (i.e.a very long rsync process) without worrying about disowning the process before my laptop goes
+ to sleep; when I ssh back in, perhaps from another computer, I have the same terminal history and the same
+ process attached. I will go into more detail in the "ssh" section of this post, but all I had to do is run 
+ `tmux new -A -s ssh_tmux` when I connect to attach a tmux session named `ssh_tmux`, creating it if it doesn't 
+ exist.
+
+## ssh
+For SSH keys, I have one key pair I use for personal systems and another for work. I won't go into detail about
+key management or key rotation and instead will focus on SSH configuration. My SSH config simply contains global
+config options and includes other configuration files for specific hosts. I find this makes it easier to manage
+hosts since I can group hosts in different files. My `~/.ssh/config` looks like:
+```
+Include config.d/*
+Host *
+	AddKeysToAgent yes
+	IdentitiesOnly yes
+```
+- `AddKeysToAgent` adds keys to my ssh agent so I don't need to enter a passcode after the first time I use a key
+- `IdentitiesOnly` prevents SSH from trying to infer an identity file to use if it isn't specified in SSH config
+  or explicitly supplied as an argument.
+
+> You can find descriptions of all the SSH config options in the [BSD manpages](https://man.openbsd.org/ssh_config).
+
+A couple example hosts look like:
+```
+Host work.server
+	HostName <server IP Address>
+	User <remote username
+	IdentityFile ~/.ssh/id_rsa_work
+	RemoteCommand tmux new -A -s ssh_tmux
+ 	RequestTTY yes
+...
+Host mcknight.unraid
+	HostName 192.168.1.100
+	User root
+	IdentityFile ~/.ssh/id_rsa_home
+	RemoteCommand tmux new -A -s ssh_tmux
+```
+- `RemoteCommand` is executed on the remote system upon SSH connection. This can cause some odd quirks since the
+  command is executed immediately upon connection. I only ran into trouble if I needed to change a password upon
+  connection (unlikely situation if you're connecting with SSH keys) and with rsync (more on that below). This 
+  can be overridden by connecting with `ssh mcknight.unraid -o RemoteCommand=None`.
+- `RequestTTY` I found was required on one Ubuntu Server in order for tmux to start properly. I don't know exactly
+  why this is necessary, but it solved a problem.
+
+
+To work around rsync issues, I aliased the command in my `.bashrc`: `alias rsync="rsync -e 'ssh -o RemoteCommand=none'"`.
+This might cause some problems with fully local transfers, but I don't alias this on servers where I would move
+enough data around to necessitate using rsync.
+
+## BASH Configuration
+I use `bash` primarily since its available in pretty much every Linux distro, Windows, and MacOS (not that I use
+MacOS). I mostly use a standard `.bashrc` that ships with Mint, but I recently updated the PS1 and PS2 variables
+using [Tom from Lawrence Systems'](https://github.com/lawrencesystems/dotfiles/blob/master/.bash_profile) as
+inspiration.
+
+My shell prompt looks like:
+<pre><font color="#9E7199">┌──[</font><font color="#06989A">22:27</font><font color="#9E7199">]─[</font><font color="#06989A">d_mcknight</font><font color="#9E7199">@</font><font color="#06989A">MCKNIGHT-FW13</font><font color="#9E7199">]─(</font><font color="#1D6CBF">~</font><font color="#9E7199">)</font>
+<font color="#9E7199">└</font><font color="#06989A">$</font> 
+</pre>
+
+And a snippet from .bashrc related to that:
+```shell
+    color_off="\[\033[0m\]"  # Text Reset
+
+    # Regular Colors
+    black="\[\033[0;30m\]"
+    red="\[\033[0;31m\]"
+    green="\[\033[0;32m\]"
+    yellow="\[\033[0;33m\]"
+    blue="\[\033[0;34m\]"
+    purple="\[\033[0;35m\]"
+    cyan="\[\033[0;36m\]"
+    white="\[\033[0;37m\]"
+
+    path_color=$blue
+    chrome_color=$purple
+    context_color=$cyan
+    prompt_symbol=@  # 🚀💲
+    prompt='\$'
+    if [ "$EUID" -eq 0 ]; then # Change prompt colors for root user
+      context_color=$red
+      prompt_symbol=💀
+    fi
+    PROMPT_COMMAND='if [[ $? != 0 && $? != 130 ]];then echo "⚠️";fi'
+    PS1="$chrome_color┌──[${context_color}\A${chrome_color}]─"'${debian_chroot:+('${path_color}'$debian_chroot'${chrome_color}')─}${VIRTUAL_ENV:+('${path_color}'$(realpath $VIRTUAL_ENV --relative-to $PWD --relative-base /home)'${chrome_color}')─}'"[${context_color}\u${chrome_color}${prompt_symbol}${context_color}\h${chrome_color}]─(${path_color}\w${chrome_color})\n${chrome_color}└${context_color}${prompt}${color_off} "
+    PS2=$chrome_color'└>$color_off '
+
+    export VIRTUAL_ENV_DISABLE_PROMPT=1
+```
+There's a lot going on in the prompt, but I will highlight pieces of it; keep in mind that the snippets below may 
+not be valid on their own and that some of the color formatting may be lost as I cut up the long prompt string.
+
+- `PROMPT_COMMAND='if [[ $? != 0 && $? != 130 ]];then echo "⚠️";fi'` isn't part of the prompt string, but rather an 
+expression evaluated before the prompt string. This renders a ⚠️ if the previous command fails and isn't just an
+empty command.
+
+- `[${context_color}\A${chrome_color}]` prints the current time in 24H format. Helpful if you open a terminal and
+want to quickly reference when you ran the last command and when it completed.
+
+- `${debian_chroot:+('${path_color}'$debian_chroot'${chrome_color}')─}`
+and `${VIRTUAL_ENV:+('${path_color}'$(realpath $VIRTUAL_ENV --relative-to $PWD --relative-base /home'${chrome_color}')─})`
+print an active chroot or Python venv path, if active. I print the venv path relative to the current directory 
+if within `home`; I find this helpful when I have multiple projects to make sure I know which one I'm looking at.
+Note that I also specify `export VIRTUAL_ENV_DISABLE_PROMPT=1` to suppress the default `(venv)` prompt prefix.
+
+- `[${context_color}\u${chrome_color}${prompt_symbol}${context_color}\h${chrome_color}]` looks like the default shell, 
+`user@hostname` except when root the `@` is replaced with `💀` as an extra visual reminder that its a root shell.
+
+- `(${path_color}\w${chrome_color})` shows the current shell path like the default shell
+
+- `\n${chrome_color}└${context_color}${prompt}${color_off} ` continues to the next line and inserts the `$` or `#`
+prompt, followed by a space.
+
+- `PS2=$chrome_color'└>$color_off '` updates the prefix used when there's a newline in a command. I like that this
+makes each line start vertically aligned and it keeps the chrome colored differently from the inputs.
+
+## Further Reading
+SSH, BASH, and tmux are all over a decade old with plenty of good documentation and write-ups that I've referenced.
+My current `.bashrc` is in [this gist](https://gist.github.com/d-mcknight/176899ca924b5b4cfdf7692e36ca568e) and 
+I will try to keep that updated as I make changes; maybe one day I'll promote it to an actual repository with other
+config files.