Merge branch 'ShellCustomizations' into 'main'
Shell Customizations See merge request d_mcknight/blog-content!5
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2024-03-10_Shell-Customizations.md
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---
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date: 2024-03-27
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title: Shell Customizations and SSH
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tags:
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- homelab
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- linux
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- bash
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- development
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---
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Taking a detour from actual deployments, I recently started experimenting with different shell customizations.
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Until now, I've just used whatever default shell I have available on a given system, but a recent live stream
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from [Lawrence Systems](https://www.youtube.com/@LAWRENCESYSTEMS) mentioned shell customizations and tmux and
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lead me down this rabbithole. I'll also mention SSH configuration as its something that greatly helps my daily
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productivity and is tangentially related to some of my customizations.
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## tmux
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I only recently tried using tmux and I don't know why I went so long without it! The
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[tmux wiki](https://github.com/tmux/tmux/wiki) offers a complete explanation of what tmux is and all of the
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things it can do; in short, it manages processes and terminals. `tmux` has a pretty steep learning curve, but
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it only took me a day to get the hang of a few basic shortcuts; `ctrl`+`b`, or the "prefix key" enables
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interacting with `tmux` and then a command can be issued. Some of the commands I find most useful are:
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- `?` - Shows a list of tmux key bindings
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- `"` - Splits the window vertically and adds a pane
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- `up`/`down` - Navigates between vertical panes; if you hold `ctrl`+`b` then it moves the split up and down
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- `d` - Detaches the temux session; easy to remember since `ctrl`+`d` is how you detach an SSH session
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I'm not (yet) using tmux by default for local sessions, but I do have it enabled to run when I SSH into some
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systems; this is the primary reason I really like `tmux`. I can ssh into my server from my laptop and start a
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command (i.e.a very long rsync process) without worrying about disowning the process before my laptop goes
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to sleep; when I ssh back in, perhaps from another computer, I have the same terminal history and the same
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process attached. I will go into more detail in the "ssh" section of this post, but all I had to do is run
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`tmux new -A -s ssh_tmux` when I connect to attach a tmux session named `ssh_tmux`, creating it if it doesn't
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exist.
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## ssh
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For SSH keys, I have one key pair I use for personal systems and another for work. I won't go into detail about
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key management or key rotation and instead will focus on SSH configuration. My SSH config simply contains global
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config options and includes other configuration files for specific hosts. I find this makes it easier to manage
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hosts since I can group hosts in different files. My `~/.ssh/config` looks like:
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```
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Include config.d/*
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Host *
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AddKeysToAgent yes
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IdentitiesOnly yes
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```
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- `AddKeysToAgent` adds keys to my ssh agent so I don't need to enter a passcode after the first time I use a key
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- `IdentitiesOnly` prevents SSH from trying to infer an identity file to use if it isn't specified in SSH config
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or explicitly supplied as an argument.
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> You can find descriptions of all the SSH config options in the [BSD manpages](https://man.openbsd.org/ssh_config).
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A couple example hosts look like:
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```
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Host work.server
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HostName <server IP Address>
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User <remote username
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IdentityFile ~/.ssh/id_rsa_work
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RemoteCommand tmux new -A -s ssh_tmux
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RequestTTY yes
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...
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Host mcknight.unraid
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HostName 192.168.1.100
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User root
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IdentityFile ~/.ssh/id_rsa_home
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RemoteCommand tmux new -A -s ssh_tmux
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```
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- `RemoteCommand` is executed on the remote system upon SSH connection. This can cause some odd quirks since the
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command is executed immediately upon connection. I only ran into trouble if I needed to change a password upon
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connection (unlikely situation if you're connecting with SSH keys) and with rsync (more on that below). This
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can be overridden by connecting with `ssh mcknight.unraid -o RemoteCommand=None`.
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- `RequestTTY` I found was required on one Ubuntu Server in order for tmux to start properly. I don't know exactly
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why this is necessary, but it solved a problem.
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To work around rsync issues, I aliased the command in my `.bashrc`: `alias rsync="rsync -e 'ssh -o RemoteCommand=none'"`.
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This might cause some problems with fully local transfers, but I don't alias this on servers where I would move
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enough data around to necessitate using rsync.
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## BASH Configuration
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I use `bash` primarily since its available in pretty much every Linux distro, Windows, and MacOS (not that I use
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MacOS). I mostly use a standard `.bashrc` that ships with Mint, but I recently updated the PS1 and PS2 variables
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using [Tom from Lawrence Systems'](https://github.com/lawrencesystems/dotfiles/blob/master/.bash_profile) as
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inspiration.
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My shell prompt looks like:
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<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>
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<font color="#9E7199">└</font><font color="#06989A">$</font>
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</pre>
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And a snippet from .bashrc related to that:
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```shell
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color_off="\[\033[0m\]" # Text Reset
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# Regular Colors
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black="\[\033[0;30m\]"
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red="\[\033[0;31m\]"
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green="\[\033[0;32m\]"
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yellow="\[\033[0;33m\]"
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blue="\[\033[0;34m\]"
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purple="\[\033[0;35m\]"
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cyan="\[\033[0;36m\]"
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white="\[\033[0;37m\]"
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path_color=$blue
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chrome_color=$purple
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context_color=$cyan
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prompt_symbol=@ # 🚀💲
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prompt='\$'
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if [ "$EUID" -eq 0 ]; then # Change prompt colors for root user
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context_color=$red
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prompt_symbol=💀
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fi
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PROMPT_COMMAND='if [[ $? != 0 && $? != 130 ]];then echo "⚠️";fi'
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PS1="$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}${color_off} "
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PS2=$chrome_color'└>$color_off '
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export VIRTUAL_ENV_DISABLE_PROMPT=1
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```
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There's a lot going on in the prompt, but I will highlight pieces of it; keep in mind that the snippets below may
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not be valid on their own and that some of the color formatting may be lost as I cut up the long prompt string.
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- `PROMPT_COMMAND='if [[ $? != 0 && $? != 130 ]];then echo "⚠️";fi'` isn't part of the prompt string, but rather an
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expression evaluated before the prompt string. This renders a ⚠️ if the previous command fails and isn't just an
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empty command.
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- `[${context_color}\A${chrome_color}]` prints the current time in 24H format. Helpful if you open a terminal and
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want to quickly reference when you ran the last command and when it completed.
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- `${debian_chroot:+('${path_color}'$debian_chroot'${chrome_color}')─}`
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and `${VIRTUAL_ENV:+('${path_color}'$(realpath $VIRTUAL_ENV --relative-to $PWD --relative-base /home'${chrome_color}')─})`
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print an active chroot or Python venv path, if active. I print the venv path relative to the current directory
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if within `home`; I find this helpful when I have multiple projects to make sure I know which one I'm looking at.
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Note that I also specify `export VIRTUAL_ENV_DISABLE_PROMPT=1` to suppress the default `(venv)` prompt prefix.
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- `[${context_color}\u${chrome_color}${prompt_symbol}${context_color}\h${chrome_color}]` looks like the default shell,
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`user@hostname` except when root the `@` is replaced with `💀` as an extra visual reminder that its a root shell.
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- `(${path_color}\w${chrome_color})` shows the current shell path like the default shell
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- `\n${chrome_color}└${context_color}${prompt}${color_off} ` continues to the next line and inserts the `$` or `#`
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prompt, followed by a space.
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- `PS2=$chrome_color'└>$color_off '` updates the prefix used when there's a newline in a command. I like that this
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makes each line start vertically aligned and it keeps the chrome colored differently from the inputs.
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## Further Reading
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SSH, BASH, and tmux are all over a decade old with plenty of good documentation and write-ups that I've referenced.
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My current `.bashrc` is in [this gist](https://gist.github.com/d-mcknight/176899ca924b5b4cfdf7692e36ca568e) and
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I will try to keep that updated as I make changes; maybe one day I'll promote it to an actual repository with other
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config files.
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