diff --git a/knowledge base/homebrew.md b/knowledge base/homebrew.md
index c4bd28b..77c94d2 100644
--- a/knowledge base/homebrew.md	
+++ b/knowledge base/homebrew.md	
@@ -8,31 +8,39 @@
 /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/uninstall.sh)"
 
 # Search for formulae.
-brew search parallel
-brew search --cask gpg
+brew search 'parallel'
+brew search --cask 'gpg'
 
 # Install something.
-brew install gettext
-brew install --cask spotify
+brew install 'gettext'
+brew install --cask 'spotify'
 
-# Uninstall something
-brew uninstall --zap keybase
+# Uninstall something.
+brew uninstall --zap 'keybase'
 
 # Get formulae's dependencies.
 brew deps
-brew deps --installed azure-cli
+brew deps --installed 'azure-cli'
 brew deps --tree
 
 # Get information on formulae.
-brew info sponge
+brew info 'sponge'
 
-# Prevent a formula from upgrading.
-brew pin gnupg2
+# Prevent formulae from upgrading.
+brew pin 'gnupg2'
+
+# Add taps.
+# Only one at a time.
+brew tap 'homebrew/services'
+
+# Manage services.
+# Requires the 'homebrew/services' tap.
+brew services start 'openssl-osx-ca'
 
 # Bring an installation up to speed from a Brewfile.
 brew bundle
 brew bundle --global
-brew bundle --file $HOME/Brewfile --no-lock
+brew bundle --file "$HOME/Brewfile" --no-lock
 
 # Dump all installed casks/formulae/images/taps into a Brewfile in the current
 # directory.
diff --git a/knowledge base/mac os x.md b/knowledge base/mac os x.md
index 775031b..6dccbb0 100644
--- a/knowledge base/mac os x.md	
+++ b/knowledge base/mac os x.md	
@@ -75,6 +75,27 @@ defaults read /Library/Preferences/SystemConfiguration/com.apple.smb.server NetB
 scutil --get ComputerName
 /usr/libexec/PlistBuddy -c "Print :System:System:ComputerName" \
   /Library/Preferences/SystemConfiguration/preferences.plist
+
+# Get environment variables from inside launchd.
+launchctl getenv 'key'
+launchctl export
+
+# Set environment variables inside of launchd.
+launchctl setenv 'key' 'value'
+launchctl unsetenv 'key' 'value'
+
+# List all loaded jobs.
+launchctl list
+
+# List Mach bootstrap services only.
+launchctl bslist
+launchctl bstree
+
+# Start jobs.
+launchctl start 'job_label'
+
+# Stop jobs.
+launchctl stop 'job_label'
 ```
 
 ## Xcode CLI tools
@@ -106,8 +127,8 @@ CLI_TOOLS_LABEL="$(/usr/sbin/softwareupdate -l \
 ### Removal
 
 ```sh
-sudo rm -rf $(xcode-select -p)
-sudo rm -rf /Library/Developer/CommandLineTools
+sudo rm -rf "$(xcode-select -p)"
+sudo rm -rf '/Library/Developer/CommandLineTools'
 ```
 
 ### Upgrade
@@ -116,7 +137,7 @@ See [How to update Xcode from command line] for details.
 
 ```sh
 # Remove and reinstall.
-sudo rm -rf $(xcode-select -p)
+sudo rm -rf "$(xcode-select -p)"
 xcode-select --install
 ```
 
@@ -149,7 +170,7 @@ defaults write com.apple.finder AppleShowAllFiles TRUE
 ```sh
 # Retain ratio.
 # Save as different file.
-sips -Z 1000 -o resized.jpg IMG_20190527_013903.jpg
+sips -Z '1000' -o 'resized.jpg' 'IMG_20190527_013903.jpg'
 ```
 
 ## Boot keys cheatsheet
@@ -260,6 +281,7 @@ You can either:
 ## Further readings
 
 - [pam_reattach]
+- [launchctl man page]
 
 ## Sources
 
@@ -284,3 +306,4 @@ You can either:
 [mac startup key combinations]: https://support.apple.com/en-us/HT201255
 [using terminal to find your mac's network name]: https://www.tech-otaku.com/networking/using-terminal-find-your-macs-network-name/
 [xcode command line tools installation faq]: https://www.godo.dev/tutorials/xcode-command-line-tools-installation-faq
+[launchctl man page]: https://www.unix.com/man-page/osx/1/launchctl
diff --git a/knowledge base/openssl-osx-ca.md b/knowledge base/openssl-osx-ca.md
new file mode 100644
index 0000000..2dd6ac5
--- /dev/null
+++ b/knowledge base/openssl-osx-ca.md	
@@ -0,0 +1,32 @@
+# openssl-osx-ca
+
+1. [TL;DR](#tldr)
+2. [Further readings](#further-readings)
+3. [Sources](#sources)
+
+## TL;DR
+
+```sh
+# Install and configure.
+brew tap homebrew/services
+brew tap raggi/ale
+brew install openssl-osx-ca
+brew services start openssl-osx-ca
+
+# Run manually.
+openssl-osx-ca
+```
+
+## Further readings
+
+- [Homebrew]
+
+## Sources
+
+- [openssl-osx-ca]
+
+<!-- project's references -->
+[openssl-osx-ca]: https://github.com/raggi/openssl-osx-ca
+
+<!-- internal references -->
+[homebrew]: homebrew.md