Added user management-related notes to the knowledge base

knowledge base/useradd.md

@@ -0,0 +1,39 @@
+# Useradd
+
+Create a new user.
+
+## TL;DR
+
+```shell
+# Create a new user.
+sudo useradd username
+sudo useradd -p encryptedPassword username
+
+# Create a new user with the specified user ID.
+sudo useradd --uid id username
+
+# Create a new user with the specified expiration date.
+sudo useradd -e 2022-10-10 username
+
+# Create a new user with the specified shell.
+sudo useradd --shell path/to/shell username
+
+# Create a new user belonging to additional groups.
+sudo useradd --groups group1,group2,... username
+
+# Create a new user with or without its default home directory.
+sudo useradd --create-home username
+sudo useradd --no-create-home username
+
+# Create a new user with the home directory filled by template directory files.
+sudo useradd --skel path/to/template_directory --create-home username
+
+# Create a new system user without the home directory.
+sudo useradd --system username
+```
+
+## Sources
+
+- [cheat.sh]
+
+[cheat.sh]: cheat.sh/useradd

knowledge base/userdel.md

@@ -0,0 +1,22 @@
+# Useradd
+
+Delete a user account and its related files.
+
+## TL;DR
+
+```shell
+# Remove a user.
+sudo userdel username
+
+# Remove a user in other root directory.
+sudo userdel --root path/to/other/root username
+
+# Remove a user along with the home directory and mail spool.
+sudo userdel --remove username
+```
+
+## Sources
+
+- [cheat.sh]
+
+[cheat.sh]: cheat.sh/userdel

knowledge base/usermod.md

@@ -3,6 +3,36 @@
 ## TL;DR
 
 ```shell
-# Add users to a group.
-sudo usermod --append --groups boinc user
+# Change a user's primary group.
+sudo usermod -g docker bob
+
+# Add/remove a user to/from supplementary groups.
+sudo usermod -aG wheel carly
+sudo usermod --append --groups kvm,video,audio alice
+sudo usermod -rG sudo,admin eve
+
+# Change a user's login name
+sudo usermod --login to-stephen from-micha
+
+# Change a user's ID.
+sudo usermod --uid 1001 hugo
+
+# Change a user's shell.
+sudo usermod --shell /usr/bin/zsh rick
+
+# Change a user's password.
+sudo usermod -p encryptedPassword john
+
+# Lock/unlock a user.
+sudo usermod -L damian
+sudo usermod -U luke
+
+# Change a user's home directory.
+sudo usermod --move-home --home path/to/new_home lonny
 ```
+
+## Sources
+
+- [cheat.sh]
+
+[cheat.sh]: cheat.sh/usermod