Add and format a number of Linux commands

src/linux.md

@@ -1,129 +1,142 @@
 # Linux
 
-SSH into a server with Raspberry Pi's default user.
-```
+## SSH
+Type `exit` to exit out of a SSH session.
+
+```bash
+# SSH into a server with Raspberry Pi's default user.
 ssh pi@<ip_address>
-...
-exit
-```
 
-List all files in a directory, with full paths, into a text file.
-```
-find wwwroot -type f > files.txt
-```
+# SSH into a server as a particular user.
+ssh <user_name>@<ip_address>
 
-Print working directory (current directory).
-```
-pwd
-```
-
-By itself, move to the current user's home directory. Tilde is short for home directory.
-```
-cd
-cd ~
-```
-
-Output current user's name.
-```
+# Output current user's name.
 whoami
 ```
 
-Make a new directory
-```
-mkdir name
-mkdir name1 name2 name3
-```
-
-Make a new directory and sub-directory/ies
-```
-mkdir -p path/to/directory
-```
-
-Look at a file or multiple files.
-```
-cat file.txt
-cat file1.txt file2.txt
-cat file?.txt
-cat file*
-```
-
-Write to a file.
-```
-echo "Some text" > file.txt
-echo "Some more text" >> file.txt
-```
-
-File viewer.
-```
-less file.txt
-# q to quit
-```
-
-Move file(s)/directories to a directory
-```
-mv file.txt dir1
-mv file1.txt file2.txt dir1
-mv file1.txt file2.txt new-dir dir1
-```
-
-Rename a file.
-```
-mv file.txt new-name.txt
-```
-
-Copy a file
-```
-cp path/to/file.txt .
-cp file.txt copy-file.txt
-```
-
-Remove/delete a file.
-```
-rm file.txt
-```
-
-Remove/delete an empty directory.
-```
-rmdir path/to/directory
-```
-
-Remove/delete a directory, even if it has files.
-```
-rmdir -r path/to/directory
-```
-
-Count number of files and folders in home directory.
-```
-ls ~ | wc -l
-```
-
-View disk space.
-```bash
-df -h
-```
-
-Package management:
-```bash
-sudo dpkg --audit
-sudo dpkg --get-selections
-```
-
-View OS information.
-```bash
-cat /etc/os-release
-```
-
-Reboot
+## System management
 ```bash
+# Reboot
 sudo reboot
 sudo shutdown -r now
 # Reboot in 5 minutes.
 sudo shutdown -r 5
+
+# Shutdown
+sudo poweroff
 ```
 
-Shutdown
+## File system
+
+### Information
 ```bash
-sudo poweroff
+# View disk space.
+df
+df -h
+
+# Count number of files and folders in home directory.
+ls ~ | wc -l
+```
+
+### Navigation
+```bash
+# Print working directory (current directory).
+pwd
+
+# By itself, move to the current user's home directory. Tilde is short for home directory.
+cd
+cd ~
+```
+
+### Modification
+```bash
+# Make a new directory.
+mkdir name
+mkdir name1 name2 name3
+
+# Make a new directory and sub-directory/ies.
+mkdir -p path/to/directory
+
+# Move file(s)/directories to an existing directory.
+mv file.txt dir1
+mv file1.txt file2.txt dir1
+mv file1.txt file2.txt new-dir dir1
+
+# Rename a file.
+mv file.txt new-name.txt
+
+# Copy a file
+cp path/to/file.txt .
+cp file.txt copy-file.txt
+
+# Remove/delete a file.
+rm file.txt
+
+# Remove/delete an empty directory.
+rmdir path/to/directory
+
+# Remove/delete a directory, even if it has files.
+rmdir -r path/to/directory
+```
+
+### File viewing and creation
+```bash
+# Look at a file or multiple files.
+cat file.txt
+cat file1.txt file2.txt
+cat file?.txt
+cat file*
+
+# Write to a file.
+echo "Some text" > file.txt
+echo "Some more text" >> file.txt
+
+# File viewer. Press q to quit.
+less file.txt
+
+# List all files in a directory, with full paths, into a text file.
+find wwwroot -type f > files.txt
+```
+
+### Hidden content
+```bash
+# Make a hidden directory.
+mkdir .dir1
+
+# Make a hidden file.
+mkdir .hide.txt
+
+# List all hidden files/folders.
+ls -a
+```
+
+## System information
+```bash
+# View OS information.
+cat /etc/os-release
+
+# View system information on Ubuntu, which is displayed on SSH login:
+landscape-sysinfo
+
+# System monitoring.
+top
+# Prettier version of top.
+htop
+
+# Memory usage.
+free
+free -h
+# Show in MBs.
+free -m
+```
+
+## Package management
+```bash
+# List installed packages.
+dpkg --list
+
+sudo dpkg --audit
+sudo dpkg --get-selections
 ```
 
 ## Permissions
@@ -138,9 +151,7 @@ getent group
 
 # List all groups a user (username) is in.
 groups username
-```
 
-```bash
 # Add write access to group.
 chmod g+w file-or-directory
 
@@ -156,19 +167,3 @@ chmod ugo+rwx file-or-directory
 # Only read to all.
 chmod a=r file-or-directory
 ```
-
-## Hidden
-Make a hidden directory.
-```
-mkdir .dir1
-```
-
-Make a hidden file.
-```
-mkdir .hide.txt
-```
-
-List all hidden files/folders.
-```
-ls -a
-```