Step 6: Linux administration

Discussion page

Understanding the directory tree structure

Introduction to the directory tree structure on Linux

Useful commands

• mkdir # Makes a directory
• ls # Lists contents of a directory
• tree # Shows a tree of directories
• sudo # Fixes everything, all my problems have been solved this way
• rm -rf # Removes a folder -r = recursively and -f = force
• df # Disk Free, shows information about current disk usage
• free # Shows stats on RAM and swap memory

Useful flags

• -h # Human readable, converts units to be easier to read

Symlinks are super useful to link files to new directories so one file can appear in many places. A few examples I have are my .vimrc configs/plugin which I store in a git repository that is stored elsewhere, another is on my webserver I have a folder for my encryption certificates which allows me to have a folder to automate renewals whilst distributing those out to the folders they need to be in

Linux Directories

• /boot directory stores data related to booting up the system
• /cdrom is where attached CDs to the system are accessed from, similar to /media and /mnt
• /dev location of device files. A device file is an interface to a device driver
• /etc is where configuration files are kept
• /home where users keep files related to their account (documents, photos, videos)
• /lib Libraries are a collection of resources used by the computer, also considered modules
• /lost+found found in each partition, used for things like system recover
• /opt custom applications that are not essential to the operating system
• /proc process folder. An instance of an application
• /root the home folder for the root user
• /run mountpoint for tempfs filesystem in the computer's memory. Temporary data about processes are kept in there. Processes have the extension pid
• /bin this is where binaries are kept
• /sbin binaries for the system
• /snap flatpak is better 😏
• /srv Where service folders are kept, not so commonly used anymore, /opt is getting more popular
• /sys mounted on a virtual file system
• /tmp where temporary files are kept on disk. Sometimes emptied on OS restart
• /usr where programs and libraries are stored
• /var dynamic data and libraries used on the operating system and computer
  • /var/spool for example is a folder related to mail services

Beginner Linux administration

Linux commands

• wget downloads files to local drive
• curl similar to wget but has more options on how to download objects. Can run basic syntax on them too such as for extracting archives
• vim text editor, heavily relies on keyboard only navigation
• grep similar to cat or bat, but lets you filter contents of a file (useful for CSV files, for example). Doesn't support highlighting but when piped with cat it can!
• diff show the differences between two files
• useradd adds a new user to the system
  • -m can be used to create a home directory for them too
• passwd allows you to set a password for a user
• history shows history of commands entered in to the terminal. I personally use fish and autocomplete because I find it quicker

Linux inode

• Two files that store data about a file
  • Inode - Metadata about the file
  • File table - file names and inode number
• ls -i on an object will return its inode number:

 monotiller@laptop  ~  ls -i .zshrc
36685457 .zshrc

• stat lets you view the inode data

 monotiller@laptop  ~  stat .zshrc                                                    
16777234 36685457 -rw-r--r-- 1 monotiller staff 0 4510 "Apr  7 20:47:35 2022" "Apr  7 16:21:28 2022" "Apr  7 16:21:28 2022" "Feb 25 14:26:49 2022" 4096 16 0 .zshrc

Linux Terminal file descriptors and redirections

• find finds file with names, can also use wildcards
• ps shows currently running processes

Linux Terminal – user groups permissions

Video repeated from previous lesson

Linux Terminal permissions – (/chmod)

• chmod allows you to change the permissions set on a folder or directory
• Add -r to introduce these changes to child directories and files
• Numbers are used to determine the state of permissions:
  • Read = 4
  • Write = 2
  • Execute = 1
  • No permissions = 0
• You can use simple addition to combine permissions:
  • Read and write = 6
  • RWX = 7