practice Linux - repl.it, Git for Windows, Visual Studio Code, Powershell

• ~ home dir
• $ standard user
• # root user
• period - current directory
• switches: -l = long list / -la = full details (perms, date, user) / -a = all - ls -a
• Linux is case sensitive
• spaces in file name - use backslash \

| - piping - output one cmd/prog and inputs to another

• ls -al | cat > lsout.txt (list files in current dir inside lsout.txt)
• echo Hello World | cat >> newfile.txt - adds message to bottom of newfile.txt

global regular expression print. grep searches files for keywords | grep keyword file.txt

• grep options:
  • grep keyword filename - prints all lines containing the keyword
  • grep '\!$' filename - using regular expression to match lines ending in a !
  • --color=always - highlight matched text in color
  • -c - how many lines matched
  • -n - matches and line number
  • -i - case insensitive grep -ni "keyword" file.txt
  • -v - invert match, find all lines that don't match reg exp
  • -l - only show the filenames of the files that matched
  • -L - shows names of files that don't contain matching lines
  • -r - recursive - search all files in dirs and subdirs
  • -R - ls -R folder-name lists files and folders inside folder-name
  • -o - only print matching part of the line, not whole line
  • -a - search binaries - treat binary data like its text instead of ignoring it
  • -F - don't treat the match string as a regex
  • -E - extended support of meta characs, escapes these special characters by default (use if you want regexps like '.+' to work, otherwise you need to use '.+'
  • grep -A 3 keyword shows 3 lines of context after a match
  • cat auth.log | grep "keyword" | awk '{print $4}' | sort -u > file.txt prints sorted list from column 4 from the auth.log file to file.txt,
  • (avoid egrep and fgrep)
  • grep alternatives - ack, ag, ripgrep - better for searching code

advanced

• regular expressions
• aliases

Enhanced version of vi. 2 modes - insert (enter text) and command (del text, copy/paste and other ops)

View files and perms with 'ls -l'. File perms are in 1st col.

• Example: drwxr-xr-x. 1st charac is the file type. d = dir or '-' for file

  • r = readable means can view file, w = writable means can edit/del file, x = executable means can execute and access file/dir.
  • rwx means full access and a dash means no access given.

• There are 3 sets - user, group, others (UGO).

  • 1st set/1st 4 chars - 'drwx' in this dir, user/owner has full rwx perms.
  • 2nd set/5-7th chars - 'r-x' - this group can read (r) and execute (x) but not write (w).
  • 3rd set/8-10th chars - 'r-x' - all other users can read (r) and execute (x) but not write (w).
  • r = 4 bits, w = 2 bits, x = 1 bit = 4+2+1 = 7 bits / rwx = 777 = full access / 774 = all perms to user and group, read perms to others / 766 = user has rwx, all others and group rw only (4+2=6)

For more info - chmod Command in Linux and commands with examples

• chmod - change perms/mode, root user or file owner only. | chmod 774 file.txt
• UGO (text) method instead of numeric (777)
• References: (u) user, (g) group, (o) others
• Operators: - means removes, + means adds, = means sets/assigns
• Modes: (r) read, (w) write, (x) execute, (a) all

Examples:

1. chmod u-w file.txt (removes w perm for user)
2. chmod u+x, o+x file.txt (user and others can execute to file.txt)
3. chmod ugo=rx file.txt (everyone has rx perms)
4. chmod a=rx file.txt (same as ugo, all users have rx perms)
5. chmod ugo+rwx file.txt (all perms to all users)

Tables from LinkedIn Learning course

• Begin with #!/bin/bash (means it's executable, saved as .sh file by default). / #!/bin/bash -x - debugging (remove later) / place in script, then run file in terminal:

set -x 
(what you want to debug) 
+x

• add scripts to your bin dir - /home/username/bin (exe in the bin only available to you, can't run with sudo) or /usr/local/bin (avail to all users, can run sudo)
• New scripts are NOT executable. chmod 755 bashfile.sh or chmod +x bashfile.sh to make it executable.
• Commands work exactly the same on the command line as they do within a script.
• To run file bash script.sh or ./bashfile in the terminal. (./ = to run script)
• Comments -- single line # your comment -- multi-line

  :'your comment in between single quotes
  next line
  another line'

= - to set variable, $ - call var | myvar="yo world" echo $myvar - outputs 'yo world' when your run script -i = removes case sensitivity / -n = line number

Conditionals

if statements

if [ statement ] 
then 
  echo 'your message' 
  exit
fi

else
  echo 'another message'
fi  

if (( ... ))
then 
  echo "..."
else
  echo "..."
fi

operators

• && = and, -a
• || = or, -o

myVar=(var)

if ["$myVar" -gt 18] && ["$age" -lt 40]
then
  echo "true"
else
  echo "not true"
fi

Can also use:

• ["$myVar" -gt 18 -a "$age" -lt 40]
• [ ... -o ...]
• [..] OR [..]
• [ ... || ... ]
• [ ... ] || [ ... ]

user input

echo "Enter your name:"
read name
echo "Enter your age:"
read age
echo "Hello" $name, "you are" $age "years old"

Read - for user input. Run script, and user inputs name, age. Notes from

read -p "Enter your username: " username
read -sp "Enter your password: " password

echo -e "\nYour username is $username and Password is $password"

• -p prompt a message, displays on screen
• -sp - doesn't display on screen

Resources

• Bash scripting tut
• BASH3 Boilerplate
• Bash Boilerplate

RSA 2048-bit encryption, which is comparative to a 617 digit long password. More secure than passwords.

SSH keys are made up of a private key and a public key. Never share private key. If key is exposed, generate a new ssh key pair.

Can choose to either lock your private key with a passphrase. creating a key pair without a passphrase is more convenient and potentially essential for certain scripts and automation tasks. But it's also less secure. Generate a separate key pair for each service or connection you want to use, adding a passphrase only for critical services.

By default you private key is stored at /Users/myname/.ssh/id_rsa and your public key The private key - id_rsa - should never be shared

Public keys (id_rsa.pub) are meant to be shared or placed on a remote server. It's stored at /Users/myname/.ssh/id_rsa.pub. The private key is stored at /Users/myname/.ssh/id_rsa.

To generate a key - ssh-keygen

~/.ssh/id_rsa ~/.sshid_rsa.pub - public key goes into server "authorized_keys" file

To connect to server - ssh name@ip.address.here or ssh name@server.domainname.com, enter the servers password to authenticate (not local machine)

To add public key and enable pw-less login ssh-copy-id user@host

Create a config file and alias cd .ssh ls to view files, and touch config vi config

Host dev
  HostName <domain or ip>
  Port 22
  User <username>
  IdentityFile ~/.ssh/id_rsa

You can now SSH into the systems with this command ssh dev

SSH Tunneling Access resources on remote server or allow acccess to your local resources to someone else. (Creating a tunnel to ssh to a machine and forward data from one port to another). Need a ssh client (work) and ssh server (home)

Setup public SSH Server Local Port Forwarding - access remote resources that you can't access, internal remote database, RDP ssh -L local_port:remote_address:remote_port username@sshserver Ex. ssh -L 8888:192.168.1.3:8080 44.11.22.33

Remote Port Forwarding - other ppl to have access to local resources they don't have access to, eg. local web server ssh -R remote_port:local_address:local_port username@sshserver Ex. ssh -R 8888:10.0.0.3:8080 44.11.22.33 The ssh server config /etc/ssh/sshd_config should have a property GatewayPorts yes

Github Go to Settings, then ssh and gpg keys, add new, add your public key (ls to view files, cat id_rsa.pub), copy full key and paste in gh. Cloning with ssh - git clone <git@github.com link>

Resources

• ssh tutorial
• ssh cheat sheet
• ssh tunneling explained
• ssh tunneling tutorial