Group 4

Homeworks/Answer.md

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+# Framgia Training Workshop - Linux Essential 2
+## Homework answer (Group 4)
+
+### Homework 1
+Question: "Why can a normal user change his/her password without root permission?"  
+Answer: When run `ls -l $(which passwd)`, output is:  
+`-rwsr-xr-x 1 root root 54256 Th05 17 06:37 /usr/bin/passwd` -> `755`  
+In permission of `passwd` command has `s` flag in 4th position, this make the command run as owner instead of user run it.  
+So any user run this command, it always run as root user (it's owner).  
+Finally, normal user can run `passwd` command, but root user will update password database.
+
+### Homework 2
+```
+# Apply for shared directory
+# Default owner for new file and directory is creator.
+chgrp framgia /path/to/shared_directory # Change group to framgia
+chmod g+s /path/to/shared_directory # New created file and directory has group is framgia (from command above)
+umask u=rwx,g=rwx,o= # New file will create with permission 660 and directory is 770
+
+```
+
+### Homework 3
+```
+" Display line numbers
+set number
+
+" Set file encodings
+set fileencodings=utf-8,shift-js,sjis
+
+" Disable arrow keys
+noremap <Up> <Nop>
+noremap <Down> <Nop>
+noremap <Left> <Nop>
+noremap <Right> <Nop>
+
+" Replace tab with 4 spaces
+set tabstop=4
+set shiftwidth=4
+set expandtab
+```
+
+Add support for Elixir language  
+Step 1: Clone vim-elixir repo:
+```
+git clone https://github.com/elixir-lang/vim-elixir.git
+```
+Step 2: Install  
+- Step 2.1: With pathogen plugin manager, copy `vim-elixir` folder to ~/.vim/bundle  
+- Step 2.2: Manual install, copy contents of each directory in the respective directories inside ~/.vim
+
+### Homework 4
+Create public-private key file name dev_rsa
+```
+ssh-keygen -N '' -f dev_rsa -t rsa
+```
+- -N '': no passphrase
+- -f dev_rsa: create two file output: dev_rsa for private, dev_rsa.pub for public
+- -t rsa: key type is rsa
+
+Write ssh config file
+File ~/.ssh/config
+```
+Host dev
+    HostName 128.45.53.123
+    Port 2222
+    # Replace with location of private key file
+    IdentityFile ~/.ssh/dev_rsa
+    # Replace with real username on server
+    User username
+```
+
+### Homework 5
+File create_acc.sh
+
+```
+#!/bin/bash
+
+function show_help() {
+  echo "Usage: sudo create_acc.sh {username} {password} {path/to/pubkey_file}"
+  exit 1
+}
+
+if [ "$#" -ne 3 ]; then
+  echo "Number of arguments is invalid!!!"
+  show_help
+fi
+
+if [ ! -f $3 ] || [ ! -r $3 ]; then
+  echo "$3 is invalid file."
+  show_help
+fi
+
+if [ $UID -ne 0 ]; then
+  echo "Please run this script as root or sudo command"
+  show_help
+fi
+
+sudo useradd -m -p $(openssl passwd -1 $2) -g admin $1
+sudo mkdir -p /home/$1/.ssh
+sudo cat $3 >> /home/$1/.ssh/authorized_keys
+sudo chmod 600 /home/$1/.ssh/authorized_keys
+sudo chmod 700 /home/$1/.ssh
+sudo chown -R $1 /home/$1/.ssh
+exit 0
+```