Overview

• Note the linux commands I need to use.

Users Management

ACTIVATE The Added Group Without Login

# When you added user to group via "usermod" command, it doesn't prompt immediately.
# You cna relogin the useranme or type "newgrp" command to enable it.
$ newgrp [-] [group]

ADD The User & Password

# -d: -d [home_dir], The new user will be created using HOME_DIR as the value for the user's login directory
# -G: -G GROUP1[,GROUP2,...[,GROUPN]]], A list of supplementary groups, separated by a comma, and no intervening whitespace
# -m: Create the user's home directory if it does not exist
# -p: -p [password], The password should be encrypted, the default is to disable the password
# -s, -s /bin/bash, The name of the user's login shell, set it as /bin/bash is recommended
$ sudo useradd -m -s /bin/bash -d [home_dir] -G [group] [username]
$ sudo passwd [username]

# SET user account and password in ONE line
$ useradd -p $(openssl passwd -1 password) -m -s /bin/bash -d [home_dir] -G [group] username

BATCH Comment & Uncomment

# Batch Comment
# Step1. Vim file
# Step2. Ctrl+v, enter "VISUAL BLOCK" mode
# Step3. Up & Down to scroll group
# Step4. Shift+i
# Step5. Type "#" in the first line
# Step6. Type Esc
# Step7. Type :wq  Save & Quit

# Batch Uncomment
# Step1. Vim file
# Step2. Ctrl+v, enter "VISUAL BLOCK" mode
# Step3. Up & Down to scroll group
# Step4. Type d
# Step5. Type :wq  Save & Quit

CHANGE The Mode Of Files And Directories

# It uses byte to identify the authority of each level, User, Group and Others

$ chmod [-cfvR] [--version] mode file...
e.g. 
# Everyone can read, write and execute file
$ chmod 777 file

CHANGE The Owner Of The File

$ chown -R [username]:[groupname] [filename]

CHANGE The User’s HOME_DIR

# The usermod command supports "-d" flag to change the HOME_DIR path.
$ sudo usermod -d /new/home/path [username]

CHANGE The User’s Info

# The usermod command supports "-c" flag to change the user info.
$ sudo usermod -c [New User Info] [USERNAME]

CHANGE The User’s Name

# The usermod command supports "-l" flag to change the username.
$ sudo usermod -l [new_username] [old_username]

CHANGE The Group’s Name

# The groupmod command supports "-n" flag to change the group name.
$ sudo groupmod  -n [NEW_GROUPNAME] [OLD_GROUPNAME]

CHANGE The Hostname / Computer Nmae

# The hostnamectl command supports "set-hostname" flag to change the hostname
# The commandline info doesn't changes util re-login, but it changes immediately on hostname and hostnamectl command
# The [new hostname] allows "-","a-z","0-9" only, "_"(underscore) is not-allowed
$ hostnamectl set-hostname [new hostname].

CHANGE / SETUP The User’s Home Directory

$ usermod -d [home directory] [username]
$ usermod -d /home/jenkins jenkins

# Verify $Home directory has changed
$ echo $HOME

DELETE The User’s Account

# [NOTICE] BECAREFUL! This command will DELETE USER
$ sudo deluser [username]

FIND The Process Name Via PID

$ sudo ps -fp [PID]

FIND The Current Location

• It shows the current directory path

$ pwd
/home/rpiauto

FIND The OS Info

• To identify which OS platform in your docker container

$ cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=22.04
DISTRIB_CODENAME=jammy
DISTRIB_DESCRIPTION="Ubuntu 22.04.4 LTS"

or

$ cat /etc/os-release
PRETTY_NAME="Ubuntu 22.04.4 LTS"
NAME="Ubuntu"
VERSION_ID="22.04"
VERSION="22.04.4 LTS (Jammy Jellyfish)"
VERSION_CODENAME=jammy
ID=ubuntu
ID_LIKE=debian
HOME_URL="https://www.ubuntu.com/"
SUPPORT_URL="https://help.ubuntu.com/"
BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
UBUNTU_CODENAME=jammy

INTRODUCE The Common Groups

# Introduce the common groups, so you will know which groups you need to add
# dialout, the dialout group controls ttyUSB devices, you need get the permission to logging console and access

LIST Users

$ cat /etc/passwd

LIST Groups And Belonged Users

$ cat /etc/group

LIST The Groups That The User Has Joined

$ groups [username]
[username] : [list of groups]

REMOVE The User From The Group

$ sudo deluser [username] [group]

SET Number In Vim Editor Permanently

# Show number list in Vim editor

# Create the .vimrc file if not exists
$ touch ~/.vimrc

# Edit the .vimrc file
$ vim ~/.vimrc

# Add your desired settings, such as enabling line numbers:
$ set number

# Save & Exit
# You will see the number list shows on the left in the opened file

Users Management

• How to Create Users in Linux (useradd Command)
  • https://linuxize.com/post/how-to-create-users-in-linux-using-the-useradd-command/
• How to Remove or Delete a User in Linux
  • https://www.hivelocity.net/kb/remove-or-delete-user-linux/?utm_term=&utm_campaign=test-p-max-dedicated&utm_source=adwords&utm_medium=ppc&hsa_acc=4622126547&hsa_cam=21074304377&hsa_grp=&hsa_ad=&hsa_src=x&hsa_tgt=&hsa_kw=&hsa_mt=&hsa_net=adwords&hsa_ver=3&gad_source=1&gclid=Cj0KCQjwsaqzBhDdARIsAK2gqnfp_YtIaaA5NC_T-4FS0D4VYIGPgMT1Un5u6k6dL7rM4-hEsoVfK6saAuhcEALw_wcB
• useradd command in Linux with examples
  • https://linuxconfig.org/useradd
• How To Change The HOME_DIR Of User
  • https://blog.csdn.net/linux_tcpdump/article/details/131648681
• How To Change The USERNAME In Linux
  • https://www.naukri.com/code360/library/how-to-change-username-in-linux
• How To Rename a Group in Linux
  • https://www.geeksforgeeks.org/how-to-rename-a-group-in-linux/
• Understanding /etc/passwd file fields
  • https://www.cyberciti.biz/faq/understanding-etcpasswd-file-format/
• Change User Info on the Command Line
  • https://unix.stackexchange.com/questions/149665/change-user-info-on-the-command-line
• When trying to change username, terminal tells me user is currently used by process
  • https://unix.stackexchange.com/questions/233614/when-trying-to-change-username-terminal-tells-me-user-is-currently-used-by-proc
• 5 Ways to Change Hostname on Linux - wikiHow
  • https://www.wikihow.com/Change-Hostname-on-Linux#:~:text=Run%20the%20command%20sudo%20nmcli%20general%20hostname%20newhostname%20.&text=Your%20new%20hostname%20will%20be,hostnamed%20to%20restart%20systemd%2Dhostnamed.
• How to Change Hostname on Ubuntu
  • https://phoenixnap.com/kb/ubuntu-20-04-change-hostname
• Linux “chmod” Commands
  • https://www.runoob.com/linux/linux-comm-chmod.html