🧑‍💻 Linux User & Group Management Cheat Sheet

🔍 Viewing User Info from `/etc/shadow`

cat /etc/shadow

Example entry:

radin:$y$j9T$gxn.Bgl/nVnzPEeWn0Hrz.$CEeQGtg1TlZ/jwu9Zsz2kkIq3dBtbhJ/bzhVT7cJ1.9:20270:0:99999:7:::

Field	Description	Example
👤 Username	User’s login name	`radin`
🔒 Password Hash	Encrypted password	`$y$j9T$gxn.Bgl/nVnzPEeWn0Hrz.$CEeQGtg1TlZ/...`
🗓️ Last Changed	Days since Jan 1, 1970 when password changed	`20270` (which is 20270 + 1970 = year)
⏳ Min Age	Minimum days between password changes	`0`
⏰ Max Age	Maximum days before password must be changed	`99999`
⚠️ Warning Period	Days before expiration user is warned	`7`

cat /etc/group

Example:

radin:x:1000:
sudo:x:27:radin

Field	Description	Example
👥 Group Name	Name of the group	`radin`, `sudo`
🔑 Password	Password (usually `x` means none)	`x`
🆔 GID	Group ID	`1000`, `27`
👤 Users	Users in the group (comma-separated)	`radin`

groups <username>

id <username>

Example output:

uid=1000(radin) gid=1000(radin) groups=1000(radin),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),100(users),114(lpadmin)

Command	Description
`useradd <username>`	Add user without home directory
`useradd -m <username>`	Add user with home directory
`useradd -s /bin/bash -m <username>`	Add user with bash shell & home directory
`useradd -G group1,root -m <username>`	Add user with home and extra groups

passwd <username>

Command	Description
`userdel <username>`	Delete user
`userdel -r <username>`	Delete user and their home directory
`userdel -f <username>`	Force delete user

Command	Description
`usermod [options] username`	Modify user with various options
`usermod -l <newusername> <oldusername>`	Rename user
`usermod -d <dir> -m <username>`	Change user home directory and move files
`usermod -G <groups> <username>`	Set new groups (replaces old groups)
`usermod -aG <group> <username>`	Add user to a supplementary group
`usermod -s <shell> <username>`	Change user login shell