Modify

User Accounts

Account Management

Command	Description
passwd <username>	Change user password (requires root privileges).
useradd <username>	Create a new user account (requires root privileges).
userdel <username>	Delete an existing user account (requires root privileges).
usermod <username>	Modify various user account settings (requires root privileges).
chfn <options> <username>	Changes the user's finger information (real name, office, phone, etc.).
chsh <options> <username>	Changes the user's login shell.
passwd -l <username>	Lock a user account, preventing login (requires root privileges).
passwd -u <username>	Unlock a locked user account (requires root privileges).
usermod -L <username>	Disable a user account (requires root privileges).
usermod -U <username>	Enable a disabled user account (requires root privileges).

Example: sudo useradd -m -d /home/username -s /bin/bash username

-m: Creates the user's home directory as specified by the -d option. If -d is not specified with -m, the home directory is created under the location specified in /etc/default/useradd or the default /home/username. -d /home/username: Specifies the home directory for the new user. -s /bin/bash: Sets the default shell for the user.

Managing Group Membership

usermod -G <group1>,<group2> <username>	Add/Remove user from specific groups (requires root privileges).
groups <username>	Check user's current group memberships.
usermod -aG <groupname> <username>	Adds a user to a group.

Password Policies

chapw	Manage system-wide password policies (requires root privileges).
chage -l <username>	Display password expiration info for user (requires root privileges).
chage <options> <username>	Changes user password expiry info.

Groups

Group Management

groupadd <groupname>	Creates a new group.
groupdel <groupname>	Deletes a group.
groupmod <options> <groupname>	Modifies a group's name or GID (Group ID).
gpasswd <options> <groupname>	Administers the /etc/group and /etc/gshadow files.
usermod -aG <groupname> <username>	Adds a user to a group. -aG appends the user to the supplemental groups.
vigr	Edits the /etc/group file in a safe manner, similar to using vipw.
vigr -s	Edits the /etc/gshadow file in a safe manner, managing secure group account information.

Editing Config Files Directly

While you can use commands like useradd, userdel, usermod, and passwd for user management, direct editing of /etc/passwd and /etc/shadow is sometimes necessary for manual adjustments. It's recommended to use vipw and vipw -s for editing these files to prevent file corruption and maintain system security. Always back up these files before making direct edits.