useradd - this
cmd is used to add new user to the system
-d specify
home dir
-e expiry
date
-s shell
-G group
-u UID
/etc/login.defs - this file stores all the parameters for
users
passwd [username] - creates a password for the user
usermod
This modifies user's account
-m used with
-d, this moves contents of the current home dir to the new one specified
-U unlocks password
-L locks account
-l changes username (usermod -l new_username
old_username)
chage
This command deals with account expiration
-m sets the
minimum time before a user can change password. Usage: -m 1 (1 day)
-M sets the
maximum time after which password needs to be changed
-d sets the
last day the password was changed (can be used to manipulate account info)
-I sets number of inactive days allowed before
password expires
-E sets
expiration date
-W sets
warndays – warn the user before the password expires
userdel
This cmd is used to delete users from a system.
Options:
-r remove
all the files from home dir and mail spool
-f force
deletion of the account (when the user is logged in)
-h get help
/etc/group - this
file controls the group membership (also /etc/gshadow)
/etc/passwd -
this file contains info on the user's primary group (also /etc/shadow)
newgrp - this cmd
is used for changing current group to a different one
chgrp - this cmd
is used to change the group of a file or dir
First 100 GIDs and UIDs (0-99) are reserved for system use
(generally)
0 UID/GID belongs to root
- always
groupadd
This cmd adds a new group to the system.
Options:
-g specifies
a GID
-r creates a
system group
-f forces
creation
groupmod
This cmd modifies a group.
Options:
-g specify a
new group ID for an existing group
-n specify a
new group name for an existing group
gpasswd
This cmd sets a password for the group
Options:
-a add a user
to the group usage: -a user group
-d delete a
user from the group usage: -d user group
-R configures
a group to not allow the cmd newgrp
-r removes
the password from a group
-A specify
group admin
groupdel
This cmd deletes a group