# chage -E 2005-12-31 user1
set deadline for user password [man]
# groupadd [group]
create a new group [man]
# groupdel [group]
delete a group [man]
# groupmod -n moon sun
rename a group from moon to sun [man]
# grpck
check correct syntax and file format of '/etc/group' and groups existence [man]
# newgrp - [group]
log into a new group to change default group of newly created files [man]
# passwd
change password [man]
# passwd user1
change a user password (only by root) [man]
# pwck
check correct syntax and file format of '/etc/passwd' and users existence [man]
# useradd -c "User Linux" -g admin -d /home/user1 -s /bin/bash user1
create a new user "user1" belongs "admin" group [man]
# useradd user1
create a new user [man]
# userdel -r user1
delete a user ( '-r' eliminates home directory) [man]
# usermod -c "User FTP" -g system -d /ftp/user1 -s /bin/nologin user1
change user attributes as description, group and other [man]