Add a user named Mike
First, change to root and use the command
useradd -m -s /bin/bash Mike
-m create user's home directory;
-s appoints user's shell type, such as sh, csh, tcsh or bash;
useradd -m -s /bin/bash -G sudo Mike
-G add Mike to another group(s);
passwd Mike
to set user's password, if you don't do this step, the user can't login the system;
If you want the new user Mike could use "sudo", you need to modify the file "/etc/sudoers", or use below command for Ubuntu
gpasswd -a Mike sudo
for CentOS
gpasswd -a Mike wheel
then modify /etc/sudoers, uncomment #%wheel ALL=(ALL) ALL, means wheel group could oprate any machine by any user do any thing;
Delete the user Mike
Use the command
userdel -r Mike
to delete the user and the home directory;
or
userdel Mike
just delete user Mike but keep the home directory;
Modify user's name User to Mike
usermod -l Mike -m -d /home/Mike User
-l modify user name User to Mike, -d appoint to user directory /home/Mike and the directory /home/Mike should exist; -m rename the old directory to the new one, if the old directory doesn't exist, then create it.
Add/delete user to/from a second group
gpasswd -a user group2
Add user to a second group
gpasswd -d user group2
delete user from a second group
groups operations
- create group
groupadd grp
add a grp group
- rename group
groupmod -n grp_new grp_old
rename group name grp_old to grp_new
- delete group
groupdel grp
delete group grp
- list group
- view current user belongs group(s);
groups
- list user belongs group(s)
groups user
- list all groups
cat /etc/group
some system has no /etc/group file, use another way
cat /etc/passwd |awk -F [:] ‘{print $4}’ |sort|uniq | getent group |awk -F [:] ‘{print $1}’
note that getent command could find group infomation by GID;
user operations
add user
useradd --help
Usage: useradd [options] LOGIN
Options:
-b, --base-dir BASE_DIR base directory for the home directory of the
new account
-c, --comment COMMENT GECOS field of the new account
-d, --home-dir HOME_DIR home directory of the new account
-D, --defaults print or change default useradd configuration
-e, --expiredate EXPIRE_DATE expiration date of the new account
-f, --inactive INACTIVE password inactivity period of the new account
-g, --gid GROUP name or ID of the primary group of the new
account
-G, --groups GROUPS list of supplementary groups of the new
account
-h, --help display this help message and exit
-k, --skel SKEL_DIR use this alternative skeleton directory
-K, --key KEY=VALUE override /etc/login.defs defaults
-l, --no-log-init do not add the user to the lastlog and
faillog databases
-m, --create-home create the user's home directory
-M, --no-create-home do not create the user's home directory
-N, --no-user-group do not create a group with the same name as
the user
-o, --non-unique allow to create users with duplicate
(non-unique) UID
-p, --password PASSWORD encrypted password of the new account
-r, --system create a system account
-R, --root CHROOT_DIR directory to chroot into
-s, --shell SHELL login shell of the new account
-u, --uid UID user ID of the new account
-U, --user-group create a group with the same name as the user
-Z, --selinux-user SEUSER use a specific SEUSER for the SELinux user mapping
passwd user
add a new user, must set user's passwd;
Modify user's infomation
usermod
Usage: usermod [options] LOGIN
Options:
-c, --comment COMMENT new value of the GECOS field
-d, --home HOME_DIR new home directory for the user account
-e, --expiredate EXPIRE_DATE set account expiration date to EXPIRE_DATE
-f, --inactive INACTIVE set password inactive after expiration
to INACTIVE
-g, --gid GROUP force use GROUP as new primary group
-G, --groups GROUPS new list of supplementary GROUPS
-a, --append append the user to the supplemental GROUPS
mentioned by the -G option without removing
him/her from other groups
-h, --help display this help message and exit
-l, --login NEW_LOGIN new value of the login name
-L, --lock lock the user account
-m, --move-home move contents of the home directory to the
new location (use only with -d)
-o, --non-unique allow using duplicate (non-unique) UID
-p, --password PASSWORD use encrypted password for the new password
-R, --root CHROOT_DIR directory to chroot into
-s, --shell SHELL new login shell for the user account
-u, --uid UID new UID for the user account
-U, --unlock unlock the user account
-v, --add-subuids FIRST-LAST add range of subordinate uids
-V, --del-subuids FIRST-LAST remvoe range of subordinate uids
-w, --add-subgids FIRST-LAST add range of subordinate gids
-W, --del-subgids FIRST-LAST remvoe range of subordinate gids
-Z, --selinux-user SEUSER new SELinux user mapping for the user account
usermod -d /home/user1 -G grp user
modify user's login dir to /home/user1, then join in grp group, should use -G;
gpasswd -a user group2
add user to group group2
gpasswd -d user group2
delete user from group group2
delete user
userdel -r user
delete user test
list users
list current login users
w
who
list current user's name
whoami
view user's information
finger apacheuser
id apacheuser
view login log
last #view users who login succeed;
lastb #view users who login failed;
list all users
cut -d : -f 1 /etc/passwd
cat /etc/passwd | awk -F \: ‘{print $1}’
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