create and delete user examples in Red Hat and CentOS
In this tutorial we will learn about creating and deleting the user in Red Hat and CentOS.
In this post we will explore the useradd and userdel commands.
Basic command to create user
In Red Hat and CentOS,create a user and set password as per given below command
useradd user-login-name passwd user-login-name
Now, lets see what happen when you simply use the useradd command in Red Hat and CentOS.
Here I am taking an eg. of creating a user called sharad
[root@localhost ~]# cat /etc/issue CentOS release 6.4 (Final) Kernel r on an m [root@localhost ~]# [root@localhost ~]# useradd sharad [root@localhost ~]# [root@localhost ~]# grep sharad /etc/passwd sharad:x:500:500::/home/sharad:/bin/bash [root@localhost ~]# [root@localhost ~]# grep sharad /etc/group sharad:x:500: [root@localhost ~]# [root@localhost ~]# id sharad uid=500(sharad) gid=500(sharad) groups=500(sharad) [root@localhost ~]# [root@localhost ~]# ls -ld /home/sharad/ drwx------ 2 sharad sharad 4096 Jul 17 20:35 /home/sharad/ [root@localhost ~]# [root@localhost ~]# grep sharad /etc/shadow sharad:!!:15903:0:99999:7::: [root@localhost ~]#
When we create a user by using command “useradd sharad”,the following things are happened
Explore default options of useradd command
To find default options of useradd,use the below given command
useradd -D OR cat /etc/default/useradd
See the below reference of output
[root@localhost ~]# useradd -D
GROUP=100
HOME=/home
INACTIVE=-1
EXPIRE=
SHELL=/bin/bash
SKEL=/etc/skel
CREATE_MAIL_SPOOL=yes
[root@localhost ~]#[root@localhost ~]# cat /etc/default/useradd
# useradd defaults file
GROUP=100
HOME=/home
INACTIVE=-1
EXPIRE=
SHELL=/bin/bash
SKEL=/etc/skel
CREATE_MAIL_SPOOL=yes[root@localhost ~]#
useradd -n test
[root@localhost ~]# useradd -n ravi [root@localhost ~]# id ravi uid=501(ravi) gid=100(users) groups=100(users) [root@localhost ~]#
Now here Question comes, Why UID and GID was 500 when we created the first user called sharad.
Answer: It get the value from /etc/login.defs file.
[root@localhost ~]# grep GID_MIN /etc/login.defs GID_MIN 500 [root@localhost ~]# grep UID_MIN /etc/login.defs UID_MIN 500 [root@localhost ~]#
Tip: If you set the value CREATE_HOME no in /etc/login.defs file, the home directory of user will not be created.
See in below reference the newly created user’s home directory and /etc/skel contents are same
[root@localhost ~]# ls -la /etc/skel/ total 20 drwxr-xr-x. 2 root root 4096 May 29 23:17 . drwxr-xr-x. 63 root root 4096 Jul 17 21:17 .. -rw-r--r--. 1 root root 18 Feb 22 03:05 .bash_logout -rw-r--r--. 1 root root 176 Feb 22 03:05 .bash_profile -rw-r--r--. 1 root root 124 Feb 22 03:05 .bashrc [root@localhost ~]# [root@localhost ~]# ls -la /home/sharad/ total 20 drwx------ 2 sharad sharad 4096 Jul 17 21:01 . drwxr-xr-x. 5 root root 4096 Jul 17 21:17 .. -rw-r--r-- 1 sharad sharad 18 Feb 22 03:05 .bash_logout -rw-r--r-- 1 sharad sharad 176 Feb 22 03:05 .bash_profile -rw-r--r-- 1 sharad sharad 124 Feb 22 03:05 .bashrc [root@localhost ~]#
Question: Where is the mail spool directory
Answer: It is mentioned in /etc/login.defs file.
[root@localhost ~]# grep MAIL_DIR /etc/login.defs |grep spool MAIL_DIR /var/spool/mail [root@localhost ~]#
How to change default value of useradd command
You can also change the default value of useradd
Method 1 : By using command line
examples:
For changing default shell use command useradd -D -s /shell/path
[root@localhost ~]# useradd -D -s /bin/sh You have new mail in /var/spool/mail/root [root@localhost ~]# useradd -D GROUP=100 HOME=/home INACTIVE=-1 EXPIRE= SHELL=/bin/sh SKEL=/etc/skel CREATE_MAIL_SPOOL=yes [root@localhost ~]#
For Changing Default Home Directory,use command useradd -D -b /new/home_dir/path
[root@localhost ~]# mkdir /new_home [root@localhost ~]# useradd -D -b /new_home [root@localhost ~]# [root@localhost ~]# useradd -D GROUP=100 HOME=/new_home INACTIVE=-1 EXPIRE= SHELL=/bin/sh SKEL=/etc/skel CREATE_MAIL_SPOOL=yes [root@localhost ~]#
Likewise you can also do other changes.
Method 2: By editing /etc/default/useradd .
vi /etc/default/useradd # useradd defaults file GROUP=100 HOME=/new_home INACTIVE=-1 EXPIRE= SHELL=/bin/sh SKEL=/etc/skel CREATE_MAIL_SPOOL=yes
Using useradd command with many options
(1) Changing login shell at useradd command. Bydefault the login shell is /bin/bash
Use -s with useradd command
[root@localhost ~]# useradd -s /bin/sh testuser [root@localhost ~]# [root@localhost ~]# grep testuser /etc/passwd testuser:x:502:502::/home/testuser:/bin/sh [root@localhost ~]#
(2) Changing default home directory to other path.
Use -d option here, useradd -d /Path/username username
[root@localhost ~]# mkdir /new_home [root@localhost ~]# useradd -d /new_home/joe joe [root@localhost ~]# ls /new_home/ joe [root@localhost ~]# ls /new_home/joe/ [root@localhost ~]# ls -ld /new_home/joe/ drwx------ 2 joe joe 4096 Jul 17 23:04 /new_home/joe/ [root@localhost ~]#
(3) Changing userid , use -u option here
[root@localhost ~]# useradd -u 600 john [root@localhost ~]# id john uid=600(john) gid=600(john) groups=600(john) [root@localhost ~]#
(3) Changing group id with useradd command, use -g option.
Note 1: Group must already exist so that we can use its GID. See below example.
GID of hr group is 601
Note 2: hr group has GID 600 . User tester taken bydefault UID 601 also because there was no user exist with this UID. If exist than it would get the different UID as per increment pattern.
[root@localhost ~]# groupadd hr [root@localhost ~]# [root@localhost ~]# grep hr /etc/group hr:x:601: [root@localhost ~]# useradd -u 550 -g 601 roger [root@localhost ~]# id roger uid=550(roger) gid=601(hr) groups=601(hr) [root@localhost ~]# [root@localhost ~]# useradd -g 601 tester [root@localhost ~]# id tester uid=601(tester) gid=601(hr) groups=601(hr) [root@localhost ~]#
(4) You can use available options in single line. Here I have added -c for GECOS or comment
See below example
[root@localhost ~]# useradd -c "linux system admin" -u 700 -g 601 -s /bin/sh -d /new_home/sharadchhetri sharadchhetri[root@localhost ~]# id sharadchhetri uid=700(sharadchhetri) gid=601(hr) groups=601(hr) [root@localhost ~]# grep sharadchhetri /etc/passwd sharadchhetri:x:700:601:linux system admin:/new_home/sharadchhetri:/bin/sh [root@localhost ~]#
(5) Set password in single line with -p option. But here you have to get encrypt passwd.
useradd -p #$#@encrypted@#$ username
see below example how you will do. Here I will use the password PaaSS2ord
Get encrypted password by using command openssl
[root@localhost ~]# openssl passwd -crypt Password: Verifying - Password: Warning: truncating password to 8 characters gYqytYyfGxwII [root@localhost ~]#
after using openssl command we get the encrypted value of PaaSS2ord as gYqytYyfGxwII
Now use this value with -p option
[root@localhost ~]# useradd -p 'gYqytYyfGxwII' testred
You can check by login user testred using the password PaaSS2ord
Below given are options which you can use with useradd command
[root@localhost ~]# 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
-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
[root@localhost ~]#
Delete User in Red hat and CentOS
(1) To delete the user ,use below given command
userdel username
Note: The above command will not remove user’s home directory and mail spool
(2) Delete user with its home directory and mail spool. Use option -r
userdel -r username
Other options which you can also use
[root@localhost ~]# userdel --help
Usage: userdel [options] LOGIN
Options:
-f, --force force removal of files,
even if not owned by user
-h, --help display this help message and exit
-r, --remove remove home directory and mail spool
-Z, --selinux-user remove SELinux user from SELinux user mapping
[root@localhost ~]#
