Linux Commands – useradd

Hello Everyone

Welcome to CloudAffaire and this is Debjeet.

In the last blog post, we have discussed groupmod command in Linux which is used to modify an existing group attribute.

https://cloudaffaire.com/linux-commands-groupmod/

In this blog post, we will discuss useradd command in Linux. useradd command is used to create a new user in Linux. When invoked without the -D option, the useradd command creates a new user account using the values specified on the command line plus the default values from the system. Depending on command line options, the useradd command will update system files and may also create the new user’s home directory and copy initial files. User name can be up to 32 characters long and you need root or sudo privileges to create a user.

User Configurations:

CREATE_HOME (boolean): Indicate if a home directory should be created by default for new users. This setting does not apply to system users, and can be overridden on the command line.
GID_MAX (number), GID_MIN (number): Range of group IDs used for the creation of regular groups by useradd, groupadd, or newusers. The default value for GID_MIN (resp. GID_MAX) is 1000 (resp. 60000).
MAIL_DIR (string): The mail spool directory. This is needed to manipulate the mailbox when its corresponding user account is modified or deleted. If not specified, a compile-time default is used.
MAIL_FILE (string): Defines the location of the users mail spool files relatively to their home directory. The MAIL_DIR and MAIL_FILE variables are used by useradd, usermod, and userdel to create, move, or delete the user’s mail spool. If MAIL_CHECK_ENAB is set to yes, they are also used to define the MAIL environment variable.
MAX_MEMBERS_PER_GROUP (number): Maximum members per group entry. When the maximum is reached, a new group entry (line) is started in /etc/group (with the same name, same password, and same GID). The default value is 0, meaning that there are no limits in the number of members in a group.
PASS_MAX_DAYS (number): The maximum number of days a password may be used. If the password is older than this, a password change will be forced. If not specified, -1 will be assumed (which disables the restriction).
PASS_MIN_DAYS (number): The minimum number of days allowed between password changes. Any password changes attempted sooner than this will be rejected. If not specified, -1 will be assumed (which disables the restriction).
PASS_WARN_AGE (number): The number of days warning given before a password expires. A zero means warning is given only upon the day of expiration, a negative value means no warning is given. If not specified, no warning will be provided.
SYS_GID_MAX (number), SYS_GID_MIN (number): Range of group IDs used for the creation of system groups by useradd, groupadd, or newusers. The default value for SYS_GID_MIN (resp. SYS_GID_MAX) is 101 (resp. GID_MIN-1).
SYS_UID_MAX (number), SYS_UID_MIN (number): Range of user IDs used for the creation of system users by useradd or newusers. The default value for SYS_UID_MIN (resp. SYS_UID_MAX) is 101 (resp. UID_MIN-1).
UID_MAX (number), UID_MIN (number): Range of user IDs used for the creation of regular users by useradd or newusers. The default value for UID_MIN (resp. UID_MAX) is 1000 (resp. 60000).
UMASK (number): The file mode creation mask is initialized to this value. If not specified, the mask will be initialized to 022.
USERGROUPS_ENAB (boolean): Enable setting of the umask group bits to be the same as owner bits (examples: 022 -> 002, 077 -> 007) for non-root users, if the uid is the same as gid, and username is the same as the primary group name.

User Files:

/etc/passwd: User account information.
/etc/shadow: Secure user account information.
/etc/group: Group account information.
/etc/gshadow: Secure group account information.
/etc/default/useradd: Default values for account creation.
/etc/skel/: Directory containing default files.
/etc/login.defs: Shadow password suite configuration.

Linux Commands – useradd:

You can use useradd command to create a new user.

##############################
## Linux Commands | useradd ##
##############################
## Prerequisites: One Unix/Linux/POSIX-compliant operating system with bash shell

##--------
## useradd
##--------
## useradd [options] LOGIN
## useradd -D [options]

sudo useradd myuser                  ## create a user

## User account information.
sudo grep "myuser" /etc/passwd       ## returns myuser:x:1001:1001::/home/myuser:/bin/bash

## Secure user account information.
sudo grep "myuser" /etc/shadow       ## returns myuser:!!:18408:0:99999:7:::

## Group account information.
sudo grep "myuser" /etc/group        ## returns myuser:x:1001:

## Secure group account information.
sudo grep "myuser" /etc/gshadow      ## returns myuser:!::

## Default values for account creation.
sudo cat /etc/default/useradd        ## returns default values

## Directory containing default files.
sudo ls /etc/skel/                   ## returns default files if configured

## user configuration.
sudo cat /etc/login.defs             ## returns user and group config

sudo userdel -rf myuser              ## delete the user

##############################

## Linux Commands | useradd ##

##############################

## Prerequisites: One Unix/Linux/POSIX-compliant operating system with bash shell

##--------

## useradd

##--------

## useradd [options] LOGIN

## useradd -D [options]

sudo useradd myuser ## create a user

## User account information.

sudo grep "myuser" /etc/passwd ## returns myuser:x:1001:1001::/home/myuser:/bin/bash

## Secure user account information.

sudo grep "myuser" /etc/shadow ## returns myuser:!!:18408:0:99999:7:::

## Group account information.

sudo grep "myuser" /etc/group ## returns myuser:x:1001:

## Secure group account information.

sudo grep "myuser" /etc/gshadow ## returns myuser:!::

## Default values for account creation.

sudo cat /etc/default/useradd ## returns default values

## Directory containing default files.

sudo ls /etc/skel/ ## returns default files if configured

## user configuration.

sudo cat /etc/login.defs ## returns user and group config

sudo userdel -rf myuser ## delete the user

You can use useradd -p or –password PASSWORD option to set the user login credentials. The default is to disable the password.

Note: This option is not recommended because the password (or encrypted password) will be visible by users listing the processes. Instead set the user password using passwd command.

## useradd -p or --password PASSWORD option options

sudo useradd --password "mypwd" myuser  ## create myuser with password mypwd
sudo grep "myuser" /etc/shadow          ## returns myuser:mypwd:18408:0:99999:7:::

su - myuser                             ## try to login using myuser
                                        ## will not work as the password provided with
                                        ## --password needs to be encrypted, but we provided in plain 
                                        ## text, you can use mkpasswd to get the encrypted version

sudo passwd myuser                      ## enter a password as per your system password policy
                                        ## generally defined in /etc/pam.d/
su - myuser                             ## try to login using myuser new password
pwd                                     ## by default user home directory is created in /home/myuser
exit                                    ## exit myuser

sudo userdel -rf myuser                 ## delete the user

## useradd -p or --password PASSWORD option options

sudo useradd --password "mypwd" myuser ## create myuser with password mypwd

sudo grep "myuser" /etc/shadow ## returns myuser:mypwd:18408:0:99999:7:::

su - myuser ## try to login using myuser

## will not work as the password provided with

## --password needs to be encrypted, but we provided in plain

## text, you can use mkpasswd to get the encrypted version

sudo passwd myuser ## enter a password as per your system password policy

## generally defined in /etc/pam.d/

su - myuser ## try to login using myuser new password

pwd ## by default user home directory is created in /home/myuser

exit ## exit myuser

sudo userdel -rf myuser ## delete the user

You can use useradd -d or –home-dir HOME_DIR options to create a custom home directory (HOME_DIR) for the user. By default, the user’s home directory is created as /home/user_name.

## useradd -d or --home-dir HOME_DIR options 

sudo useradd -d /tmp/myuser myuser      ## create a user with custom home dir
sudo passwd myuser                      ## set the password
su - myuser                             ## login as myuser
echo $HOME                              ## returns /tmp/myuser
exit

sudo userdel -rf myuser                 ## delete the user

## useradd -d or --home-dir HOME_DIR options

sudo useradd -d /tmp/myuser myuser ## create a user with custom home dir

sudo passwd myuser ## set the password

su - myuser ## login as myuser

echo $HOME ## returns /tmp/myuser

exit

sudo userdel -rf myuser ## delete the user

You can use useradd -b or –base-dir BASE_DIR options to create a custom base directory for the user if -d HOME_DIR is not specified. BASE_DIR is concatenated with the account name to define the home directory. The BASE_DIR must exist otherwise the home directory cannot be created. If this option is not specified, useradd will use the base directory specified by the HOME variable in /etc/default/useradd, or /home by default.

## useradd -b or --base-dir BASE_DIR options

mkdir /tmp/mybasedir                    ## create a directory
sudo useradd -b /tmp/mybasedir myuser   ## create a user with custom base dir
sudo passwd myuser                      ## set the password
su - myuser                             ## login as myuser
echo $HOME                              ## returns /tmp/mybasedir/myuser
exit

sudo userdel -rf myuser                 ## delete the user

## useradd -b or --base-dir BASE_DIR options

mkdir /tmp/mybasedir ## create a directory

sudo useradd -b /tmp/mybasedir myuser ## create a user with custom base dir

sudo passwd myuser ## set the password

su - myuser ## login as myuser

echo $HOME ## returns /tmp/mybasedir/myuser

exit

sudo userdel -rf myuser ## delete the user

You can use useradd -c or –comment COMMENT options to add a short description of the user.

## useradd -c or --comment COMMENT options

sudo useradd -c "cloudaffaire" myuser   ## create a user with short description

sudo grep "myuser" /etc/passwd          ## returns myuser:x:1001:1001:cloudaffaire:/home/myuser:/bin/bash

sudo userdel -rf myuser                 ## delete the user

## useradd -c or --comment COMMENT options

sudo useradd -c "cloudaffaire" myuser ## create a user with short description

sudo grep "myuser" /etc/passwd ## returns myuser:x:1001:1001:cloudaffaire:/home/myuser:/bin/bash

sudo userdel -rf myuser ## delete the user

You can use useradd -e or –expiredate EXPIRE_DATE options to define the date on which the user account will be disabled. The date is specified in the format YYYY-MM-DD. If not specified, useradd will use the default expiry date specified by the EXPIRE variable in /etc/default/useradd, or an empty string (no expiry) by default.

## useradd -e or --expiredate EXPIRE_DATE options

sudo useradd -e 2020-12-31 myuser       ## create a user with expiry date

sudo chage -l myuser                    ## returns Account expires : Dec 31, 2020

sudo userdel -rf myuser                 ## delete the user

## useradd -e or --expiredate EXPIRE_DATE options

sudo useradd -e 2020-12-31 myuser ## create a user with expiry date

sudo chage -l myuser ## returns Account expires : Dec 31, 2020

sudo userdel -rf myuser ## delete the user

You can use useradd -f or –inactive INACTIVE options to define the number of days after a password expires until the account is permanently disabled. A value of 0 disables the account as soon as the password has expired, and a value of -1 disables the feature. If not specified, useradd will use the default inactivity period specified by the INACTIVE variable in /etc/default/useradd, or -1 by default.

## useradd -f or --inactive INACTIVE options 

sudo useradd --inactive 30 myuser       ## create a user with password inactive days

sudo passwd myuser                      ## set user password

sudo passwd -x 90 myuser                ## set password expiry date

sudo chage -l myuser                    ## returns
                                        ## Password expires : Aug 25, 2020
                                        ## Password inactive : Sep 24, 2020

sudo userdel -rf myuser                 ## delete the user

## useradd -f or --inactive INACTIVE options

sudo useradd --inactive 30 myuser ## create a user with password inactive days

sudo passwd myuser ## set user password

sudo passwd -x 90 myuser ## set password expiry date

sudo chage -l myuser ## returns

## Password expires : Aug 25, 2020

## Password inactive : Sep 24, 2020

sudo userdel -rf myuser ## delete the user

You can use useradd -s or –shell SHELL options to define the name of the user’s login shell. The default is to leave this field blank, which causes the system to select the default login shell specified by the SHELL variable in /etc/default/useradd, or an empty string by default.

## useradd -s or --shell SHELL options

sudo grep "SHELL" /etc/default/useradd  ## returns SHELL=/bin/bash

sudo useradd -s /bin/sh myuser          ## make /bin/sh as default shell

sudo grep "myuser" /etc/passwd          ## myuser:x:1001:1001::/home/myuser:/bin/sh

sudo userdel -rf myuser                 ## delete the user

## useradd -s or --shell SHELL options

sudo grep "SHELL" /etc/default/useradd ## returns SHELL=/bin/bash

sudo useradd -s /bin/sh myuser ## make /bin/sh as default shell

sudo grep "myuser" /etc/passwd ## myuser:x:1001:1001::/home/myuser:/bin/sh

sudo userdel -rf myuser ## delete the user

You can use useradd -r or –system options to create a system account. There is no difference between a system user and a normal user, only system users will be created with no aging information in /etc/shadow, and their numeric identifiers are chosen in the SYS_UID_MIN-SYS_UID_MAX range, defined in /etc/login.defs, instead of UID_MIN-UID_MAX (and their GID counterparts for the creation of groups). Also, for system user useradd will not create a home directory, regardless of the default setting in /etc/login.defs (CREATE_HOME). You have to specify the -m options if you want a home directory for a system account to be created.

## useradd -r or --system options 

sudo useradd -r myuser                  ## create a system user

sudo grep "myuser" /etc/passwd          ## myuser:x:996:994::/home/myuser:/bin/bash

sudo ls /home/myuser                    ## ls: cannot access /home/myuser: No such file or directory             

sudo grep "myuser" /etc/shadow          ## myuser:!!:18409::::::

sudo userdel -rf myuser                 ## delete the user

## useradd -r or --system options

sudo useradd -r myuser ## create a system user

sudo grep "myuser" /etc/passwd ## myuser:x:996:994::/home/myuser:/bin/bash

sudo ls /home/myuser ## ls: cannot access /home/myuser: No such file or directory

sudo grep "myuser" /etc/shadow ## myuser:!!:18409::::::

sudo userdel -rf myuser ## delete the user

You can use useradd -m or –create-home options to create the user’s home directory if it does not exist. The files and directories contained in the skeleton directory (which can be defined with the -k option) will be copied to the home directory. By default, if this option is not specified and CREATE_HOME is not enabled, no home directories are created.

## useradd -m or --create-home options

sudo useradd -r myuser                  ## create a system user (home dir not created by deafult)

sudo ls -l /home | grep myuser          ## home directory is not created

sudo userdel -rf myuser                 ## delete the user

sudo useradd -m -r myuser               ## create a system user (with -m, home dir is created)

sudo ls -l /home | grep myuser          ## drwx------ 2 myuser   myuser    62 May 27 06:09 myuser

sudo userdel -rf myuser                 ## delete the user

## useradd -m or --create-home options

sudo useradd -r myuser ## create a system user (home dir not created by deafult)

sudo ls -l /home | grep myuser ## home directory is not created

sudo userdel -rf myuser ## delete the user

sudo useradd -m -r myuser ## create a system user (with -m, home dir is created)

sudo ls -l /home | grep myuser ## drwx------ 2 myuser myuser 62 May 27 06:09 myuser

sudo userdel -rf myuser ## delete the user

You can use useradd -k or –skel SKEL_DIR options to copy the content of skeleton directory to user’s home directory. This option is only valid if the -m (or –create-home) option is specified. If this option is not set, the skeleton directory is defined by the SKEL variable in /etc/default/useradd or, by default, /etc/skel.

## useradd -k or --skel SKEL_DIR options

sudo grep SKEL /etc/default/useradd     ## SKEL=/etc/skel

sudo mkdir -p /tmp/myskel/myfile        ## create a directory

sudo useradd -m -k /tmp/myskel myuser   ## create the user

sudo ls -l /home/myuser                 ## drwxr-xr-x 2 myuser myuser 6 May 27 06:42 myfile

sudo userdel -rf myuser                 ## delete the user

## useradd -k or --skel SKEL_DIR options

sudo grep SKEL /etc/default/useradd ## SKEL=/etc/skel

sudo mkdir -p /tmp/myskel/myfile ## create a directory

sudo useradd -m -k /tmp/myskel myuser ## create the user

sudo ls -l /home/myuser ## drwxr-xr-x 2 myuser myuser 6 May 27 06:42 myfile

sudo userdel -rf myuser ## delete the user

You can use useradd -M or –no-create-home options to disable home directory creation even if the system wide setting from /etc/login.defs (CREATE_HOME) is set to yes.

## useradd -M or --no-create-home options

sudo grep CREATE_HOME /etc/login.defs   ## CREATE_HOME     yes

sudo useradd myuser                     ## create a user
sudo ls -l /home | grep myuser          ## drwx------ 2 myuser   myuser    62 May 27 06:09 myuser
sudo userdel -rf myuser                 ## delete the user

sudo useradd -M myuser                  ## create a user
sudo ls -l /home | grep myuser          ## home directory not created
sudo userdel -rf myuser                 ## delete the user

## useradd -M or --no-create-home options

sudo grep CREATE_HOME /etc/login.defs ## CREATE_HOME yes

sudo useradd myuser ## create a user

sudo ls -l /home | grep myuser ## drwx------ 2 myuser myuser 62 May 27 06:09 myuser

sudo userdel -rf myuser ## delete the user

sudo useradd -M myuser ## create a user

sudo ls -l /home | grep myuser ## home directory not created

sudo userdel -rf myuser ## delete the user

You can use useradd -u or –uid UID options to provide custom user id. This value must be unique and non-negative, unless the -o option is used. The default is to use the smallest ID value greater than or equal to UID_MIN and greater than every other user.

## useradd -u or --uid UID options

sudo grep "UID*" /etc/login.defs        ## get UID config

sudo useradd myuser                     ## create a user
sudo grep "myuser" /etc/passwd          ## myuser:x:1001:1001::/home/myuser:/bin/bash
sudo userdel -rf myuser                 ## delete the user

sudo useradd -u 2001 myuser             ## create a user
sudo grep "myuser" /etc/passwd          ## myuser:x:2001:2001::/home/myuser:/bin/bash
sudo userdel -rf myuser                 ## delete the user

## useradd -u or --uid UID options

sudo grep "UID*" /etc/login.defs ## get UID config

sudo useradd myuser ## create a user

sudo grep "myuser" /etc/passwd ## myuser:x:1001:1001::/home/myuser:/bin/bash

sudo userdel -rf myuser ## delete the user

sudo useradd -u 2001 myuser ## create a user

sudo grep "myuser" /etc/passwd ## myuser:x:2001:2001::/home/myuser:/bin/bash

sudo userdel -rf myuser ## delete the user

You can use useradd -o or –non-unique options to allow the creation of a user account with a duplicate (non-unique) UID. This option is only valid in combination with the -u option.

## useradd -o or --non-unique options 

sudo useradd -u 2001 myuser1            ## create myuser1 with UID 2001

sudo useradd -u 2001 myuser2            ## try to create myuser2 with UID 2001
                                        ## useradd: UID 2001 is not unique

sudo useradd -o -u 2001 myuser2         ## now try with -o option   

sudo grep "myuser*" /etc/passwd         ## returns
                                        ## myuser1:x:2001:2001::/home/myuser1:/bin/bash
                                        ## myuser2:x:2001:2002::/home/myuser2:/bin/bash

sudo userdel -rf myuser1                ## delete the users
sudo userdel -rf myuser2

## useradd -o or --non-unique options

sudo useradd -u 2001 myuser1 ## create myuser1 with UID 2001

sudo useradd -u 2001 myuser2 ## try to create myuser2 with UID 2001

## useradd: UID 2001 is not unique

sudo useradd -o -u 2001 myuser2 ## now try with -o option

sudo grep "myuser*" /etc/passwd ## returns

## myuser1:x:2001:2001::/home/myuser1:/bin/bash

## myuser2:x:2001:2002::/home/myuser2:/bin/bash

sudo userdel -rf myuser1 ## delete the users

sudo userdel -rf myuser2

You can use useradd -K or –key KEY=VALUE options to overrides /etc/login.defs defaults (UID_MIN, UID_MAX, UMASK, PASS_MAX_DAYS and others).

## useradd -K or --key KEY=VALUE options

sudo cat /etc/login.defs

sudo useradd -r myuser                  ## create a system user
sudo grep "myuser" /etc/passwd          ## myuser:x:996:994::/home/myuser:/bin/bash
sudo userdel -rf myuser                 ## delete the user

## create a system user with -K option
sudo useradd -r -K SYS_UID_MIN=2000 -K SYS_UID_MAX=4000 myuser    
sudo grep "myuser" /etc/passwd          ## myuser:x:4000:994::/home/myuser:/bin/bash
sudo userdel -rf myuser                 ## delete the user

## useradd -K or --key KEY=VALUE options

sudo cat /etc/login.defs

sudo useradd -r myuser ## create a system user

sudo grep "myuser" /etc/passwd ## myuser:x:996:994::/home/myuser:/bin/bash

sudo userdel -rf myuser ## delete the user

## create a system user with -K option

sudo useradd -r -K SYS_UID_MIN=2000 -K SYS_UID_MAX=4000 myuser

sudo grep "myuser" /etc/passwd ## myuser:x:4000:994::/home/myuser:/bin/bash

sudo userdel -rf myuser ## delete the user

You can use useradd -U or –user-group options to create a group with the same name as the user, and add the user to this group. The default behavior (if the -g, -N, and -U options are not specified) is defined by the USERGROUPS_ENAB variable in /etc/login.defs.

## useradd -U or --user-group options 

sudo grep USERGROUPS_ENAB /etc/login.defs   ## returns USERGROUPS_ENAB yes

sudo useradd -U myuser                  ## create a user with group name same as user name

sudo grep "myuser" /etc/group           ## myuser:x:1001:

id -g -n myuser                         ## myuser is the primary group of myuser

sudo userdel -rf myuser                 ## delete the user

## useradd -U or --user-group options

sudo grep USERGROUPS_ENAB /etc/login.defs ## returns USERGROUPS_ENAB yes

sudo useradd -U myuser ## create a user with group name same as user name

sudo grep "myuser" /etc/group ## myuser:x:1001:

id -g -n myuser ## myuser is the primary group of myuser

sudo userdel -rf myuser ## delete the user

You can use useradd -g or –gid GROUP options to add the user to an existing group. -g options accept both group name or number of the user’s initial login group. If not specified, the behavior of useradd will depend on the USERGROUPS_ENAB variable in /etc/login.defs. If this variable is set to yes (or -U/–user-group is specified on the command line), a group will be created for the user, with the same name as her loginname. If the variable is set to no (or -N/–no-user-group is specified on the command line), useradd will set the primary group of the new user to the value specified by the GROUP variable in /etc/default/useradd, or 100 by default.

## useradd -g or --gid GROUP options

sudo groupadd mygroup                   ## create a new group
sudo grep "mygroup" /etc/group          ## returns mygroup:x:1001:

sudo useradd -g mygroup myuser          ## create a user and add to a group
id -g -n myuser                         ## mygroup is the primary group of myuser

sudo userdel -rf myuser                 ## delete the user
sudo groupdel mygroup                   ## delete the group mygroup

## useradd -g or --gid GROUP options

sudo groupadd mygroup ## create a new group

sudo grep "mygroup" /etc/group ## returns mygroup:x:1001:

sudo useradd -g mygroup myuser ## create a user and add to a group

id -g -n myuser ## mygroup is the primary group of myuser

sudo userdel -rf myuser ## delete the user

sudo groupdel mygroup ## delete the group mygroup

You can use useradd -G or –groups GROUP1[,GROUP2,…[,GROUPN]]] options to add the user to multiple secondary group during user creation. All the groups must pre-exist and needs to be separated from the next by a comma, with no intervening whitespace.

## useradd -G or --groups GROUP1[,GROUP2,...[,GROUPN]]] options

sudo groupadd mygroup1                  ## create some groups
sudo groupadd mygroup2
sudo groupadd mygroup3

## create user, adding it to multiple groups
sudo useradd -g mygroup1 -G mygroup2,mygroup3 myuser

id -g -n myuser                         ## Primary group: mygroup1 

id -G -n myuser                         ## returns mygroup1 mygroup2 mygroup3 

sudo userdel -rf myuser                 ## delete the user
sudo groupdel mygroup1                  ## delete the groups
sudo groupdel mygroup2
sudo groupdel mygroup3

## useradd -G or --groups GROUP1[,GROUP2,...[,GROUPN]]] options

sudo groupadd mygroup1 ## create some groups

sudo groupadd mygroup2

sudo groupadd mygroup3

## create user, adding it to multiple groups

sudo useradd -g mygroup1 -G mygroup2,mygroup3 myuser

id -g -n myuser ## Primary group: mygroup1

id -G -n myuser ## returns mygroup1 mygroup2 mygroup3

sudo userdel -rf myuser ## delete the user

sudo groupdel mygroup1 ## delete the groups

sudo groupdel mygroup2

sudo groupdel mygroup3

You can use useradd -N or –no-user-group options to not create a group with the same name as the user, but add the user to the group specified by the -g option or by the GROUP variable in /etc/default/useradd. The default behavior (if the -g, -N, and -U options are not specified) is defined by the USERGROUPS_ENAB variable in /etc/login.defs.

## useradd -N or --no-user-group options

sudo groupadd mygroup                   ## create a group
sudo useradd -G mygroup myuser          ## create a user
id -g -n myuser                         ## returns myuser
id -G -n myuser                         ## returns myuser mygroup
sudo userdel -rf myuser                 ## delete the user

sudo useradd -N -G mygroup myuser       ## create a user with -N option
id -g -n myuser                         ## returns users
id -G -n myuser                         ## returns users mygroup

sudo userdel -rf myuser                 ## delete the user
sudo groupdel mygroup                   ## delete the group

## useradd -N or --no-user-group options

sudo groupadd mygroup ## create a group

sudo useradd -G mygroup myuser ## create a user

id -g -n myuser ## returns myuser

id -G -n myuser ## returns myuser mygroup

sudo userdel -rf myuser ## delete the user

sudo useradd -N -G mygroup myuser ## create a user with -N option

id -g -n myuser ## returns users

id -G -n myuser ## returns users mygroup

sudo userdel -rf myuser ## delete the user

sudo groupdel mygroup ## delete the group

You can use useradd -D or –defaults options to update the default user configurations defined in /etc/default/useradd file. You can change below default configurations using -D option

-b, –base-dir BASE_DIR: The path prefix for a new user’s home directory.
-e, –expiredate EXPIRE_DATE: The date on which the user account is disabled.
-f, –inactive INACTIVE: The number of days after a password has expired before the account will be disabled.
-g, –gid GROUP: The group name or ID for a new user’s initial group.
-s, –shell SHELL: The name of a new user’s login shell.

## useradd -D or --defaults options  

sudo useradd -D                         ## get current default configs

sudo useradd -D -s /bin/sh              ## change SHELL from /bin/bash to /bin/sh

sudo useradd -D                         ## get current default configs

sudo useradd -D -s /bin/bash            ## change back SHELL from /bin/sh to /bin/bash

## useradd -D or --defaults options

sudo useradd -D ## get current default configs

sudo useradd -D -s /bin/sh ## change SHELL from /bin/bash to /bin/sh

sudo useradd -D ## get current default configs

sudo useradd -D -s /bin/bash ## change back SHELL from /bin/sh to /bin/bash

Hope you have enjoyed this article. In the next blog post, we will discuss passwd command in Linux.

Linux Commands – useradd

User Configurations:

User Files:

Linux Commands – useradd:

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