#!/bin/sh
# A simple script with a function...
add_a_user()
{
USER=$1
PASSWORD=$2
shift; shift;
# Having shifted twice, the rest is now comments ...
COMMENTS=$@
echo "Adding user $USER ..."
echo useradd -c "$COMMENTS" $USER
echo passwd $USER $PASSWORD
echo "Added user $USER ($COMMENTS) with pass $PASSWORD"
}
###
# Main body of script starts here
###
echo "Start of script..."
add_a_user bob letmein Bob Holness the presenter
add_a_user fred badpassword Fred Durst the singer
add_a_user bilko worsepassword Sgt. Bilko the role model
echo "End of script..."
Linux add a new user called rakhi
Type the command as follows:
useradd rakhi
Set a password for rakhi:
passwd rakhi
Without password user account will be in locked status. To unlock the account, you need to use above passwd
command. Use passwd command to assign a password and set password aging guidelines.
This is an example of how to create a new user using useradd command in Slackware Linux:
root@hitam:~# useradd -g users -d /home/karim -s /bin/bash -c temporary -e
2006-06-30 -m
karim root@hitam:~#
Here are the meaning of command options used in the example above:
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-g (user initial group) - users
-d (user's home directory when login) - /home/karim
-s (user's shell) - /bin/bash
-c (comment) - Temporary
-e (account expired date) - 2009-11-30
-m (create user's home directory)
karim (username of the new account)
All user's information can be found in /etc/passwd file. We can view the file with vi /etc/passwd command.
useradd - Adding a new user
Options:
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-d home directory
-s starting program (shell)
-p password
-g (primary group assigned to the users)
-G (Other groups the user belongs to)
-m (Create the user's home directory
Example: To add a new user with
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a primary group of users
a second group mgmt
starting shell /bin/bash
password of xxxx
home directory of roger
create home directory
a login name of roger
useradd -gusers -Gmgmt -s/bin/shell -pxxxx -d/home/roger -m roger
usermod - Modifying existing user
Options:
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-d home directory
-s starting program (shell)
-p password
-g (primary group assigned to the users)
-G (Other groups the user belongs to)
Example: To add the group 'others' to the user roger
usermod -Gothers roger
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userdel - Deleting a user
Options:
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-r (remove home directory)
Example: To remove the user 'roger' and his home directory
userdel -r roger
passwd - User's Password
Options:
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user's name (Only required if you are root and want to change another user's password)
Example: To change the password for the account you are currently logged in as...
passwd
Enter existing password
Enter new password
Enter new password again (to validate)
Example: To change the password for the user 'roger' (only you are logged in as root)...
passwd roger
Enter existing password (can be either roger's password or root's password)
Enter new password
Enter new password again (to validate)
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Where user and group information stored
User names and primary groups are stored in /etc/passwd. This file can be directly edited using the 'vi' editor,
although this is not recommended. Format of the file is...
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User (name normally all lower case)
Password (encrypted - only contains the letter 'x')
User ID (a unique number of each user)
Primary Group ID
Comment (Normally the person's full name)
Home directory (normally /home/<user name>
Default shell (normally /bin/bash)
Each field is separated by a colon.
Passwords for each user are stored in /etc/shadow. This file should only be changed using the passwd
command.
The useradd Command
The useradd command is used on Linux and other Unix-like operating systems both to add new users (also
referred to as accounts), inclusive of their user names, passwords and other data, and to update default new
user information. The adduser command is identical to useradd, because it is merely a symbolic link to it.
useradd's basic syntax is
useradd [option(s)] username
By default, useradd can only be used by the root (i.e., omnipotent administrative) account. On home computers
and other computers over which the user has complete control, the root account can be accessed by logging in
as root or, preferably, by using the su (i.e., substitute user) command.
The useradd binary (i.e., the ready-to-run program file) is typically located in the /usr/sbin directory, which
contains non-vital system utilities that are used after booting (i.e., starting the system). If this directory is not in
the root user's PATH (i.e., the directories in which the system searches for commands issued by the root user),
an error message such as bash: useradd: command not found will be displayed. In such case, the command
should be typed using its full path (i.e., the full hierarchy of directories from it to the root directory), which
would be /usr/sbin/useradd.
To add a new user to the system, all that is necessary is to follow the useradd or adduser command by that
user's user name. This name is the login name, that is, the name that the user uses when logging into the
system. Only one name can be added with each use of the command, and the name must be unique (i.e.,
different from every other user name already on the system). Thus, for example, to add a new user with a user
name joseph to the system, all that is necessary is to type the following and press the Enter key:
/usr/sbin/useradd joseph
Adding a new user automatically adds an entry to the /etc/passwd file, which is used to store data about users.
Each entry in this file consists of a single line containing a set of seven colon-separated fields, for example,
joseph:x:504:504:Joseph:/home/joseph:/bin/bash
The fields are the user's login name, password (or just the letter x or an asterisk in the likely event that shadow
passwords are used), UID (user identification number), GID (group identification number), comment
(optional), user's home directory and default shell (usually bash on Linux). On a system with shadow
passwords enabled, the actual passwords are encrypted and stored in a separate file which is only accessible to
the root account.
/etc/passwd can be edited by the root user with the use of any text editor, such as vi or gedit, and it can be
viewed by any user by using one of these editors or by employing a command such as cat, i.e.,
cat /etc/passwd
adduser's flexibility is enhanced by the availability of a number of options. Among the more commonly used is
-c, which allows a comment, such as the user's real name and phone number, to be added to /etc/passwd. The
comment can be written as a single string (i.e., a sequence of characters without any intervening spaces), or it
can be multiple strings enclosed in quotes. For example, the following would add a user named joe and would
insert that user's full name, Joe Smith, into the comment field:
useradd -c "Joe Smith" joe
By default the home directory of each user (i.e., the directory that contains a user's personal files and that a
user is first in after logging in) will reside in the /home directory and will have the same name as the user.
Thus, for example, the default home directory for the new user joe would be /home/joe. However, this behavior
can be overriden by using the -d option followed by the full path for the desired new home directory (which
need not be in /home). For example, the following would create a new user named jim with a home directory
/home/james:
useradd -d /home/james jim
The -e option is used to set the date, in YYYY-MM-DD format, on which the new account will automatically
expire. This is useful for creating temporary accounts and for dealing with the tendency of busy system
administrators to forget to delete them, which can become a security risk.
The -f option is used to specify 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. The default value is -1, which
disables this feature.
The name or number of the new user's initial login group can be specified by placing it after the -g option. The
group name must already exist, and a group number must refer to an already existing group. The default group
number is 1 or whatever is specified in the file /etc/default/useradd.
The -G option is used to provide a list of additional groups into which the user is also included. Each group
name or number is separated from the next by a comma, with no intervening spaces. The groups are subject to
the same restrictions as the group specified with the -g option.
The -m option, which does not accept any arguments (i.e., input data), creates the user's home directory;
however, it is not necessary to use it on Red Hat and other systems on which such directory is created
automatically. The -k option is used together with -m to specify an alternative to the default /etc/skel directory
as the source of the initial content (i.e., directories and files) for the new user's home directory. For example,
the following would add the contents of a directory named /dir_1 to /home/jane, which would be the default
home directory of a new user jane:
useradd -m -k /dir_1 jane
The -M option is used to create a new user without creating any home directory for that user. When such a user
logs into a system that has just booted up, its login directory will likely be the root directory; when such a user
logs into a system using the su command, its login directory will be the current directory of the previous user.
On Red Hat systems a new group having the same name as the user being added to the system will be created
by default. The -n option is used to prevent such group from being created. The -o option allows creation of a
user with a non-unique UID.
The -p option is used to specify an encrypted password that has been created by the crypt command. It is not
used to specify the actual password, as this could be a security risk (because such password would be retained
in the history file).
The -r option is used to create accounts for administrative use that have some, but not all, root privileges. Such
accounts have a UID lower than the value of UID_MIN defined in /etc/login.defs (typically 500 and above for
ordinary users) and have a password that does not expire. By default, no home directories are created.
New users are automatically assigned the default login shell, which is bash on Linux unless it has been
changed systemwide. However, any new user can be assigned any other shell as their default by using the -s
option followed by the name of the desired shell.
The -D option is used to view and change the default values for adding users. The following will display the
default settings, which include the initial group, location of the home directory, when the password becomes
inactive, when the account expires, the default shell, and name of the directory that contains the directories
and/or files that are added automatically to the new home directory:
useradd -D
To change any of the default settings for new users, -D is followed by -g, -b, -s, -f and/or -e, which are, in turn,
followed by an appropriate argument. These secondary options are the same as their counterparts described
above, with the exception of -b, which stands for base and is followed by the full path of the directory in which
new home directories are to be created. Thus, for example, to cause the home directory for new users to be
located in a directory called /home/users, the following would be used:
useradd -Db /home/users
Any directory that is specified as the container for new users' home directories need not exist at the time it is
specified with -Db. But it must exist when new users are subsequently created. This can, of course, be easily
accomplished using the mkdir command, which for the above example would be
mkdir /home/users
As an alternative to using the useradd command, users can also be added and their data changed by directly
editing /etc/passwd. However, this is more risky because of the possibility of accidental damage to the file. If a
critical system file such as /etc/passwd is to be edited directly, it is, of course, wise to first make a backup copy
of it.
After adding a new user, the system administrator uses the passwd command to assign that user a password.
User accounts can be removed, preferably, with the userdel command but also by deleting the appropriate line
from /etc/passwd.
-c comment
The new user's password file comment field.
-d home_dir
The new user will be created using home_dir as the value for the user's login directory. The default
is to append the login name to default_home and use that as the login directory name.
-e expire_date
The date on which the user account will be disabled. The date is specified in the format YYYY-MMDD.
-f inactive_days
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.
The default value is -1.
-g initial_group
The group name or number of the user's initial login group. The group name must exist. A group
number must refer to an already existing group. The default group number is 1 or whatever is
specified in /etc/default/useradd.
-G group,[...]
A list of supplementary groups which the user is also a member of. Each group is separated from
the next by a comma, with no intervening whitespace. The groups are subject to the same
restrictions as the group given with the -g option. The default is for the user to belong only to the
initial group.
-m
The user's home directory will be created if it does not exist. The files contained in skeleton_dir
will be copied to the home directory if the -k option is used, otherwise the files contained in
/etc/skel will be used instead. Any directories contained in skeleton_dir or /etc/skel will be created
in the user's home directory as well. The -k option is only valid in conjunction with the -m option.
The default is to not create the directory and to not copy any files.
-M
The user home directory will not be created, even if the system wide settings from /etc/login.defs
is to create home dirs.
-n
A group having the same name as the user being added to the system will be created by default.
This option will turn off this Red Hat Linux specific behavior.
-o
Allow create user with duplicate (non-unique) UID.
-p passwd
The encrypted password, as returned by crypt(3). The default is to disable the account.
-r
This flag is used to create a system account. That is, a user with a UID lower than the value of
UID_MIN defined in /etc/login.defs and whose password does not expire. Note that useradd will
not create a home directory for such an user, regardless of the default setting in /etc/login.defs.
You have to specify -m option if you want a home directory for a system account to be created.
This is an option added by Red Hat.
-s shell
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.
-u uid
The numerical value of the user's ID. This value must be unique, unless the -o option is used. The
value must be non-negative. The default is to use the smallest ID value greater than 99 and greater
than every other user. Values between 0 and 99 are typically reserved for system accounts.
Changing the default values
When invoked with the -D option, useradd will either display the current default values, or update the
default values from the command line. The valid options are
-b default_home
The initial path prefix for a new user's home directory. The user's name will be affixed to the end
of default_home to create the new directory name if the -d option is not used when creating a new
account.
-e default_expire_date
The date on which the user account is disabled.
-f default_inactive
The number of days after a password has expired before the account will be disabled.
-g default_group
The group name or ID for a new user's initial group. The named group must exist, and a numerical
group ID must have an existing entry .
-s default_shell
The name of the new user's login shell. The named program will be used for all future new user
accounts.
If no options are specified, useradd displays the current default values.