Bdtyktl

Just press Ctrl+Alt+T on your keyboard to open Terminal. When it opens, run the command(s) below:

cat /etc/passwd

OR

less /etc/passwd

more /etc/passwd

You can also use awk:^awk

awk -F':' '{ print $1}' /etc/passwd

The easiest way to get this kind of information is getent - see manpage for the getent command . While that command gives the same output as cat /etc/passwd it is useful to remember because it will give you lists of several elements in the OS.

To get a list of all users you type (as users are listed in /etc/passwd)

getent passwd

To add a user newuser to the system you would type

sudo adduser newuser

to create a user that has all default settings applied.

Bonus: To add any user (for instance anyuser) to a group (for instance cdrom) type

sudo adduser anyuser cdrom

You delete a user (for instance obsolete) with

sudo deluser obsolete

If you want to delete his home directory/mails as well you type

sudo deluser --remove-home obsolete

And

sudo deluser --remove-all-files obsolete

will remove the user and all files owned by this user on the whole system.

You can use compgen built-in too:

compgen -u

Will lists all users.

This should get, under most normal situations, all normal (non-system, not weird, etc) users:

awk -F'[/:]' '{if ($3 >= 1000 && $3 != 65534) print $1}' /etc/passwd

This works by:

• reading in from /etc/passwd
  


• using : as a delimiter


• if the third field (the User ID number) is larger than 1000 and not 65534, the first field (the username of the user) is printed.

This is because on many linux systems, usernames above 1000 are reserved for unprivileged (you could say normal) users. Some info on this here:

A user ID (UID) is a unique positive integer assigned by a Unix-like
operating system to each user. Each user is identified to the system
by its UID, and user names are generally used only as an interface for
humans.

UIDs are stored, along with their corresponding user names and other
user-specific information, in the /etc/passwd file...

The third field contains the UID, and the fourth field contains the
group ID (GID), which by default is equal to the UID for all ordinary
users.

In the Linux kernels 2.4 and above, UIDs are unsigned 32-bit integers
that can represent values from zero to 4,294,967,296. However, it is
advisable to use values only up to 65,534 in order to maintain
compatibility with systems using older kernels or filesystems that can
only accommodate 16-bit UIDs.

The UID of 0 has a special role: it is always the root account (i.e.,
the omnipotent administrative user). Although the user name can be
changed on this account and additional accounts can be created with
the same UID, neither action is wise from a security point of view.

The UID 65534 is commonly reserved for nobody, a user with no system
privileges, as opposed to an ordinary (i.e., non-privileged) user.
This UID is often used for individuals accessing the system remotely
via FTP (file transfer protocol) or HTTP (hypertext transfer
protocol).

UIDs 1 through 99 are traditionally reserved for special system users
(sometimes called pseudo-users), such as wheel, daemon, lp, operator,
news, mail, etc. These users are administrators who do not need total
root powers, but who perform some administrative tasks and thus need
more privileges than those given to ordinary users.

Some Linux distributions (i.e., versions) begin UIDs for
non-privileged users at 100. Others, such as Red Hat, begin them at
500, and still others, such Debian, start them at 1000. Because of the
differences among distributions, manual intervention can be necessary
if multiple distributions are used in a network in an organization.

Also, it can be convenient to reserve a block of UIDs for local users,
such as 1000 through 9999, and another block for remote users (i.e.,
users elsewhere on the network), such as 10000 to 65534. The important
thing is to decide on a scheme and adhere to it.

Among the advantages of this practice of reserving blocks of numbers
for particular types of users is that it makes it more convenient to
search through system logs for suspicious user activity.

Contrary to popular belief, it is not necessary that each entry in the
UID field be unique. However, non-unique UIDs can cause security
problems, and thus UIDs should be kept unique across the entire
organization. Likewise, recycling of UIDs from former users should be
avoided for as long as possible.

list of all users who can login (no system users like: bin,deamon,mail,sys, etc.)

awk -F':' '$2 ~ "$" {print $1}' /etc/shadow

add new user

sudo adduser new_username

or

sudo useradd new_username

delete/remove username

sudo userdel username

If you want to delete the home directory (default the directory /home/username)

sudo deluser --remove-home username

or

sudo rm -r /path/to/user_home_dir

If you want to delete all files from the system from this user (not only is the home diretory)

sudo deluser --remove-all-files

Ok here is a trick that will help you sort this. The terminal has auto completion if you type user and hit Tab key twice it will list all the commands that exist with user as the first 4 chars.

user (tab tab)

gives me as possible options
useradd userdel usermod users users-admin

if you want to know more about a command google it or type man
man useradd
gives
useradd - create a new user or update default new user information
...
...

to list users you should go with what Mitch said.

Hope that helps I love tab completion in bash saves me from remembering things.

To find out the users which have home-directories in the /home-folder on the machine, run the following commands

cd /home

ls 

You can then see the users who have authorization to log into the server. If we want to look into the files of any users, you must be the root user.