I need a command to list all users as well as commands to add, delete and modify users from terminal - any commands that could help in administrating user accounts easily by terminal.

2

9 Answers

To list

To list all local users you can use:

cut -d: -f1 /etc/passwd

To list all users capable of authenticating (in some way), including non-local, see this reply.

Some more useful user-management commands (also limited to local users):

To add

To add a new user you can use:

sudo adduser new_username

or:

sudo useradd new_username

See also: What is the difference between adduser and useradd?

To remove/delete

To remove/delete a user, first you can use:

sudo userdel username

Then you may want to delete the home directory for the deleted user account :

sudo rm -r /home/username

Please use with caution the above command!

To modify

To modify the username of a user:

usermod -l new_username old_username

To change the password for a user:

sudo passwd username

To change the shell for a user:

sudo chsh username

To change the details for a user (for example real name):

sudo chfn username

To add a user to the sudo group: 

adduser username sudo

or

usermod -aG sudo username

And, of course, see also: man adduser, man useradd, man userdel... and so on.

9

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
3

The easiest way to get this kind of information is getent - see manpage for the getent command Manpage icon. 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.

4

You can use compgen GNU bash built-in too:

compgen -u

Will lists all users.

0

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.

1

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
2

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.

1

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.

2

The first answer recommends:

cut -d: -f1 /etc/passwd

But using this and counting number of users you get:

$ cut -d: -f1 /etc/passwd | wc -l 46

46 users for a laptop computer are a lot!. So use this instead:

$ cat /etc/passwd | grep -vE '(/bin/false|/sbin/nologin|/bin/sync)' | cut -d: -f1 root rick guest-atkb2q guest-u4sf2i guest-rmlbtg guest-mz53vp

To remove guest accounts (who don't have saved files anyway) use:

$ cat /etc/passwd | grep -vE '(/bin/false|/sbin/nologin|/bin/sync|guest-)' | cut -d: -f1 root rick

Some sample users removed from the listing are:

systemd-timesync:x:100:102:systemd Time Synchronization,,,:/run/systemd:/bin/false gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/usr/sbin/nologin sync:x:4:65534:sync:/bin:/bin/sync sync:x:4:65534:sync:/bin:/bin/sync guest-atkb2q:x:999:999:Guest:/tmp/guest-atkb2q:/bin/bash

It turns out most of the users on a single user system are actually programs that have set themselves up as users.