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how to add, delete, modify users?[script] 본문

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how to add, delete, modify users?[script]

MJSon 2017. 4. 9. 21:29






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I need a command to list all users in terminal. And how to add, delete, modify users from terminal.

That could help in administrating your accounts easily by terminal.

community wiki

1  
sed answer sed 's/:.*//' /etc/passwd – Avinash Raj Jul 21 '16 at 13:02
up vote 585 down vote accepted

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: http://askubuntu.com/a/414561/571941

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

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 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 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

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

answered Jan 24 '14 at 20:23

Radu Rădeanu
87k26193276
8  
Radu forgot to mention sudo chfn <username> which changes user details (for example real name). I tried to add this as a comment, but I got error telling me that I must have +50 reputation to do so. – Mikaela Jan 29 '14 at 7:26
1  
I think that it should be underlined that the correct answer to the linked question is askubuntu.com/a/381646/16395 --- otherwise you have to take into account the GID/UID Ubuntu policies by hand. The accepted answer is not so clear. – Rmano May 21 '14 at 18:02
    
sudo userdel DOMAIN\\johndoe gives me the error: "userdel: cannot remove entry 'DOMAIN\johndoe' from /etc/passwd -- I looked in /etc/passwd and they're not even in there, likely because it's a "domain" account? – 00fruX Aug 7 '14 at 19:44
1  
@00fruX Yeah... If you're using a centralised user database you're going to need to deal with it directly. – Oli♦ Aug 8 '14 at 8:32
    
What if cat returns access denied /etc/passwd, although this happens on root account ? – Overmind Jul 17 '15 at 12:11

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
answered Jan 24 '14 at 19:28

Mitch♦
69.5k13145196
    
how to add users by command ? – nux Jan 24 '14 at 19:31
    
You can use useradd command. – Mitch♦ Jan 24 '14 at 19:32
    
@nux A bit late to the party, but from command line use adduser instead, useradd should be limited to scripts where the author really really knows what he is doing. – flindeberg Jul 24 '16 at 14:39

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.

community wiki

3  
It's useful to remember that getent doesn't just print the output of users in /etc/passwd but all users in all configured userdb backends on a given system, whether it's /etc/passwd or LDAP, etc. – Marcin Kaminski Sep 25 '14 at 16:34

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
community wiki

1  
Maybe you should explain the difference between adduser and useradd. An also add the sudo-prefix to the first command. The password shadow file can only be read as root. – the_Seppi Sep 25 '14 at 20:13

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.

community wiki

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.

answered Jan 24 '14 at 19:38

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.
4  
This only shows the content of /home. While Ubuntu puts user directories there by default, it's in no way mandatory. – David Foerster Dec 19 '14 at 0:57

protected by Radu Rădeanu Feb 22 '15 at 17:21

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