Managing User Account

We have three primary files in /etc/ directory that are related to user account.

/etc/passwd file stores essential information, which is required during login i.e. user account information, a list of the system's accounts, giving for each account some useful information like user ID, group ID, home directory, shell, etc. The /etc/passwd contains one entry per line for each user (or user account) of the system. All fields are separated by a colon (:) symbol. Total seven fields:

root:x:0:0:root:/root:/bin/bash
jenkins:x:120:128:Jenkins,,,:/var/lib/jenkins:/bin/bash
tomcat7:x:121:129::/usr/share/tomcat7:/bin/false
k:x:1000:1000:k,,,:/home/k:/bin/bash

1. Username
2. Password
3. User ID (UID): Each user must be assigned a user ID (UID). UID 0 (zero) is reserved for root and UIDs 1-99 are reserved for other predefined accounts. Further UID 100-999 are reserved by system for administrative and system accounts/groups.
4. Group ID (GID): The primary group ID (stored in /etc/group file)
5. User ID Info: The comment field. It allow usu to add extra information about the users such as user's full name, phone number etc. This field use by finger command.
6. Home directory: The absolute path to the directory the user will be in when they log in. If this directory does not exists then users directory becomes /
7. Command/shell: The absolute path of a command or shell (/bin/bash).

k@laptop:~$ tail /etc/shadow
tail: cannot open '/etc/shadow' for reading: Permission denied

k@laptop:~$ su -i
root@laptop:/home/bogo# tail /etc/shadow
root:!:16203:0:99999:7:::
k:$6$d9C.Shbj$M2ptKv3YiS5efYO7yY0YKYu2DWbR4N.8auDIWFRyPFaqgPdfJiID/nPVk1cscVhDSA.parzgg79CwXzJOCL431:16203:0:99999:7:::
postgres:*:16223:0:99999:7:::
mongodb:*:16263:0:99999:7:::

/etc/group defines the groups to which users belong. Multiple users can be categorized into groups. The file system permissions are organized into three classes, user, group, and others. The use of groups allows additional abilities to be delegated in an organized fashion, such as access to disks, printers, and others.

root:x:0:
daemon:x:1:
bin:x:2:
sys:x:3:
adm:x:4:syslog,k
tty:x:5:
disk:x:6:
lp:x:7:
mail:x:8:
news:x:9:
uucp:x:10:

It has 4 fields:

1. group_name
2. Password
3. Group ID (GID): Each user must be assigned a group ID. We can see this number in our /etc/passwd file.
4. Group List: It is a list of user names of users who are members of the group.

Now we want to create a user.

root@laptop:/home/bogo# useradd -m -d /home/bogo -s /bin/bash bogo

where

1. -m : Create the user's home directory if it does not exist.
2. -d HOME_DIR : The new user will be created using HOME_DIR as the value for the user's login directory.
3. -s SHELL The name of the user's login shell

We can see the changes in the files we discussed in the previous sections.

root@laptop:/home/bogo# tail /etc/passwd
...
bogo:x:1005:1007::/home/bogo:/bin/bash

root@laptop:/home/bogo# tail /etc/shadow
...
bogo:!:16413:0:99999:7:::

root@laptop:/home/bogo# cd /home/bogo
root@laptop:/home/bogo# ls
examples.desktop

The 'examples.desktop' has been automatically created. It is actually from /etc/skel:

root@laptop:/home/bogo# ls /etc/skel
examples.desktop

Let's look into the /home/ directory:

root@laptop:/home/bogo# ls -l /home
total 20
drwxr-xr-x   2 bogo    bogo     4096 Dec  8 20:53 bogo
drwxr-xr-x 106 k       k        4096 Dec  8 18:02 k
drwxr-xr-x   3 ubuntu  ubuntu   4096 Dec  5 21:05 ubuntu

To check the group 'bogo' belongs:

root@laptop:/home/bogo# grep bogo /etc/group
bogo:x:1007:

To set the password for 'bogo':

root@laptop:/home/bogo# passwd bogo
Enter new UNIX password: 
Retype new UNIX password: 
passwd: password updated successfully

root@laptop:/home/bogo# tail /etc/shadow
...
bogo:$6$WIsKtb8H$zrRWIZ4w/tYN5QMlMlKpwxpqCtYiDk9rqLGsu.wBK6LWLivx.IbXXyurkay3fZ5CW7IKSG.7IMvSF/z.IrfMv/:16413:0:99999:7:::
root@laptop:/home/bogo# 

Now, we see the account for 'bogo' is no longer locked.

But if we want to lock it:

root@laptop:/home/bogo# usermod -L bogo
root@laptop:/home/bogo# tail /etc/shadow
...
bogo:!$6$WIsKtb8H$zrRWIZ4w/tYN5QMlMlKpwxpqCtYiDk9rqLGsu.wBK6LWLivx.IbXXyurkay3fZ5CW7IKSG.7IMvSF/z.IrfMv/:16413:0:99999:7:::
root@laptop:/home/bogo# 

We can see the ! in the password field. To unlock we use -U switch:

root@laptop:/home/bogo# usermod -U bogo
root@laptop:/home/bogo# tail /etc/shadow
...
bogo:$6$WIsKtb8H$zrRWIZ4w/tYN5QMlMlKpwxpqCtYiDk9rqLGsu.wBK6LWLivx.IbXXyurkay3fZ5CW7IKSG.7IMvSF/z.IrfMv/:16413:0:99999:7:::
root@laptop:/home/bogo# 

The ! is gone again. Unlocked.

root@laptop:/home/bogo# usermod -U bogo
root@laptop:/home/bogo# tail /etc/shadow
...
bogo:$6$WIsKtb8H$zrRWIZ4w/tYN5QMlMlKpwxpqCtYiDk9rqLGsu.wBK6LWLivx.IbXXyurkay3fZ5CW7IKSG.7IMvSF/z.IrfMv/:16413:0:99999:7:::
root@laptop:/home/bogo# 

Now we want to delete the 'bogo' user we created.

root@laptop:/home/bogo# userdel bogo

After this command, there is no 'bogo' in both /etc/passwd and /etc/shadow files. However, it's still in /home directory:

root@laptop:/home/bogo# ls /home
bogo  k  ubuntu

root@laptop:/home/bogo# ls -l /home
drwxr-xr-x   2    1005     1007 4096 Dec  8 20:53 bogo
drwxr-xr-x 106 k       k        4096 Dec  8 18:02 k
drwxr-xr-x   3 ubuntu  ubuntu   4096 Dec  5 21:05 ubuntu

So, we need to clean that up:

root@laptop:/home/bogo# rm -rf /home/bogo