Linux-Basics-Complete-Course-With-Notes-Slides

LINUX ACCOUNTS

In this section we will take a look at basic access control in Linux.
We will also learn about about the file permissions. Lets Get Started!

#### User Accounts

User’s informations are stored under /etc/passwd file.
```
[~]$ cat /etc/passwd
```
Information about groups is stored into /etc/group file.
```
[~]$ cat /etc/group
```
Each user has a username and a unique ID assigned to them known as user ID or UID.
The user also has a GID, the group id they are part of, id command can be use to check these details. for eg:
```
[~]$ id michael
uid=1001(michael) gid=1001(michael)groups=1001(michael),1003(developers)
```
More details about the user account can be found eg. default shell, home directory using.
```
[~]$ grep -i michael /etc/passwd
michael:x:1001:1001::/home/michael:/bin/sh
```
To see the list of users currently logged use who command.
```
[~]$ who
bob pts/2 Apr 28 06:48 (172.16.238.187)
```

The last command displays the record of all logged-in users along with the date and time when the system was rebooted.

[~]$ last
michael :1 :1 Tue May 12 20:00 still logged in
sarah :1 :1 Tue May 12 12:00 still running
reboot system boot 5.3.0-758-gen Mon May 11 13:00 - 19:00 (06:00)

#### Switching users

To switch to any user use su command.
```
[~]$ su –
Password:

root ~#
```
To run a specific command you can use su -c "whoami" (This is not recommended way)
```
[michael@ubuntu-server ~]$ su -c "whoami"
Password:
root
```

To run a command as a root user sudo command is recommended.

[michael@ubuntu-server ~]$ sudo apt-get install nginx
[sudo] password for michael:

who

Users listed in /etc/sudoers file can make use of sudo command for privledge escalation.
```
[~]$ cat /etc/sudoers
```
To restrict anyone from directly login as root login, this can be done by setting nologin shell.
```
[~]$ grep -i ^root /etc/passwd
/root:x:0:0:root:/root:/usr/sbin/nologin
```