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LINUX ACCOUNTS

  • Take me to the Tutorial

  • 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!

    linux

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
    

    user

  • 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
    

    group

  • 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
    

    sudo

  • 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