Linux study notes_2: user management + practical instructions

User Management

Linux system is a multi-user multi-tasking operating system, a user want to use any system resources, must first apply for a user account to the system administrator, and then enter the system as a user of this account; at least Linux users to belong A group.

• Add user

  • useradd [-d] bcxtm, Add the user account of bcxtm (default /home/bcxtm) ,, -dadd to the specified directory

    If the group to which the new user belongs is not specified, a group consistent with the user name will be created by default

• Assign/modify password

  • passwd bcxtm, Interactively set the password, only the root user has this authority

• delete users

  • userdel [-r] bcxtm, Delete the user account of bcxtm, keep the user directory,, -rcascade to delete the user directory

• Query user information

  • id bcxtmDisplayed uid, gid,所在组别名称

• Switch user

  • su - bcxtm, Used su -by non-root users , switch users as an administrator

    No password verification is required to switch from high authority to low authority, and vice versa; use exit to switch to the original user.

• User group (similar to the concept of role, common users belong to a group)

  • Add group:groupadd groupName
  • Delete group:groupdel groupName
  • Specify the group when creating a user:useradd -g groupName userName
  • Modify user group:usermod -g newGroupName userName
  • User and group relationship configuration storage
    • User profile:/etc/passwd
      • Username: Password: User Identification Number: Group Identification Number: Annotative Description: Home Directory: Login Shell
    • Group configuration file:/etc/group
      • Group name: Password: Group identification number: List of users in the group
    • Password (encrypted login and password information) configuration file:/etc/shadow
      • Username: encrypted password: last modification time: minimum time interval: maximum time interval: warning time: inactivity time: expiration time: sign

Practical instructions

• Run level concept (configuration file in /etc/inittab)

  • 0: Shut down
  • 1: Single user
  • 2: Multi-user no network service
  • 3：Multiple users have network services (commonly used)
  • 4: System reserved
  • 5: Graphical interface (commonly used)
  • 6: Restart

• Specify run level

  • init [0-6]

• How to retrieve root password?

  Enter single-user mode (login without a password), just change the root user password!

• Help instruction

  • man + 指令
  • help + 指令