linux普通用户添加root权限

　　新增一个普通用户并进入该用户：

[root@VM_0_7_centos ~]# groupadd mall
[root@VM_0_7_centos ~]# useradd mall -m -d /home/mall -g mall -s /bin/bash
[root@VM_0_7_centos ~]# passwd mall
Changing password for user mall.
New password:
BAD PASSWORD: The password is shorter than  characters
Retype new password:
passwd: all authentication tokens updated successfully.
[root@VM_0_7_centos ~]# su - mall

　　安装yum-utils失败了，提示需要root权限：

[mall@VM_0_7_centos ~]$ yum install -y yum-utils device-mapper-persistent-data lvm2
Loaded plugins: fastestmirror, langpacks
You need to be root to perform this command.

　　使用sudo获取root权限：

[mall@VM_0_7_centos ~]$ sudo yum install -y yum-utils device-mapper-persistent-data lvm2

We trust you have received the usual lecture from the local System
Administrator. It usually boils down to these three things:

    #) Respect the privacy of others.
    #) Think before you type.
    #) With great power comes great responsibility.

[sudo] password for mall:
mall is not in the sudoers file.  This incident will be reported.

　　它说该普通用户没有在sudoers文件里，切换回root：

[mall@VM_0_7_centos ~]$ su - root
Password:
Last login: Wed Oct  :: CST  from 202.101.145.54 on pts/
Last failed login: Wed Oct  :: CST  from 110.119.120.10 on ssh:notty
There were  failed login attempts since the last successful login.

　　修改sudoers文件，加入写权限：

[root@VM_0_7_centos ~]# chmod +w /etc/sudoers
[root@VM_0_7_centos ~]# vi /etc/sudoers

　　新增下面标红的那一行，把普通用户mall加进入：

　　敲:wq保存后，撤销sudoers文件写权限：

[root@VM_0_7_centos ~]# chmod -w /etc/sudoers

　　重新进入mall用户，下载yum-utils：

[root@VM_0_7_centos ~]# su - mall
Last login: Wed Oct  :: CST  on pts/
[mall@VM_0_7_centos ~]$ sudo yum -y install yum-utils device-mapper-persistent-data 1vm2
[sudo] password for mall:
Loaded plugins: fastestmirror, langpacks
Loading mirror speeds from cached hostfile
Package yum-utils-1.1.-.el7.noarch already installed and latest version
Package device-mapper-persistent-data-0.8.-.el7.x86_64 already installed and latest version
No package 1vm2 available.
Nothing to do

　　这回可以了，不过其实已经安装过了，白折腾了。