现象演示：

[www@localhost etc]$ useradd tester1
bash: /usr/sbin/useradd: Permission denied

解决方案：

1、在useradd命令前添加sudo命令。（若还是失败，情形如下图，则转向步骤2）

[www@localhost etc]$ sudo useradd tester1
[sudo] password for www:
www is not in the sudoers file.  This incident will be reported.

2、切换到root用户（su root）

①首先给sudoers文件添加write权限。(chmod u+w sudoers)

[root@localhost etc]# ls -l | grep sudoers
-r--r-----.  1 root root     4328 Oct 30  2018 sudoers
drwxr-x---.  2 root root        6 Oct 30  2018 sudoers.d
[root@localhost etc]# chmod u+w sudoers
[root@localhost etc]# ls -l | grep sudoers
-rw-r-----.  1 root root     4328 Oct 30  2018 sudoers
drwxr-x---.  2 root root        6 Oct 30  2018 sudoers.d

②再使用vi  /etc/sudoers 命令添加普通用户的操作权限。

## The COMMANDS section may have other options added to it.
##
## Allow root to run any commands anywhere
root    ALL=(ALL)       ALL
www     ALL=(ALL)       ALL   ## 添加此行

3、切换回普通用户

4、再使用命令 sudo useradd tester1即可运行成功，并在/etc/passwd中查看此用户。

[www@localhost etc]$ sudo useradd tester1
[sudo] password for www:
[www@localhost etc]$
[www@localhost etc]$ tail /etc/passwd
setroubleshoot:x:990:984::/var/lib/setroubleshoot:/sbin/nologin
saned:x:989:983:SANE scanner daemon user:/usr/share/sane:/sbin/nologin
gdm:x:42:42::/var/lib/gdm:/sbin/nologin
gnome-initial-setup:x:988:982::/run/gnome-initial-setup/:/sbin/nologin
sshd:x:74:74:Privilege-separated SSH:/var/empty/sshd:/sbin/nologin
avahi:x:70:70:Avahi mDNS/DNS-SD Stack:/var/run/avahi-daemon:/sbin/nologin
postfix:x:89:89::/var/spool/postfix:/sbin/nologin
tcpdump:x:72:72::/:/sbin/nologin
www:x:1000:1000:www:/home/www:/bin/bash
tester1:x:1001:1001::/home/tester1:/bin/bash