sudo配置临时取得root权限

sudo配置临时取得root权限
系统中的普通用户有时须要root权限执行某种操做，要是使用su - root的话必需要知道root的密码，这是不安全的，因此有了sudo，root能够对/etc/sudoers作必定的配置，让普通用户
在不切换到root的状况下，执行一些只有root才能执行的操做。这个文件只能root去修改，建议使用visudo这个命令修改，而不是直接vim /etc/sudoers。
缘由有二：
◦ 一是它可以防止两个用户同时修改它；
◦ 二是它也能进行有限的语法检查。
当编辑这个文件有错误时，使用visudo会给出错误提示，此时能够按e从新编辑，x不保存退出，Q保存退出，若是选择Q，sudo就不能正常工做了。

实验过程完成了给指定用户sudo权限和用别名指定一组用户的能够执行的sudo指令

过程以下：

 

[root@mail ~]# visudo

#chen为普通用户，ALL能够从任何的主机登录，(root)能够以root身份，后面是能够执行的命令，最好写全路径
     88 ## Allow root to run any commands anywhere
     89 root    ALL=(ALL)       ALL
     90 chen    ALL=(root)      /usr/sbin/useradd,/usr/bin/passwd
     91 ## Allows members of the 'sys' group to run networking, software,


[root@mail ~]# exit
logout
[chen@mail 桌面]$ sudo -l #查看本身能够执行的sudo命令
[sudo] password for chen:   #输入本身的密码
Matching Defaults entries for chen on this host:
    requiretty, always_set_home, env_reset, env_keep="COLORS DISPLAY HOSTNAME
    HISTSIZE INPUTRC KDEDIR LS_COLORS", env_keep+="MAIL PS1 PS2 QTDIR USERNAME
    LANG LC_ADDRESS LC_CTYPE", env_keep+="LC_COLLATE LC_IDENTIFICATION
    LC_MEASUREMENT LC_MESSAGES", env_keep+="LC_MONETARY LC_NAME LC_NUMERIC
    LC_PAPER LC_TELEPHONE", env_keep+="LC_TIME LC_ALL LANGUAGE LINGUAS
    _XKB_CHARSET XAUTHORITY", secure_path=/sbin\:/bin\:/usr/sbin\:/usr/bin

User chen may run the following commands on this host:
    (root) /usr/sbin/useradd, (root) /usr/bin/passwd    #这里看到能够执行的sudo命令
[chen@mail 桌面]$ sudo useradd user3  #测试
[chen@mail 桌面]$ sudo passwd user3
更改用户 user3 的密码 。
新的 密码：
无效的密码： 太短
无效的密码： 过于简单
从新输入新的 密码：
passwd： 全部的身份验证令牌已经成功更新。
[chen@mail 桌面]$ id user3    #添加user3成功
uid=503(user3) gid=503(user3) 组=503(user3)
[chen@mail 桌面]$ visudo  #普通用户不容许编辑
visudo: /etc/sudoers: Permission denied
visudo: /etc/sudoers: Permission denied
[chen@mail 桌面]$ su - root
密码：
[root@mail ~]# visudo
[root@mail ~]# cat /etc/sudoers |grep user1 #编辑增长了下面一行
user1   ALL=(user2) /bin/ls
[root@mail ~]# su - user1
[user1@mail ~]$ sudo -l

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

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

[sudo] password for user1:
Matching Defaults entries for user1 on this host:
    requiretty, always_set_home, env_reset, env_keep="COLORS DISPLAY HOSTNAME
    HISTSIZE INPUTRC KDEDIR LS_COLORS", env_keep+="MAIL PS1 PS2 QTDIR USERNAME
    LANG LC_ADDRESS LC_CTYPE", env_keep+="LC_COLLATE LC_IDENTIFICATION
    LC_MEASUREMENT LC_MESSAGES", env_keep+="LC_MONETARY LC_NAME LC_NUMERIC
    LC_PAPER LC_TELEPHONE", env_keep+="LC_TIME LC_ALL LANGUAGE LINGUAS
    _XKB_CHARSET XAUTHORITY", secure_path=/sbin\:/bin\:/usr/sbin\:/usr/bin

User user1 may run the following commands on this host:
    (user2) /bin/ls
[user1@mail ~]$ ls /home/user2  #user1直接查看user2的家目录确定是不容许的
ls: 没法打开目录/home/user2: 权限不够
[user1@mail ~]$ sudo -u user2 ls /home/user2    #可是sudo以user2的身份查看就能够
a

#这里不能以user2的身份添加用户，由于user2自己尚未useradd的权限
#事实上，即便给user2 sudo的添加用户权限这样也是不行的，由于user2添加的时候也要sudo的啊
#直接以user2确定不行，看演示。
[user1@mail ~]$ sudo -u user2 useradd user4 #这时候不能添加
Sorry, user user1 is not allowed to execute '/usr/sbin/useradd user4' as user2 on mail.example.com.
[user1@mail ~]$ exit
logout
[root@mail ~]# visudo
#添加了这行，给user2 sudo添加用户的权限，这时候sudo -u user2 useradd user4是否能够呢？不行的！
 user2   ALL=(root)      /usr/sbin/useradd,/usr/bin/passwd
[root@mail ~]# su - user2
[user2@mail ~]$ sudo -l

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

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

[sudo] password for user2:
Matching Defaults entries for user2 on this host:
    requiretty, always_set_home, env_reset, env_keep="COLORS DISPLAY HOSTNAME
    HISTSIZE INPUTRC KDEDIR LS_COLORS", env_keep+="MAIL PS1 PS2 QTDIR USERNAME
    LANG LC_ADDRESS LC_CTYPE", env_keep+="LC_COLLATE LC_IDENTIFICATION
    LC_MEASUREMENT LC_MESSAGES", env_keep+="LC_MONETARY LC_NAME LC_NUMERIC
    LC_PAPER LC_TELEPHONE", env_keep+="LC_TIME LC_ALL LANGUAGE LINGUAS
    _XKB_CHARSET XAUTHORITY", secure_path=/sbin\:/bin\:/usr/sbin\:/usr/bin

User user2 may run the following commands on this host:
    (root) /usr/sbin/useradd, (root) /usr/bin/passwd
[user2@mail ~]$ su - user1
密码：
[user1@mail ~]$ sudo -u user2 useradd user4 #答案在此，不行的！
Sorry, user user1 is not allowed to execute '/usr/sbin/useradd user4' as user2 on mail.example.com.
[user1@mail ~]$
#总结下，sudo -u 用户名 命令 ，当前用户以某个用户的身份执行某个命令的时候，必须这个用户自己不加sudo的状况
#直接能执行的命令，才能够这种方式执行。另外，sudo不加-u，默认以root身份执行

[user1@mail ~]$ exit
logout
[user2@mail ~]$ exit
logout
[root@mail ~]# visudo
#改动以下：删除了91，92行，
     88 ## Allow root to run any commands anywhere
     89 root    ALL=(ALL)       ALL
     90 chen    ALL=(root)      /usr/sbin/useradd,/usr/bin/passwd
     91 user1   ALL=(user2)     /bin/ls     #删除
     92 user2   ALL=(root)      /usr/sbin/useradd,/usr/bin/passwd   #删除

     88 ## Allow root to run any commands anywhere
     89 root    ALL=(ALL)       ALL
     90 chen    ALL=(root)      /usr/sbin/useradd,/usr/bin/passwd
     91 ADMIN   ALL=(root)      /usr/sbin/useradd,/usr/bin/passwd   #新添加

     20 # User_Alias ADMINS = jsmith, mikem
     21  User_Alias ADMIN = user1, user2        #新添加
     22
#这里至关于ADMIN为user1，user2的别名，这个别名具备添加用户的权限，user1和user2也具备这个权限
[root@mail ~]# su - user1
[user1@mail ~]$ sudo -l
[sudo] password for user1:
Matching Defaults entries for user1 on this host:
    requiretty, always_set_home, env_reset, env_keep="COLORS DISPLAY HOSTNAME
    HISTSIZE INPUTRC KDEDIR LS_COLORS", env_keep+="MAIL PS1 PS2 QTDIR USERNAME
    LANG LC_ADDRESS LC_CTYPE", env_keep+="LC_COLLATE LC_IDENTIFICATION
    LC_MEASUREMENT LC_MESSAGES", env_keep+="LC_MONETARY LC_NAME LC_NUMERIC
    LC_PAPER LC_TELEPHONE", env_keep+="LC_TIME LC_ALL LANGUAGE LINGUAS
    _XKB_CHARSET XAUTHORITY", secure_path=/sbin\:/bin\:/usr/sbin\:/usr/bin

User user1 may run the following commands on this host:
    (root) /usr/sbin/useradd, (root) /usr/bin/passwd    #能够看到user1有useradd权限
[user1@mail ~]$ su - user2
密码：
[user2@mail ~]$ sudo -l
[sudo] password for user2:
Matching Defaults entries for user2 on this host:
    requiretty, always_set_home, env_reset, env_keep="COLORS DISPLAY HOSTNAME
    HISTSIZE INPUTRC KDEDIR LS_COLORS", env_keep+="MAIL PS1 PS2 QTDIR USERNAME
    LANG LC_ADDRESS LC_CTYPE", env_keep+="LC_COLLATE LC_IDENTIFICATION
    LC_MEASUREMENT LC_MESSAGES", env_keep+="LC_MONETARY LC_NAME LC_NUMERIC
    LC_PAPER LC_TELEPHONE", env_keep+="LC_TIME LC_ALL LANGUAGE LINGUAS
    _XKB_CHARSET XAUTHORITY", secure_path=/sbin\:/bin\:/usr/sbin\:/usr/bin

User user2 may run the following commands on this host:
    (root) /usr/sbin/useradd, (root) /usr/bin/passwd    #user2也有
[user2@mail ~]$