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需要root权限执行某种操作，要是使用su - root的话必须要知道root的密码，这是不安全的，所以有了sudo，root可以对/etc/sudoers做一定的配置，让普通用户
在不切换到root的情况下，执行一些只有root才能执行的操作。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。
原因有二：
◦ 一是它能够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，此时可以按e重新编辑，x不保存退出，Q保存退出，如果选择Q，sudo就不能正常工作了。

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可以执行的sudo指令

过程如下：

[root@mail ~]# visudo #chen为普通用户，ALL可以从任何的主机登陆，(root)可以以root身份，后面是可以执行的命令，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 ~]# exitlogout[chen@mail 桌面]$ sudo -l#查看自己可以执行的sudo命令[sudo] password for chen:#输入自己的密码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/binUser chen may run the following commands on this host:    (root) /usr/sbin/useradd, (root) /usr/bin/passwd#这里看到可以执行的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： 过短无效的密码： 过于简单重新输入新的 密码：passwd： 所有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#普通用户不允许编辑visudo: /etc/sudoers: Permission deniedvisudo: /etc/sudoers: Permission denied[chen@mail 桌面]$ su - root密码：[root@mail ~]# visudo [root@mail ~]# cat /etc/sudoers |grep user1#编辑增加了下面一行user1 ALL=(user2)/bin/ls[root@mail ~]# su - user1[user1@mail ~]$ sudo -lWe trust you have received the usual lecture from the local SystemAdministrator. 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/binUser user1 may run the following commands on this host:    (user2) /bin/ls[user1@mail ~]$ ls /home/user2#user1直接查看user2的家目录肯定是不允许的ls: 无法打开目录/home/user2: 权限不够[user1@mail ~]$ sudo -u user2 ls /home/user2#但是sudo以user2的身份查看就可以a#这里不能以user2的身份添加用户，因为user2本身还没有useradd的权限#事实上，即使给user2 sudo的添加用户权限这样也是不行的，因为user2添加的时候也要sudo的啊#直接以user2肯定不行，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 ~]$ exitlogout[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是否可以呢？不行的！ user2   ALL=(root)      /usr/sbin/useradd,/usr/bin/passwd[root@mail ~]# su - user2[user2@mail ~]$ sudo -lWe trust you have received the usual lecture from the local SystemAdministrator. 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/binUser 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，必须这个用户本身不加sudo的情况#直接能执行的命令，才可以这种方式执行。另外，sudo不加-u，默认以root身份执行[user1@mail ~]$ exitlogout[user2@mail ~]$ exitlogout[root@mail ~]# visudo #改动如下：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 #这里相当于ADMIN为user1，user2的别名，这个别名具有添加用户的权限，user1和user2也具有这个权限[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/binUser user1 may run the following commands on this host:    (root) /usr/sbin/useradd, (root) /usr/bin/passwd#可以看到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/binUser user2 may run the following commands on this host:    (root) /usr/sbin/useradd, (root) /usr/bin/passwd#user2也有[user2@mail ~]$