系统运维-23-3-Sudo基础知识

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本文介绍了Sudo的基础知识，包括其用于允许用户以其他用户身份运行命令的功能，重点讨论了`sudoers`配置文件的结构和权限设置。内容涵盖用户、主机、命令和别名配置项，以及如何编辑配置文件以授权特定用户执行特定命令。示例中展示了如何为用户分配权限，以及如何使用NOPASSWD选项进行无密码执行。

SUDO的基础知识

su： Switch User

sudo
可以让某个用户不用拥有另外一个账户的账号和密码，就可以执行操作
授权之后，能够让某用户以另外一个用户的身份运行命令

注意：ubuntu等有时会限制 su - 为管理员，但 sudo su - 依然可以切换

配置文件：sudoers
root ALL=(ALL) ALL
%wheel ALL=(ALL) ALL

   who 运行命令者的身份 user
   where 通过哪些主机 host
   (whom) 以哪个用户的身份 runas
   which 运行哪些命令 command

配置项
user hosts=(runas) commands

       users:
           username
           #uid
           user_alias
           %group_name
           %#gid

       hosts：
           ip
           hostname
           netaddr

       command：
           command name
           directory
           sudoedit

           Alias_Type NAME = item1, item2, ...
               NAME必须使用全大写字母
           Alias_Type
               User_Alias
               Runas_Alias
               Host_Alias
               Cmnd_Alias

       sudo COMMAND
           -u user 默认为root
           -k 清除此前记录的登录密码

查看默认的配置文件

   [root@lab1 ~]# ll /etc | grep sudoers
   -r--r-----. 1 root root 3938 Jun 7 2017 sudoers
   drwxr-x---. 2 root root 6 Aug 4 2017 sudoers.d
   [root@lab1 ~]# grep -v ^# /etc/sudoers | grep -v ^$
   Defaults !visiblepw
   Defaults always_set_home
   Defaults match_group_by_gid
   Defaults env_reset
   Defaults env_keep = "COLORS DISPLAY HOSTNAME HISTSIZE KDEDIR LS_COLORS"
   Defaults env_keep += "MAIL PS1 PS2 QTDIR USERNAME LANG LC_ADDRESS LC_CTYPE"
   Defaults env_keep += "LC_COLLATE LC_IDENTIFICATION LC_MEASUREMENT LC_MESSAGES"
   Defaults env_keep += "LC_MONETARY LC_NAME LC_NUMERIC LC_PAPER LC_TELEPHONE"
   Defaults env_keep += "LC_TIME LC_ALL LANGUAGE LINGUAS _XKB_CHARSET XAUTHORITY"
   Defaults secure_path = /sbin:/bin:/usr/sb[root@lab1 ~]# sudo -u user001 whoami
   user001
   in:/usr/bin
   root   ALL=(ALL)    ALL
   %wheel   ALL=(ALL)   ALL
   [root@lab1 ~]# sudo -u user001 whoami
   user001
   [root@lab1 ~]# whoami
   root

测试默认权限

   [user001@lab1 ~]$ fdisk -l
   fdisk: cannot open /dev/sda: Permission denied
   fdisk: cannot open /dev/sr0: Permission denied
   fdisk: cannot open /dev/mapper/centos-root: Permission denied
   fdisk: cannot open /dev/mapper/centos-swap: Permission denied
   [user001@lab1 ~]$ sudo fdisk -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 user001:
   user001 is not in the sudoers file. This incident will be reported.

   [root@lab1 ~]# usermod -a -G wheel user001
   You have new mail in /var/spool/mail/root
   [root@lab1 ~]# id user001
   uid=1025(user001) gid=1025(user001) groups=1025(user001),10(wheel)

   Disk /dev/sda: 21.5 GB, 21474836480 bytes, 41943040 sectors
   Units = sectors of 1 * 512 = 512 bytes
   Sector size (logical/physical): 512 bytes / 512 bytes
   I/O size (minimum/optimal): 512 bytes / 512 bytes
   Disk label type: dos
   Disk identifier: 0x000a2c70

   Device Boot Start End Blocks Id System
   /dev/sda1 * 2048 2099199 1048576 83 Linux
   /dev/sda2 2099200 41943039 19921920 8e Linux LVM

   Disk /dev/mapper/centos-root: 18.2 GB, 18249416704 bytes, 35643392 sectors
   Units = sectors of 1 * 512 = 512 bytes
   Sector size (logical/physical): 512 bytes / 512 bytes
   I/O size (minimum/optimal): 512 bytes / 512 bytes

   Disk /dev/mapper/centos-swap: 2147 MB, 2147483648 bytes, 4194304 sectors
   Units = sectors of 1 * 512 = 512 bytes
   Sector size (logical/physical): 512 bytes / 512 bytes
   I/O size (minimum/optimal): 512 bytes / 512 bytes

编辑配置文件

   [root@lab1 ~]# tail -4 /etc/sudoers
   User_Alias NETADMIN = netuser1,netuser2
   Cmnd_Alias NETADMINCMND = /usr/sbin/ip

NETADMIN ALL=(root) NETADMINCMND

创建用户账号

   [root@lab1 ~]# useradd netuser1
   [root@lab1 ~]# useradd netuser2
   [root@lab1 ~]# echo "redhat" | passwd --stdin netuser1
   Changing password for user netuser1.
   passwd: all authentication tokens updated successfully.
   [root@lab1 ~]# echo "redhat" | passwd --stdin netuser2
   Changing password for user netuser2.
   passwd: all authentication tokens updated successfully.

切换用户查看授权

[root@lab1 ~]# su - netuser1
[netuser1@lab1 ~]$ 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 netuser1:
   Matching Defaults entries for netuser1 on lab1:
   !visiblepw, always_set_home, match_group_by_gid, env_reset, env_keep="COLORS
   DISPLAY HOSTNAME HISTSIZE 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 netuser1 may run the following commands on lab1:
(root) /usr/sbin/ip

指定用户的权限测试

   [netuser1@lab1 ~]$ sudo ip addr
   1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN qlen 1
   link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
   inet 127.0.0.1/8 scope host lo
   valid_lft forever preferred_lft forever
   inet6 ::1/128 scope host
   valid_lft forever preferred_lft forever
   2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
   link/ether 00:0c:29:b0:6e:59 brd ff:ff:ff:ff:ff:ff
   inet 172.20.0.131/24 brd 172.20.0.255 scope global dynamic ens33
   valid_lft 1264sec preferred_lft 1264sec
   inet6 fe80::3e66:b2a:5133:93d1/64 scope link
   valid_lft forever preferred_lft forever
   [netuser1@lab1 ~]$ sudo route -n
   Sorry, user netuser1 is not allowed to execute '/sbin/route -n' as root on lab1.example.com.

清除检票

[netuser1@lab1 ~]$ sudo -k

特殊权限（限制改管理员密码）

   [root@lab1 ~]# tail -5 /etc/sudoers
   User_Alias USERADMIN = poweruser1,poweruser2
   Cmnd_Alias USERADMINCMND = /usr/sbin/useradd, /usr/sbin/usermod, /usr/bin/passwd

USERADMIN ALL=(root) NOPASSWD:USERADMINCMND

   [root@lab1 ~]# useradd poweruser1
   [root@lab1 ~]# su - poweruser1
   [poweruser1@lab1 ~]$ sudo -l
   Matching Defaults entries for poweruser1 on lab1:
   !visiblepw, always_set_home, match_group_by_gid, env_reset, env_keep="COLORS
   DISPLAY HOSTNAME HISTSIZE 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 poweruser1 may run the following commands on lab1:
   (root) NOPASSWD: /usr/sbin/useradd, /usr/sbin/usermod, /usr/bin/passwd
   [poweruser1@lab1 ~]$ useradd testuser
   -bash: /usr/sbin/useradd: Permission denied
   [poweruser1@lab1 ~]$ sudo useradd testuser
   oot@lab1 ~]# tail -4 /etc/sudoers
   Cmnd_Alias USERADMINCMND = /usr/sbin/useradd, /usr/sbin/usermod, /usr/bin/passwd [a-z]*, !/usr/bin/passwd root

USERADMIN ALL=(root) NOPASSWD:USERADMINCMND

   [root@lab1 ~]# su - poweruser1
   Last login: Wed May 8 07:25:35 EDT 2019 on pts/0
   [poweruser1@lab1 ~]$ sudo passwd root
   Sorry, user poweruser1 is not allowed to execute '/bin/passwd root' as root on lab1.example.com.
   [poweruser1@lab1 ~]$ sudo passwd netuser1
   Changing password for user netuser1.
   New password:
   BAD PASSWORD: The password is shorter than 8 characters
   Retype new password:
   passwd: all authentication tokens updated successfully.