Linux_011：如何让普通用户有sudo的权限？

安装软件时有时需要root权限，把root密码告诉别人有很多隐患：
（1）不安全
（2）无法区分哪些操作是谁做的。
（3）密码分发问题。
总之，超级用户root密码应该只掌握在少数人手中。

这时，我们可以使用 sudo，把某些超级权限有针对性的下放，并且不需要普通用户知道root密码。
相对于权限无限制性的 su 来说，sudo 还是比较安全的，所以 sudo 也能被称为受限制的su。
另外 sudo 是需要授权许可的，所以也被称为授权许可的 su；
sudo执行命令的流程是当前用户切换到root（或其它指定切换到的用户），然后以 root（或其它指定的切换到的用户）身份执行命令，执行完成后，直接退回到当前用户；而这些的前提是要通过 sudo 的配置文件 /etc/sudoers 来进行授权。

查看/etc/sudoers

## Sudoers allows particular users to run various commands as
## the root user, without needing the root password.
##
## Examples are provided at the bottom of the file for collections
## of related commands, which can then be delegated out to particular
## users or groups.
##
## This file must be edited with the 'visudo' command.

## Host Aliases
## Groups of machines. You may prefer to use hostnames (perhaps using
## wildcards for entire domains) or IP addresses instead.
# Host_Alias     FILESERVERS = fs1, fs2
# Host_Alias     MAILSERVERS = smtp, smtp2

## User Aliases
## These aren't often necessary, as you can use regular groups
## (ie, from files, LDAP, NIS, etc) in this file - just use %groupname
## rather than USERALIAS
# User_Alias ADMINS = jsmith, mikem


## Command Aliases
## These are groups of related commands...

## Networking
# Cmnd_Alias NETWORKING = /sbin/route, /sbin/ifconfig, /bin/ping, /sbin/dhclient, /usr/bin/net, /sbin/iptables, /usr/bin/rfcomm, /usr/bin/wvdial, /sbin/iwconfig, /sbin/mii-tool

## Installation and management of software
# Cmnd_Alias SOFTWARE = /bin/rpm, /usr/bin/up2date, /usr/bin/yum

## Services
# Cmnd_Alias SERVICES = /sbin/service, /sbin/chkconfig

## Updating the locate database
# Cmnd_Alias LOCATE = /usr/bin/updatedb

## Storage
# Cmnd_Alias STORAGE = /sbin/fdisk, /sbin/sfdisk, /sbin/parted, /sbin/partprobe, /bin/mount, /bin/umount

## Delegating permissions
# Cmnd_Alias DELEGATING = /usr/sbin/visudo, /bin/chown, /bin/chmod, /bin/chgrp

## Processes
# Cmnd_Alias PROCESSES = /bin/nice, /bin/kill, /usr/bin/kill, /usr/bin/killall

## Drivers
# Cmnd_Alias DRIVERS = /sbin/modprobe

# Defaults specification

#
# Disable "ssh hostname sudo ", because it will show the password in clear. 
#         You have to run "ssh -t hostname sudo ".
#
Defaults    requiretty

#
# Refuse to run if unable to disable echo on the tty. This setting should also be
# changed in order to be able to use sudo without a tty. See requiretty above.
#
Defaults   !visiblepw

#
# Preserving HOME has security implications since many programs
# use it when searching for configuration files. Note that HOME
# is already set when the the env_reset option is enabled, so
# this option is only effective for configurations where either
# env_reset is disabled or HOME is present in the env_keep list.
#
Defaults    always_set_home

Defaults    env_reset
Defaults    env_keep =  "COLORS DISPLAY HOSTNAME HISTSIZE INPUTRC 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"

#
# Adding HOME to env_keep may enable a user to run unrestricted
# commands via sudo.
#
# Defaults   env_keep += "HOME"

Defaults    secure_path = /sbin:/bin:/usr/sbin:/usr/bin

## Next comes the main part: which users can run what software on
## which machines (the sudoers file can be shared between multiple
## systems).
## Syntax:
##
## user MACHINE=COMMANDS
##
## The COMMANDS section may have other options added to it.
##
## Allow root to run any commands anywhere
root ALL=(ALL) ALL

## Allows members of the 'sys' group to run networking, software,
## service management apps and more.
# %sys ALL = NETWORKING, SOFTWARE, SERVICES, STORAGE, DELEGATING, PROCESSES, LOCATE, DRIVERS

## Allows people in group wheel to run all commands
# %wheel ALL=(ALL) ALL

## Same thing without a password
# %wheel ALL=(ALL) NOPASSWD: ALL

## Allows members of the users group to mount and unmount the
## cdrom as root
# %users  ALL=/sbin/mount /mnt/cdrom, /sbin/umount /mnt/cdrom

## Allows members of the users group to shutdown this system
# %users  localhost=/sbin/shutdown -h now

## Read drop-in files from /etc/sudoers.d (the # here does not mean a comment)
#includedir /etc/sudoers.d
maping ALL=(root) NOPASSWD: ALL

在文件内容的最后一行，我给用户maping授予了sudo root用户的权限，密码永不过期。
你也可以给一个组授予sudo的权限，在组名前加“%”即可，比如：%wheel ALL=(ALL) NOPASSWD: ALL。

这样设置好了以后，以用户maping登录，就可以随时使用sudo命令执行root用户才能执行的命令。
比如：sudo vi /etc/profile，这时会提示输入口令（我这里设置成NOPASSWD，所以不需要输入），你只需要输入用户maping的口令就可以了，不需要输入root口令。
也就是说，你无须知道root口令就可以执行root用户才能执行的命令。
这就是使用sudo的好处。

另外，如果为了频繁的执行某些只有超级用户才能执行的权限，而不用每次输入密码，可以使用命令：sudo -i。提示输入密码时该密码为当前账户的密码。没有时间限制。
sudo -i 与 sudo 的区别是：sudo 是暂时切换到超级用户模式以执行超级用户权限，提示输入密码时该密码为当前用户的密码，而不是超级账户的密码。不过有时间限制，默认为一次时长 15 分钟。而 sudo -i 没有时间限制。

参考文献：

1. http://blog.csdn.net/trochiluses/article/details/8810010