sudo的作用，它允许经过同意的使用者以超级管理员的身份执行指定指令。sudo 的主要配置文件是/etc/sudoers,编辑文件时最好使用visudo,它会对语法进行简单的校验，并且防止多个程序同时编辑该文件
sudo 有4个字段
例如：
第一字段 第二字段 第三字段 第四字段
root ALL (ALL) ALL
第一个字段指明哪个用户可使用sudo，这里是root
第二个字段指明主机(可以是主机名或主机的IP地址)，这里ALL表示所有机器
第三个字段指明以哪个用户（可以使用用户别名），(ALL)指所有用户
第四个字段指明执行的命令（也可使用Cmd alias），ALL指任何指令
执行sudo指令后，在5分钟内若再次使用sudo不用输入当前用户的密码，为了安全可取消这个功能，使用参数“-k”
#sudo -k cmd
使用方法：
使用方式：
sudo -V 显示版本号
sudo -h 显示版本号及指令使用方式说明
sudo -l 显示出自己的权限
sudo -v 因为sudo在第一次执行时或是在N分钟内没有执行（N预设为5）会问密码，这个参数是重新做一
次确认，如果超过N分钟，也会问密码
sudo -k 将会强迫使用者在下一次执行sudo时问密码（不论有没有超过 N 分钟）
sudo -b 将要执行的指令放在后台执行
sudo -s 执行环境变数中的 SHELL 所指定的 shell ，或是 /etc/passwd 里所指定的 shell
sudo -H 将环境变数中的 HOME（家目录）指定为要变更身份的使用者家目录（如不加-u参数就是系统管
理者root）
实例介绍：
原文：
# Sample /etc/sudoers file.
#
# This file MUST be edited with the 'visudo' command as root.
#
# See the sudoers man page for the details on how to write a sudoers file.
#
##
# User alias specification
##
User_Alias FULLTIMERS = millert, mikef, dowdy
User_Alias PARTTIMERS = bostley, jwfox, crawl
User_Alias WEBMASTERS = will, wendy, wim
##
# Runas alias specification
##
Runas_Alias OP = root, operator
Runas_Alias DB = oracle, sybase
##
# Host alias specification
##
Host_Alias SPARC = bigtime, eclipse, moet, anchor:\
SGI = grolsch, dandelion, black:\
ALPHA = widget, thalamus, foobar:\
HPPA = boa, nag, python
Host_Alias CUNETS = 128.138.0.0/255.255.0.0
Host_Alias CSNETS = 128.138.243.0, 128.138.204.0/24, 128.138.242.0
Host_Alias SERVERS = master, mail, www, ns
Host_Alias CDROM = orion, perseus, hercules
##
# Cmnd alias specification
##
Cmnd_Alias DUMPS = /usr/sbin/dump, /usr/sbin/rdump, /usr/sbin/restore, \
/usr/sbin/rrestore, /usr/bin/mt
Cmnd_Alias KILL = /usr/bin/kill
Cmnd_Alias PRINTING = /usr/sbin/lpc, /usr/bin/lprm
Cmnd_Alias SHUTDOWN = /usr/sbin/shutdown
Cmnd_Alias HALT = /usr/sbin/halt, /usr/sbin/fasthalt
Cmnd_Alias REBOOT = /usr/sbin/reboot, /usr/sbin/fastboot
Cmnd_Alias SHELLS = /usr/bin/sh, /usr/bin/csh, /usr/bin/ksh, \
/usr/local/bin/tcsh, /usr/bin/rsh, \
/usr/local/bin/zsh
Cmnd_Alias SU = /usr/bin/su
Cmnd_Alias VIPW = /usr/sbin/vipw, /usr/bin/passwd, /usr/bin/chsh, \
/usr/bin/chfn
##
# Override built-in defaults
##
Defaults syslog=auth
Defaults:FULLTIMERS !lecture
Defaults:millert !authenticate
Defaults@SERVERS log_year, logfile=/var/log/sudo.log
##
# User specification
##
# root and users in group wheel can run anything on any machine as any user
root ALL = (ALL) ALL
%wheel ALL = (ALL) ALL
# full time sysadmins can run anything on any machine without a password
FULLTIMERS ALL = NOPASSWD: ALL
# part time sysadmins may run anything but need a password
PARTTIMERS ALL = ALL
# jack may run anything on machines in CSNETS
jack CSNETS = ALL
# lisa may run any command on any host in CUNETS (a class B network)
lisa CUNETS = ALL
# operator may run maintenance commands and anything in /usr/oper/bin/
operator ALL = DUMPS, KILL, PRINTING, SHUTDOWN, HALT, REBOOT,\
/usr/oper/bin/
# joe may su only to operator
joe ALL = /usr/bin/su operator
# pete may change passwords for anyone but root on the hp snakes
pete HPPA = /usr/bin/passwd [A-z]*, !/usr/bin/passwd root
# bob may run anything on the sparc and sgi machines as any user
# listed in the Runas_Alias "OP" (ie: root and operator)
bob SPARC = (OP) ALL : SGI = (OP) ALL
# jim may run anything on machines in the biglab netgroup
jim +biglab = ALL
# users in the secretaries netgroup need to help manage the printers
# as well as add and remove users
+secretaries ALL = PRINTING, /usr/bin/adduser, /usr/bin/rmuser
# fred can run commands as oracle or sybase without a password
fred ALL = (DB) NOPASSWD: ALL
# on the alphas, john may su to anyone but root and flags are not allowed
john ALPHA = /usr/bin/su [!-]*, !/usr/bin/su *root*
# jen can run anything on all machines except the ones
# in the "SERVERS" Host_Alias
jen ALL, !SERVERS = ALL
# jill can run any commands in the directory /usr/bin/, except for
# those in the SU and SHELLS aliases.
jill SERVERS = /usr/bin/, !SU, !SHELLS
# steve can run any command in the directory /usr/local/op_commands/
# as user operator.
steve CSNETS = (operator) /usr/local/op_commands/
# matt needs to be able to kill things on his workstation when
# they get hung.
matt valkyrie = KILL
# users in the WEBMASTERS User_Alias (will, wendy, and wim)
# may run any command as user www (which owns the web pages)
# or simply su to www.
WEBMASTERS www = (www) ALL, (root) /usr/bin/su www
# anyone can mount/unmount a cd-rom on the machines in the CDROM alias
ALL CDROM = NOPASSWD: /sbin/umount /CDROM,\
/sbin/mount -o nosuid\,nodev /dev/cd0a /CDROM
