一、 su命令
1.切换用户su - fxq
su命令后带"- ",表示环境变量一起切换过去
[root@VM_46_188_centos ~]# whoami root [root@VM_46_188_centos ~]# Last login: Tue Aug 8 22:30:12 CST 2017 on pts/0 [fxq@VM_46_188_centos ~]$ pwd /home/fxq [fxq@VM_46_188_centos ~]$ su Password: [root@VM_46_188_centos fxq]# pwd/home/fxq [root@VM_46_188_centos fxq]# cd [root@VM_46_188_centos ~]# [fxq@VM_46_188_centos root]$ pwd /root [fxq@VM_46_188_centos root]$
2. root 以user2身份执行命令：
su - -c "touch /tmp/user2.txt" user2
[fxq@VM_46_188_centos root]$ su - -c "touch /tmp/user2.txt" user2 Password: [fxq@VM_46_188_centos root]$ exit [root@VM_46_188_centos ~]# su - -c "touch /tmp/user2.txt" user2 [root@VM_46_188_centos ~]# ls -l /tmptotal 200-rw-r--r-- 1 root root 238 Aug 8 15:15 1.txt -rwxr--r-- 1 root root 0 Aug 7 22:25 2.txt -rwxr-xr-x 1 root root 743 Jul 5 17:13 aliyun-yum-install.sh drwxr-xr-x 4 root root 4096 Aug 6 21:32 fxq -rw-r--r-- 1 root root 486 Aug 13 05:00 ls.log1 -rwxr-xr-x 1 root root 117616 Aug 6 21:09 ls2 -rw-r--r-- 1 root root 1742 Aug 6 21:20 passwd -rw-r--r-- 1 root root 1742 Aug 6 21:27 passwd2 -rw------- 1 daemon daemon 33 Aug 13 14:36 sess_1b99a57326be2b43a e545ca31df73d40 -rw------- 1 daemon daemon 33 Aug 13 03:18 sess_2cc7b36f29dd4273f c82a383b7e05593 -rw------- 1 daemon daemon 33 Aug 13 14:36 sess_2e809bf78820261ef35e4004dbc8aa9f -rw------- 1 daemon daemon 33 Aug 13 23:27 sess_a5aa9fa1bd0986f8f968e1283c28bf08 -rw-rw-r-- 1 user2 user2 0 Aug 13 23:30 user2.txt [root@VM_46_188_centos ~]#
3. 系统中环境变量文件备用文件存储位置
ls -la /etc/skel/ 里面有环境变量文件
如果用户家目录中没有环境变量文件可以从些文件夹中copy。然后改变对应用户的所属主和所属组.
[root@VM_46_188_centos ~]# ls -la /etc/skel/total 28drwxr-xr-x. 2 root root 4096 Nov 10 2016 . drwxr-xr-x. 95 root root 12288 Aug 13 23:33 .. -rw-r--r-- 1 root root 18 Aug 3 2016 .bash_logout -rw-r--r-- 1 root root 193 Aug 3 2016 .bash_profile -rw-r--r-- 1 root root 231 Aug 3 2016 .bashrc [root@VM_46_188_centos ~]#
模拟环境变量文件丢失后恢复：
[root@VM_46_188_centos skel]# rm -rf /home/user111/.bash* [root@VM_46_188_centos skel]# ls -la /home/user111/ total 8 drwx------ 2 user111 user111 4096 Aug 13 23:42 . drwxr-xr-x. 17 root root 4096 Aug 13 23:33 .. [root@VM_46_188_centos skel]# su - user111 Last login: Sun Aug 13 23:38:18 CST 2017 on pts/0-bash-4.2$ -bash-4.2$ -bash-4.2$ pwd /home/user111 -bash-4.2$ logout [root@VM_46_188_centos skel]# pwd/etc/skel [root@VM_46_188_centos skel]# ls -a. .. .bash_logout .bash_profile .bashrc [root@VM_46_188_centos skel]# cp .bash* /home/user111/ [root@VM_46_188_centos skel]# ls -a /home/user111/ . .. .bash_history .bash_logout .bash_profile .bashrc [root@VM_46_188_centos skel]# su - user111 Last login: Sun Aug 13 23:42:58 CST 2017 on pts/0 [user111@VM_46_188_centos ~]$ [user111@VM_46_188_centos ~]$ pwd /home/user111 [user111@VM_46_188_centos ~]$
二、 sudo命令
1. visudo 打开sudo的配置文件
vi /etc/sudoers.tmp 编辑完没有语法错误提示
## The COMMANDS section may have other options added to it.#### Allow root to run any commands anywhere root ALL=(ALL) ALL
vi 中显示行号: "set nu"
[fxq@VM_46_188_centos ~]$ ls /root ls: cannot open directory /root: Permission denied [fxq@VM_46_188_centos ~]$ sudo ls /root [sudo] password for fxq: #fxq.txt 123.zip gdlogo.png, 2 gdlogo.png.1,.pub 2.cap gdlogo.png.hard1 22.txt gdlogo.png.soft1.cap 234 httpd_process_check.sh1.ipt 3.txt ip.txt1.log.tar 4.txt iptables.rules1.log.tar.bz2 [1-3].log null1.log.tar.gz \fxq.txt ping_host_alive.sh1.log.tar1.xz a.out sed.txt1.log.xz anaconda-ks.cfg shell1.log.zip auto_install_lamp.sh testOS.xsh1.txt baidu.png weixin111.txt dir-2017-05-12 wordpress-4.7.4-zh_CN.zip11111111 ffff youjian.sh12 fxq ~iptables_rules123 fxq-0.xsh [fxq@VM_46_188_centos ~]$
[fxq@VM_46_188_centos ~]$ ls /root ls: cannot open directory /root: Permission denied [fxq@VM_46_188_centos ~]$ sudo ls /root #fxq.txt 123.zip gdlogo.png, 2 gdlogo.png.1,.pub 2.cap gdlogo.png.hard1 22.txt gdlogo.png.soft1.cap 234 httpd_process_check.sh1.ipt 3.txt ip.txt1.log.tar 4.txt iptables.rules1.log.tar.bz2 [1-3].log null1.log.tar.gz \fxq.txt ping_host_alive.sh1.log.tar1.xz a.out sed.txt1.log.xz anaconda-ks.cfg shell1.log.zip auto_install_lamp.sh testOS.xsh1.txt baidu.png weixin111.txt dir-2017-05-12 wordpress-4.7.4-zh_CN.zip11111111 ffff youjian.sh12 fxq ~iptables_rules123 fxq-0.xsh [fxq@VM_46_188_centos ~]$
2. 用户sudo时不用输入密码:
## The COMMANDS section may have other options added to it. #### Allow root to run any commands anywhere root ALL=(ALL) ALL
# # 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
三、 限制root远程登录
1. 建立用户组
# # 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, mikemUser_Alias ADMINS = fxq,user111
2. 切换用户时不需要输入密码
## user MACHINE=COMMANDS#### The COMMANDS section may have other options added to it.#### Allow root to run any commands anywhereroot ALL=(ALL) ALLADMINS ALL=(ALL) NOPASSWD: /usr/bin/su
3. 限制root用户远程登录
（1）编辑配置文件：
vi /etc/ssh/sshd_config
#LoginGraceTime 2m PermitRootLogin no#StrictModes yes#MaxAuthTries 6#MaxSessions 10
（2）重启sshd服务
systemctl restart sshd
更改完配置文件后，重启sshd服务，测试root确实无法登录:
(3) 测试root用户远程登录
远程无法登录root，可以通过刚才做的普通用户su - 进入root用户.
@VM_46_188_centos ~]$ [fxq@VM_46_188_centos ~]$ [fxq@VM_46_188_centos ~]$ [fxq@VM_46_188_centos ~]$ sudo su - Last login: Mon Aug 14 00:12:59 CST 2017 on pts/0 Last failed login: Mon Aug 14 00:18:33 CST 2017 from 60.10.158.223 on ssh:nottyThere was 1 failed login attempt since the last successful login. [@VM_46_188_centos ~]# [root@VM_46_188_centos ~]#
四、扩展
1. sudo与su比较 http://www.apelearn.com/bbs/thread-7467-1-1.html
su 和 sudo 命令的区别
su命令就是临时切换用户的工具,su 加参数 -，表示默认切换到root用户，并且改变到root用户的环境；su只适用于一两个人参与管理的系统,多人管理的话不安全。
sudo 授权许可使用的su，也是受限制的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；
2. sudo配置文件样例 www.opensource.apple.com/source/sudo/sudo-16/sudo/sample.sudoers
# # 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/killCmnd_Alias PRINTING = /usr/sbin/lpc, /usr/bin/lprm Cmnd_Alias SHUTDOWN = /usr/sbin/shutdownCmnd_Alias HALT = /usr/sbin/halt Cmnd_Alias REBOOT = /usr/sbin/reboot Cmnd_Alias SHELLS = /sbin/sh, /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=authDefaults>root !set_lognameDefaults:FULLTIMERS !lectureDefaults:millert !authenticateDefaults@SERVERS log_year, logfile=/var/log/sudo.log## # User specification ## # root and users in group wheel can run anything on any machine as any userroot ALL = (ALL) ALL %wheel ALL = (ALL) ALL # full time sysadmins can run anything on any machine without a passwordFULLTIMERS ALL = NOPASSWD: ALL # part time sysadmins may run anything but need a passwordPARTTIMERS 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, SHUTDOWN, HALT, REBOOT, PRINTING,\ sudoedit /etc/printcap, /usr/oper/bin/ # joe may su only to operatorjoe 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 passwordfred 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 aliasALL CDROM = NOPASSWD: /sbin/umount /CDROM,\ /sbin/mount -o nosuid\,nodev /dev/cd0a /CDROM
3. sudo -i 也可以登录到root吗？ http://www.apelearn.com/bbs/thread-6899-1-1.html
sudo -i: 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，可以使用该命令。提示输入密码时该密码为当前账户的密码。没有时间限制。执行该命令后提示符变为“#”而不是“$”。想退回普通账户时可以执行“exit”或“logout” 。 其实，还有几个类似的用法： sudo /bin/bash ： 这个命令也会切换到root的bash下，但不能完全拥有root的所有环境变量，比如PATH，可以拥有root用户的权限。这个命令和 sudo -s 是等同的。 sudo -s : 如上 sudo su ： 这个命令，也是登录到了root，但是并没有切换root的环境变量，比如PATH。 sudo su - : 这个命令，纯粹的切换到root环境下，可以这样理解，先是切换到了root身份，然后又以root身份执行了 su - ，这个时候跟使用root登录没有什么区别。这个结果貌似跟sudo -i 的效果是一样的，但是也有不同，sudo 只是临时拥有了root的权限，而su则是使用root账号登录了linux系统。 所以，我们再来总结一下： sudo su - 约等于 sudo -i sudo -s 完全等于 sudo /bin/bash 约等于 sudo su sudo 终究被一个"临时权限的帽子"扣住，不能等价于纯粹的登录到系统里。
本文转自 枫叶云 51CTO博客，原文链接:http://blog.51cto.com/fengyunshan911/1957181
