创建1个新目录他的硬连接数是2，为何？

它本身 和目录名..

[root@oldboyedu59 ~]# ll -di  /lidao/ /lidao/.
67141566 drwxr-xr-x. 2 root root 24 Mar 29 09:08 /lidao/
67141566 drwxr-xr-x. 2 root root 24 Mar 29 09:08 /lidao/.

#在这个目录下面创建1个新目录 /lidao/alex/  lidao目录的硬链接数是几？ 3
[root@oldboyedu59 ~]# ll -di  /lidao/  /lidao/.  /lidao/alex/..
67141566 drwxr-xr-x. 3 root root 36 Apr 11 09:08 /lidao/
67141566 drwxr-xr-x. 3 root root 36 Apr 11 09:08 /lidao/.
67141566 drwxr-xr-x. 3 root root 36 Apr 11 09:08 /lidao/alex/..

我是谁

[root@handsome-man ~]# whoami
root
[root@handsome-man ~]# 

查询id

[root@handsome-man ~]# id
uid=0(root) gid=0(root) groups=0(root)
[root@handsome-man ~]# 

#添加用户
[root@oldboyedu59 ~]# useradd oldboy 
[root@oldboyedu59 ~]# id oldboy 
uid=1000(oldboy) gid=1000(oldboy) groups=1000(oldboy)

设置密码

[root@oldboyedu59 ~]# passwd  oldboy
Changing password for user oldboy.
New password: 
BAD PASSWORD: The password is shorter than 8 characters
Retype new password: 
passwd: all authentication tokens updated successfully.

切换用户

[root@oldboyedu59 ~]# su  -  oldboy 
[oldboy@oldboyedu59 ~]$ whoami 
oldboy
[oldboy@oldboyedu59 ~]$ id
uid=1000(oldboy) gid=1000(oldboy) groups=1000(oldboy)


[root@oldboyedu59 ~]# ls -l /etc/passwd  /etc/shadow
-rw-r--r-- 1 root root 1017 Apr 11 09:29 /etc/passwd
---------- 1 root root  746 Apr 11 09:42 /etc/shadow

查找用户

cat /etc/passwd

删除用户

userdel +用户名

文件权限

xx xx59 老王 xxav.macbook

主人 家人 外人（陌生人）
所有者 所属用户组 其他人（陌生人）
user group other
u g o

oldboy用户

rwx
r 4 read 是否可以读
w 2 write 是否可以写
x 1 executable 是否可以运行（执行）
运行命令
运行脚本
- 0

都是三个为一组

[root@oldboyedu59 oldboy]# ls -l /etc/hosts  /bin/ls 
-rwxr-xr-x. 1 root root 117680 Oct 31 03:16 /bin/ls
-rw-r--r--  1 root root    188 Apr  1 17:13 /etc/hosts

根据字母推出数字权限

-rwxr-xr-x
 421401401
 7  5  5 

 
-rw-r--r-- 
 420400400
 6  4  4 

根据数字推出字母权限

750 rwx r-x ---
640 rw- r-- ---
604 rw- --- r--
644 rw- r-- r--
400 r-- --- ---

根据数字形式 修改权限

[root@oldboyedu59 oldboy]# ls -l oldboy.txt
-rw-r--r-- 2 root root 7 Apr 10 11:57 oldboy.txt
[root@oldboyedu59 oldboy]# chmod 755 oldboy.txt
[root@oldboyedu59 oldboy]# ls -l oldboy.txt
-rwxr-xr-x 2 root root 7 Apr 10 11:57 oldboy.txt

根据字符形式 修改权限

[root@oldboyedu59 oldboy]# chmod u-w oldboy.txt
[root@oldboyedu59 oldboy]# ll  oldboy.txt
-r--r--r-- 2 root root 7 Apr 10 11:57 oldboy.txt
[root@oldboyedu59 oldboy]# chmod u+w oldboy.txt
[root@oldboyedu59 oldboy]# ll oldboy.txt
-rw-r--r-- 2 root root 7 Apr 10 11:57 oldboy.txt
[root@oldboyedu59 oldboy]# chmod u=w oldboy.txt
[root@oldboyedu59 oldboy]# ll oldboy.txt
--w-r--r-- 2 root root 7 Apr 10 11:57 oldboy.txt

把oldboy.txt的文件修改为644

给oldboy.txt ugo每个位置都增加上执行权限
[root@oldboyedu59 oldboy]# chmod ugo+x oldboy.txt
[root@oldboyedu59 oldboy]# chmod a-x oldboy.txt
[root@oldboyedu59 oldboy]# 
[root@oldboyedu59 oldboy]# ll oldboy.txt
-rw-r--r-- 2 root root 7 Apr 10 11:57 oldboy.txt
[root@oldboyedu59 oldboy]# chmod a+x oldboy.txt
[root@oldboyedu59 oldboy]# ll oldboy.txt
-rwxr-xr-x 2 root root 7 Apr 10 11:57 oldboy.txt
[root@oldboyedu59 oldboy]# chmod  a-x oldboy.txt
[root@oldboyedu59 oldboy]# ll oldboy.txt
-rw-r--r-- 2 root root 7 Apr 10 11:57 oldboy.txt
[root@oldboyedu59 oldboy]# chmod +x oldboy.txt
[root@oldboyedu59 oldboy]# ll oldboy.txt
-rwxr-xr-x 2 root root 7 Apr 10 11:57 oldboy.txt

[root@oldboyedu59 ~]# ll /etc/rc.local 
lrwxrwxrwx. 1 root root 13 Mar 26 11:39 /etc/rc.local -> rc.d/rc.local
[root@oldboyedu59 ~]# ll /etc/rc.d/rc.local 
-rw-r--r--. 1 root root 473 Oct 31 07:31 /etc/rc.d/rc.local
[root@oldboyedu59 ~]# chmod +x /etc/rc.d/rc.local
[root@oldboyedu59 ~]# ll /etc/rc.d/rc.local
-rwxr-xr-x. 1 root root 473 Oct 31 07:31 /etc/rc.d/rc.local

chmod ugo+x oldboy.txt
chmod a+x oldboy.txt

chmod +x oldboy.txt √√√√√√

chmod ugo +|-|= oldboy.txt
chmod u=rw,g=r,o=rx oldboy.txt

[面试题]文件属性(inode-软硬链接-用户-权限）
https://www.jianshu.com/p/5b83985768e7