chmod user-group-other file_name
user:所有者
group：同组者
other：其他用户
例:
"chmod 777 file_name" = "chmod rwxrwxrwx file_name" = "chmod a=rwx file_name"
"chmod 745 file_name" = "chmod rwxr--r-x file_name" = "chmod u=rwx,g=r,o=rx file_name"
r:可读
w:可写
x:可执行
rwx = 111 = 7
rw- = 110 = 6
r-x = 101 = 5
r-- = 100 = 4
-wx = 011 = 3
-w- = 010 = 2
--x = 001 = 1
--- = 000 = 0