用法：chmod [选项]… 模式[,模式]… 文件…
　或：chmod [选项]… 八进制模式 文件…
　或：chmod [选项]… --reference=参考文件 文件…
Change the mode of each FILE to MODE.
With --reference, change the mode of each FILE to that of RFILE.

-c, --changes like verbose but report only when a change is made
-f, --silent, --quiet suppress most error messages
-v, --verbose output a diagnostic for every file processed
–no-preserve-root do not treat ‘/’ specially (the default)
–preserve-root fail to operate recursively on ‘/’
–reference=RFILE use RFILE’s mode instead of MODE values
-R, --recursive change files and directories recursively
–help 显示此帮助信息并退出
–version 显示版本信息并退出

Each MODE is of the form ‘[ugoa]*(-+=)+|[-+=][0-7]+’.