比如
man ls，显示为LS(1)
man fread，显示为FREAD(3)
这其实是代表对应的命令在man中的章节号，具体编号如下：
1. General commands
2. System calls
3. C library functions
4. Special files (usually devices, those found in /dev) and drivers
5. File formats and conventions
6. Games and screensavers
7. Miscellanea
8. System administration commands and daemons
阅读：10