man

  1. Executable programs or shell commands
  2. System calls (functions provided by the kernel)
  3. Library calls (functions within program libraries)
  4. Special files (usually found in /dev)
  5. File formats and conventions eg /etc/passwd
  6. Games
  7. Miscellaneous (including macro packages and conventions), e.g. man(7), groff(7)
  8. System administration commands (usually only for root)
  9. Kernel routines [Non standard]
1
2
3
4
5
6
$ ls /usr/bin/passwd /etc/passwd
/etc/passwd  /usr/bin/passwd

$ man 1 passwd
$ man 5 passwd
$ man -a passwd

help

  1. shell（命令解析器）自带的命令称为内部命令，其它的是外部命令
  2. 内部命令：help cd
  3. 外部命令：ls --help
1
2
3
4
5
$ type cd
cd is a shell builtin

$ type ls
ls is aliased to `ls --color=auto'

info

  1. info比help更详细，info ls

参考资料

Linux实战技能100讲