Last Updated: 2022-08-06

Most commands have built-in help info, usually with the --help or -h option, e.g. $ ls --help will give you more info about the command ls.

Or open the manual by calling man, e.g. $ man ls will show the manual page of ls.

Notice that at the very beginning of the manual, the command often has a number associated with it, like LS(1), the number is the section of the manual:

  • Section 1: user commands
  • Section 2: system calls
  • Section 3: library functions
  • Section 4: special files
  • Section 5: file formats
  • Section 6: games
  • Section 7: conventions and miscellany
  • Section 8: administration and privileged commands
  • Section L: math library functions
  • Section N: tcl functions

This info can be found in the manual of manual: $ man man.

The same entry may appear in different sections, e.g. to check manual for mount in system calls vs admin command:

$ man 2 mount # the system call
$ man 8 mount # the admin command

Use man -k to search the man pages, e.g. $ man -k mount will not only return mount but also umount, cgroupfs-mount, etc. This is equivalent to apropos mount

Use man -f to list all sections that have the term.

$ man -f mount
mount (8)            - mount a filesystem
mount (2)            - mount filesystem