Posix Shell and Terminal [DRAFT]
Created at 2017-04-05T22:23:23+09:00

My understanding of terminal and shell after reading POSIX.1-2008.

Especially around:

Definitions

  • Concepts not specific to shell
    • terminal (def. A character special file that obeys the specifications of the general terminal interface.)
    • session
    • session leader
    • process group
    • process
    • controlling terminal
    • controlling process
    • connection (from process to terminal)

Hierarchical view:

session (created upon `setsid`)
'-' session leader
    (extends process)
    (will be called controlling process if it's establishing connection to the controlling terminal)
'-* process group (created upon `setpgid`) (a.k.a. job)
  '-' process group leader (extends process)
  '-* process
'?' controlling terminal (it's optional)

foreground process group (extends process group) (set upon `tcsetpgrp`)
background process group (extends process group)
  • Shell

  • Terminal

    • input control: (11.1.5 Input Processing and Reading Data)
      • so, Kernel (or tty subsystem) is supposed to implement something like Ctrl-C to SIGINT signal logic.
    • output control:

  • Things left to implementation

    • "The controlling terminal for a session is allocated by the session leader in an implementation-defined manner."
      • so, we have to look at agetty or gnome-terminal for example?

Real World Example

which I have to read and understand.

  • /dev/console
  • /dev/tty(n)
  • /dev/pts/(n)
  • gnome-terminal
  • zsh
  • getty
  • Xorg
  • PID1

Side Notes

  • how to check controlling process group (forground job) ?
  • PID1's stdin/stdout/stderr
  • Seat
  • Graphical session

Reference