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getty variants

mgetty, a variant of getty, supports
  1. modem dial-in,
  2. FAX, and
  3. PPP.
    4. mingetty, another a getty variant, is used for virtual consoles, or multiple login sessions at the workstation console.

getty monitors serial lines

getty monitors serial lines, waiting for a connection. It then configures the serial link, sends the contents of /etc/issue, and asks the person connecting for their login name. getty then starts login and login asks the person for their password. If the user does nothing, getty or login hang up and getty goes back to waiting. The getty command has been re-implemented numerous times.
There is a wide selection of getty clones, each with slight differences in behavior and syntax. We will describe the traditional getty, and then some popular alternatives. One of the jobs of a getty is to set the TERM environment variable to indicate the make and model of the terminal which is connecting.

Related mgetty commands

  1. mgetty: Contains the mgetty version of getty for allowing logins to Linux over serial lines.
  2. mgetty - sendfax: Contains the sendfax program for sending faxes in conjunction with the mgetty program.
  3. mgetty - viewfax: Contains the viewfax utilities for displaying faxes in X that were received by mgetty.
  4. mgetty - voice: Contains vgetty utilities for supporting voice communications with mgetty.

The six getty lines start up virtual consoles to allow logins. These processes are always running in any of the multiuser run levels. When someone connected to a virtual console logs out, that getty process dies, and the respawn action instructs init to start a new getty process.
gettydefs: Contains line definitions used by terminal devices (including modems, dumb terminals, and remote logins over terminal devices). 
pstree [-a] [-c] [-H pid] [-n] [-p] [-G] [basepid | baseuser]

Called with no arguments, pstree shows all processes, with init as the root. Specifying basepid or baseuser begins the display from the PID specified by the PID basepid or the user name baseuser, respectively. -a includes the command line for each process. -c expands identically named child processes (such as the mingetty instance spawned for each terminal). -H pid highlights the PID pid and its ancestor (parent) processes. If pid does not exist, pstree exits with an error. -n sorts the output by PID (the default is by ancestry). -p causes each process’s PID to display and implies -c. -G, finally, draws the tree using the VT100 drawing characters rather than the default ASCII characters |, +, -, and `. top displays real time CPU and memory usage and current system uptime information. Although it is an interactive command, top is a vital tool in every system administrator’s toolbox, so its command line interface (not its interactive use) is covered here.