Gotty
Gotty is a getty framework based on letty. The difference to classical gettys is, that it is not a single program but a pluggable set of tools. Whenever you need alternative functionality or additional features just implement them and reuse the rest. Thus you get a highly configurable getty without complex configuration files and huge binaries.
Commands
Gotty provides multiple basic tools:
| name | usage | description |
|---|---|---|
| g-init | g-init [-c,--clear] <tty path> </path/program arguments> | initializes the tty given by <tty path> and optionally clears its content |
| g-utmp | g-utmp </path/program arguments> | updates the utmp/wtmp file entries for the current PID and the terminal associated with stdin |
| g-env | g-env <TERM-value> </path/program arguments> | sets the environment variables TERM to <TERM-value> and TTY to the terminal associated with stdin |
| g-out | g-out <text> [/path/program arguments] | writes <text> to stdout |
| g-re | g-re [/path/program arguments] | reads up to GOTTY_LOGIN_NAME_MAX characters from stdin, checks if these characters are in the portable filename character set and optionally executes </path/program ... input> with the character string as last argument |
| g-out-v (optional) | g-out-v <text> [/path/program arguments] | it writes <text> to stdout as well as g-out but prepends: This is <nodename> (<machine>-<sysname>-<release>). |
| g-r (optional) | g-r </path/program arguments> | Both programs together reimplement g-re. G-r is an IA32 assembler program which reads a string and executes g-ve to validate the input. |
| g-ve (optional) | g-ve <text> [/path/program arguments] |
The last three are examples of possible customizations. Common to all commands is the <mandatory> or [optional] execution of another command to build up the functionality of a getty.
Configuration
Configure via macros or Makefile.
| name | Makefile | default | description | commands |
|---|---|---|---|---|
| GOTTY_LOGIN_NAME_MAX | getconf LOGIN_NAME_MAX | 256 | maximium login name length | g-re, g-r, g-ve |
| GOTTY_UTMPX_USER | "LOGIN" | "LOGIN" | ut_user in utmpx entry | g-utmp |
| GOTTY_WTMP_PATH | /var/log/wtmp | /var/log/wtmp | path to wtmp file | g-utmp |
| GOTTY_CLEAR_SEQUENCE | "\033c" | "\033c" | terminal clear sequence | g-init |
| GOTTY_USE_UPDWTMP | 0 | 0 | use libc' updwtmp() | g-utmp |
Installation
A simple make, make install is enough after customizing the Makefile. For the optional programs execute make <name> before the installation step.
Usage
Gettys are usually invoked by init(8) and hence the configuration depends on the init system. A common way is to edit /etc/inittab.
A basic getty:
c2:2345:respawn:/sbin/g-init /dev/tty2 /sbin/g-out "login: " /sbin/g-re /bin/login
A verbose getty which clears the screen, updates utmp and sets environment variables:
c2:2345:respawn:/sbin/g-init -c /dev/tty2 /sbin/g-utmp /sbin/g-env linux /sbin/g-out-v "login: " /sbin/g-re /bin/login
Maybe you prefer the 182B assembler version waiting for input:
c2:2345:respawn:/sbin/g-init -c /dev/tty2 /sbin/g-out-v "login: " /sbin/g-r /sbin/g-ve /bin/login
or autologin?
c2:2345:respawn:/sbin/g-init -c /dev/tty2 /sbin/g-utmp /bin/login -f <username>
Please test your configuration with kill -HUP 1 before restarting.
Standards
Apart from g-r and g-init, all programs conform to C99 and POSIX.1-2008. G-r was written in IA32 Assembler (Intel syntax) and g-init uses non-Posix functions like vhangup().
Compilers and Libraries
Gotty was tested with multiple C libraries (dietlibc 0.33, musl 0.9.3 (no utmpx support), glibc 2.15) and compilers (clang 2.9, CompCert 1.11, gcc 4.5.3). The binary sizes (statically linked) on the test system were:
| command | diet gcc | musl-gcc | nasm/yasm |
|---|---|---|---|
| g-init | 3092B | 4740B | |
| g-utmp | 5036B | 17032B | |
| g-env | 4612B | 21124B | |
| g-out | 2172B | 4740B | |
| g-re | 2364B | 4740B | |
| g-out-v | 2400B | 4740B | |
| g-r | 182B | ||
| g-ve | 2348B | 4740B |