Auto login into router running Busybox

Question

My router runs Linux with embedded Busybox. I'd like to autologin and run a web browser. Here is the /etc/inittab file:

# /etc/inittab init(8) configuration for BusyBox
#
# Copyright (C) 1999-2004 by Erik Andersen 
#
#
# Note, BusyBox init doesn't support runlevels.  The runlevels field is
# completely ignored by BusyBox init. If you want runlevels, use sysvinit.
#
#
# Format for each entry: :::
#
# : WARNING: This field has a non-traditional meaning for BusyBox init!
#
#   The id field is used by BusyBox init to specify the controlling tty for
#   the specified process to run on.  The contents of this field are
#   appended to "/dev/" and used as-is.  There is no need for this field to
#   be unique, although if it isn't you may have strange results.  If this
#   field is left blank, it is completely ignored.  Also note that if
#   BusyBox detects that a serial console is in use, then all entries
#   containing non-empty id fields will _not_ be run.  BusyBox init does
#   nothing with utmp.  We don't need no stinkin' utmp.
#
# : The runlevels field is completely ignored.
#
# : Valid actions include: sysinit, respawn, askfirst, wait, once,
#                                  restart, ctrlaltdel, and shutdown.
#
#       Note: askfirst acts just like respawn, but before running the specified
#       process it displays the line "Please press Enter to activate this
#       console." and then waits for the user to press enter before starting
#       the specified process.
#
#       Note: unrecognised actions (like initdefault) will cause init to emit
#       an error message, and then go along with its business.
#
# : Specifies the process to be executed and it's command line.
#
# Note: BusyBox init works just fine without an inittab. If no inittab is
# found, it has the following default behavior:
         ::once:/usr/sbin/usbconsole
         ::sysinit:/etc/init.d/rcS
         ::ctrlaltdel:/sbin/reboot
         ::shutdown:/etc/init.d/rc.shutdown
         ::shutdown:/sbin/swapoff -a
         ::shutdown:/bin/umount -a -r
         ::restart:/sbin/init
#
# if it detects that /dev/console is _not_ a serial console, it will
# also run:
#         tty2::askfirst:/bin/sh
#         tty3::askfirst:/bin/sh
#         tty4::askfirst:/bin/sh
#
# Boot-time system configuration/initialization script.
# This is run first except when booting in single-user mode.
#
# ::sysinit:/etc/init.d/rcS
# ::sysinit:/linuxrc

# /bin/sh invocations on selected ttys
#
# Note below that we prefix the shell commands with a "-" to indicate to the
# shell that it is supposed to be a login shell.  Normally this is handled by
# login, but since we are bypassing login in this case, BusyBox lets you do
# this yourself...
#
# Start an "askfirst" shell on the console (whatever that may be)

::askfirst:-/bin/sh

# Start an "askfirst" shell on /dev/tty2-4
# tty2::askfirst:-/bin/sh
# tty3::askfirst:-/bin/sh
# tty4::askfirst:-/bin/sh

# /sbin/getty invocations for selected ttys
# tty4::respawn:/sbin/getty 38400 tty5
# tty5::respawn:/sbin/getty 38400 tty6

# Example of how to put a getty on a serial line (for a terminal)
#::respawn:/sbin/getty -L ttyS0 115200 vt100

My router runs Linux embedded with Busybox. I'd like to autologin and run a web browser on boot. Here is the `/etc/inittab file`:
#
# Example how to put a getty on a modem line.
#::respawn:/sbin/getty 57600 ttyS2

# Stuff to do when restarting the init process
# ::restart:/sbin/init

# Stuff to do before rebooting
# ::ctrlaltdel:/sbin/reboot
# ::shutdown:/bin/umount -a -r
# ::shutdown:/sbin/swapoff -a

Answer 1

Probably a slightly late answer, but I've decided to add it anyway.

Hanging at the Cisco logo (or whatever else) is the expected behaviour in the case when the /etc/inittab file is empty. The answer depends on how you want to log into the machine. Uncommenting the line:

::respawn:/sbin/getty -L ttyS0 115200 vt100

allows you to provide login prompt on /dev/ttyS0. Assuming that you have connected over serial /dev/ttyS0 (be sure that this is in fact your interface, e.g., at my machine it is /dev/ttyPS0), the auto-login can be realised by adding:

ttyPS0::respawn:/bin/login -f <user>

This should auto log-in you as the <user>. The other approach that uses /sbin/getty and custom-made auto-login utility is described here.

If you want to automatically log-in using, e.g., /dev/tty3, you can modify the example. The auto-start of browser will depend on the X and the browser you use. I would modify the ~/.profile or ~/.bashrc in your ${HOME} directory (typically /home/<user>) by adding at the end something like:

startx
google-chrome-stable &

Note, however, that if you're connected to the router over some serial/USB cable this may not work.

Answer 2

I don't have a router to test, but at least on Buildroot + BusyBox + QEMU the following fstab entry logs you in automatically and makes everything seem to work normally:

::respawn:-/bin/sh

as I've explained at: How to login automatically without typing the root username or password in Buildroot BusyBox init?

Don't forget the leading -! Otherwise TTY interaction is a bit broken, e.g. you lose the ability to do Ctrl + C to kill the foreground program.

If you want to login as another user, you can use /bin/login as mentioned at https://unix.stackexchange.com/a/434799/32558 but you likely want to add the dash in front of it as well, for the same reason as /bin/sh:

::respawn:-/bin/login -f user0