Yocdroid is a Linux userspace environment for use on Android devices
based on the Yocto Linux Project's distribution build system.

With it, you can have a (more or less) fully integratied "real" Linux
command line environment on your Android machine without losing the
ability to interoperate with the core Android world.  For example:

+ It's linux: bash, perl, python, ssh, curl, wget.  Cron jobs!  Use
  "file" on unknown data.

+ Android stuff works like you expect: "getprop ro.whatever", "pm
  install something.apk", "am start ...".  Script activity and intent
  management using robust tools.

+ Find your device on any local network via Avahi/Zeroconf
  ("avahi-browse -a", "ssh andyphone.local").  Android as of 4.2 still
  lacks a mDNS responder running by default.

+ Terminals spawned from ssh instead of adb understand SIGWINCH and
  get proper settings for LINES/COLUMNS.  No more broken terminal
  output.

+ Run lspci/lsusb to get human-readable output (on devices with PCI or
  USB host buses, of course).

+ Run acpid/acpi_listen to inspect firmware events (likewise on
  compatible hardware).

+ netstat, iptables, tcpdump, iwconfig/iwlist (for compatible hardware)

+ Attach a local gdb to an android process.  This is tons eaiser than
  messing with gdbserver and for simple debugging just as good (you
  will need to have unstripped libraries in /system/lib to get source
  info in the backtrace, of course).  It even works with Bionic
  pthreads!

+ Mount the android filesystem locally via sshfs.  Mount remote
  filesystems on the Android box over sshfs.  Edit files on the
  Android box over ssh using TRAMP mode in emacs or equivalent.

+ Run a persistent screen session on your device for long-running
  console tools.