Poky-Tiny
Poky-tiny is a variant of the poky distribution which is stripped down to minimal configuration.
Introduction
It is intended to be useful for a few different purposes:
- as a demonstration of techniques useful for reducing other images
- as a springboard for very low-end distributions and images
- as a place to experiment with whole-system optimization techniques
It was written by Darren Hart.
Basic use
To use the poky-tiny distro, adjust the DISTRO setting in your conf/local.conf file. That is, set it to: "DISTRO=poky-tiny"
poky-tiny does not include a target-side package manager, so it is useful, to avoid extra dependencies, to use it with the IPKG package management scheme. This is the lightest-weight package management scheme. Set this in your conf/local.conf file:
PACKAGE_CLASSES ?= "package_ipk"
Then do a basic build of the system:
$ bitbake core-image-minimal
Resulting images should appear in your <build-dir>/tmp/deploy/images directory.
FAQ
- where is poky-tiny defined?
- poky-tiny is defined in <yocto-dir>/meta-yocto/conf/distro/poky-tiny.conf. Some other recipes and images have been modified to support the features in poky-tiny.
- The kernel recipe for poky-tiny is in <yocto-dir>/meta/recipes-kernel/linux/linux-yocto-tiny_x.x.bb
- What images are supported?
- As of poky-danny-8.0 (the 1.3 release of yocto), poky-tiny.conf defined the following images: IMAGE_FSTYPES = "ext2 cpio.gz" This means it will build both an ext2 filesystem image, and a cpio.gz image (suitable for use as an initramfs).
- What machines are supported (are there any restrictions)?
- in the kernel recipe file, it has COMPATIBLE_MACHINE="(qemux86)"
- What features have been eliminated?
- What is the size difference between poky-tiny and poky (core-image-minimal)?
- Are there differences in the way poky-tiny is customized, from the way default 'poky' is customized? (eg. gotchas for adding to IMAGE_INSTALL or IMAGE_FEATURES)?
Creating your own tiny-based distro
You can create your own distro, based on the tiny work, by copying the poky-tiny.conf file to your own layer, and editing it from there.
Assuming you are calling your layer 'meta-foo', you could do the following:
- create your meta-foo layer (see other docs for this)
- copy the poky-tiny distro configuration file to your own layer
$ install -p meta-foo/conf/distro $ cp meta-yocto/conf/distro/poky-tiny.conf meta-foo/conf/distro/foo-tiny.conf
- edit your conf/local.conf to use your foo-tiny.conf distro
$ vi <build-dir>/conf/local.conf [change it so "DISTRO?=foo-tiny"]
Adjusting poky-tiny
Controlling LIBC features
Inside foo-tiny.conf (derived from poky-tiny.conf), you can specify what LIBC features to support by modifying the DISTRO_FEATURES_LIBC variable.
This variable is declared to be a space-separated list of other DISTRO_FEATURES_LIBC_xxx variables. To turn on or off features in libc, edit the values of these variables.
eglibc
To see different options that are available, see the file: <yocto-dir>/meta/recipes-core/eglibc/eglibc-options.inc
Listed in that file are the routines: distro_features_check_deps() and features_to_eglibc_settings(), which map items listed in DISTRO_FEATURES_LIBC into specific eglibc settings.
uclibc
To see different options that are available, see the file: <yocto-dir>/meta/recipes-core/uclibc/uclibc-config.inc
Listed in that file is the routine: features_to_uclibc_settings(), which maps items listed in DISTRO_FEATURES_LIBC into specific uclibc settings.
Controlling kernel features
Controlling busybox features
Troubleshooting the build
Invoking qemu with poky-tiny images
Runqemu doesn't understand poky-tiny (or initramfs?). Try executing qemu directly instead. Here's the template:
$ qemu-system-i386 -kernel path/to/kernel -initrd path/to/image.cpio.gz -nographic -append "console=ttyS0 root=/dev/ram0"
Here the actual full command I used:
$ tmp/sysroots/x86_64-linux/usr/bin/qemu-system-i386 -kernel tmp/deploy/images/bzImage-qemux86.bin -initrd tmp/deploy/images/core-image-minimal-qemux86.cpio.gz -nographic -append "console=ttyS0 root=/dev/ram0"
Some information about the running system
You can poke around, and see the status of various things. 'ps' shows only 22 processes running, with only 3 user-space (ie not kernel threads):
# ps | grep -v [[]
PID USER VSZ STAT COMMAND
1 root 2004 S {init} /bin/sh /init
38 root 2144 S sh
41 root 2144 R ps
So... busybox is really the only executable on the system, and it is providing /bin/sh. /init is a shell script, which will run /etc/rc.local, if one is present. There's a sample in /etc/rc.local.sample that you can use as a starting point to customize the init process. If you turn on packages in yocto, there will be init scripts deposited in /etc/init.d, which you can call from either /init or /etc/rc.local to invoke (none of that fancy sysV rc init scripts here!)
I booted with mem=24M (that was about as small as I could go) and saw the following memory utilization:
# free
total used free shared buffers
Mem: 19724 5944 13780 0 0
-/+ buffers: 5944 13780
Swap: 0 0 0
The filesystem is a little over 3M in size:
# du -sh / 3.2M /
Here's a sample of what the filesystem looks like (as of yocto-danny-8.0), with results sorted by size and /sys, /proc and /dev omitted:
# find / -type f -xdev | xargs ls -laSr -rw-r--r-- 1 root root 0 Nov 14 21:24 /lib/modules/3.4.11-yocto-tiny/modules.dep -rw-r--r-- 1 root root 0 Nov 14 21:24 /lib/modules/3.4.11-yocto-tiny/modules.builtin.bin -rw-r--r-- 1 root root 0 Nov 14 00:45 /etc/network/nm-disabled-eth0 -rw-r--r-- 1 root root 0 Nov 14 00:45 /etc/motd -rw-r--r-- 1 root root 0 Nov 14 00:14 /etc/ld.so.conf -rw-r--r-- 1 root root 0 Nov 14 00:45 /etc/default/usbd -rw-r--r-- 1 root root 6 Nov 14 22:05 /var/volatile/run/ifstate -rw-r--r-- 1 root root 8 Nov 14 00:45 /etc/hostname -rw-r--r-- 1 root root 12 Nov 14 21:24 /lib/modules/3.4.11-yocto-tiny/modules.symbols.bin -rw-r--r-- 1 root root 12 Nov 14 21:24 /lib/modules/3.4.11-yocto-tiny/modules.dep.bin -rw-r--r-- 1 root root 12 Nov 14 21:24 /lib/modules/3.4.11-yocto-tiny/modules.alias.bin -rw-r--r-- 1 root root 13 Nov 14 21:24 /etc/version -rw-r--r-- 1 root root 13 Nov 14 21:24 /etc/timestamp -rw-r--r-- 1 root root 26 Nov 14 00:45 /etc/host.conf -rw-r--r-- 1 root root 38 Nov 14 00:45 /etc/filesystems -rw-r--r-- 1 root root 44 Nov 14 00:45 /etc/hosts -rw-r--r-- 1 root root 45 Nov 14 21:24 /lib/modules/3.4.11-yocto-tiny/modules.alias -rwxr-xr-x 1 root root 49 Nov 14 00:22 /usr/share/udhcpc/default.script -rw-r--r-- 1 root root 49 Nov 14 21:24 /lib/modules/3.4.11-yocto-tiny/modules.symbols -rw-r--r-- 1 root root 52 Nov 14 21:24 /lib/modules/3.4.11-yocto-tiny/modules.devname -rw-r--r-- 1 root root 72 Nov 14 00:45 /etc/issue.net -rw-r--r-- 1 root root 74 Nov 14 00:45 /etc/issue -rwxr-xr-x 1 root root 93 Nov 13 20:19 /etc/default/devpts -rw-r--r-- 1 root root 109 Nov 14 00:45 /etc/shells -rw-r--r-- 1 root root 131 Nov 14 21:24 /lib/modules/3.4.11-yocto-tiny/modules.softdep -rw-r--r-- 1 root root 132 Nov 14 00:45 /etc/network/interfaces -rwxr-xr-x 1 root root 152 Nov 14 00:45 /etc/skel/.profile -rwxr-xr-x 1 root root 270 Nov 13 20:19 /etc/init.d/hostname.sh -rwxr-xr-x 1 root root 289 Nov 13 20:19 /etc/init.d/reboot -rwxr-xr-x 1 root root 321 Nov 13 20:19 /etc/init.d/save-rtc.sh -rwxr-xr-x 1 root root 410 Nov 14 00:45 /etc/skel/.bashrc -rwxr-xr-x 1 root root 438 Nov 13 20:19 /etc/init.d/sendsigs -rw-r--r-- 1 root root 446 Nov 14 21:23 /etc/group -rw-r--r-- 1 root root 465 Nov 14 00:45 /etc/nsswitch.conf -rwxr-xr-x 1 root root 473 Nov 14 21:24 /init -rwxr-xr-x 1 root root 492 Nov 13 20:19 /etc/init.d/banner.sh -rwxr-xr-x 1 root root 510 Nov 13 20:19 /etc/init.d/halt -rwxr-xr-x 1 root root 516 Nov 13 20:19 /etc/init.d/umountfs -rwxr-xr-x 1 root root 526 Nov 13 20:19 /etc/init.d/devpts.sh -rwxr-xr-x 1 root root 578 Nov 13 20:19 /etc/init.d/single -rwxr-xr-x 1 root root 585 Nov 13 20:19 /etc/init.d/rmnologin.sh -rw-r--r-- 1 root root 586 Nov 14 00:20 /usr/share/run-postinsts/run-postinsts.awk -rwxr-xr-x 1 root root 609 Nov 14 00:20 /etc/init.d/run-postinsts -rwxr-xr-x 1 root root 632 Nov 14 00:45 /etc/rc.local.sample -rw-r--r-- 1 root root 651 Nov 14 00:22 /etc/syslog-startup.conf.busybox -rwxr-xr-x 1 root root 660 Nov 13 20:19 /etc/init.d/sysfs.sh -rw-r--r-- 1 root root 704 Nov 14 00:45 /etc/fstab -rwxr-xr-x 1 root root 711 Nov 13 20:19 /etc/init.d/umountnfs.sh -rw-r--r-- 1 root root 719 Nov 14 21:23 /etc/passwd -rw------- 1 root root 737 Nov 14 22:22 /.ash_history -rw-r--r-- 1 root root 783 Nov 14 21:24 /etc/ld.so.cache -rwxr-xr-x 1 root root 809 Nov 14 00:45 /etc/network/if-pre-up.d/nfsroot -rw------- 1 root root 836 Nov 14 21:24 /var/volatile/cache/ldconfig/aux-cache -rw-r--r-- 1 root root 847 Nov 14 00:45 /etc/profile -rwxr-xr-x 1 root root 859 Nov 13 20:19 /etc/init.d/mountall.sh -rwxr-xr-x 1 root root 878 Nov 14 00:45 /etc/init.d/modutils.sh -rw-r--r-- 1 root root 887 Nov 14 00:45 /etc/rpc -rw-r--r-- 1 root root 1123 Nov 13 20:19 /etc/init.d/functions.initscripts -rwxr-xr-x 1 root root 1349 Nov 13 20:19 /etc/init.d/urandom -rwxr-xr-x 1 root root 1540 Nov 13 20:19 /etc/init.d/mountnfs.sh -rw-r--r-- 1 root root 1633 Nov 14 00:45 /etc/inputrc -rwxr-xr-x 1 root root 1711 Nov 14 00:22 /etc/init.d/syslog.busybox -rw-r--r-- 1 root root 1740 Nov 13 20:19 /etc/default/volatiles/00_core -rwxr-xr-x 1 root root 1752 Nov 13 20:19 /etc/init.d/bootmisc.sh -rwxr-xr-x 1 root root 1909 Nov 14 00:45 /etc/init.d/networking -rw-r--r-- 1 root root 2146 Nov 14 00:22 /etc/busybox.links -rwxr-xr-x 1 root root 2514 Nov 14 00:22 /etc/init.d/hwclock.sh -rwxr-xr-x 1 root root 2548 Nov 14 00:22 /etc/udhcpc.d/50default -rw-r--r-- 1 root root 2933 Nov 14 00:45 /etc/protocols -rwxr-xr-x 1 root root 3229 Nov 13 20:19 /etc/init.d/checkroot.sh -rwxr-xr-x 1 root root 4409 Nov 13 20:16 /usr/sbin/update-rc.d -rwxr-xr-x 1 root root 4524 Nov 14 00:45 /usr/bin/update-alternatives -rwxr-xr-x 1 root root 5249 Nov 13 20:19 /etc/init.d/populate-volatile.sh -rwxr-xr-x 1 root root 6666 Nov 13 20:19 /etc/device_table -rwsr-xr-x 1 root root 9544 Nov 14 00:14 /usr/lib/eglibc/pt_chown -rwxr-xr-x 1 root root 9740 Nov 14 00:14 /lib/libutil-2.16.so -rwxr-xr-x 1 root root 13828 Nov 14 00:14 /lib/libdl-2.16.so -rw-r--r-- 1 root root 19398 Nov 14 00:45 /etc/services -rwxr-xr-x 1 root root 22020 Nov 14 00:14 /lib/libnss_dns-2.16.so -rwxr-xr-x 1 root root 26064 Nov 14 00:14 /lib/libcrypt-2.16.so -rwxr-xr-x 1 root root 30624 Nov 14 00:14 /lib/librt-2.16.so -rwxr-xr-x 1 root root 34588 Nov 14 00:14 /lib/libnss_compat-2.16.so -rwxr-xr-x 1 root root 46980 Nov 14 00:14 /lib/libnss_files-2.16.so -rwxr-xr-x 1 root root 83716 Nov 14 00:14 /lib/libresolv-2.16.so -rwxr-xr-x 1 root root 87860 Nov 14 00:14 /lib/libnsl-2.16.so -rwxr-xr-x 1 root root 96128 Nov 14 00:14 /lib/libpthread-2.16.so -rwxr-xr-x 1 root root 127228 Nov 14 00:14 /lib/ld-2.16.so -rwxr-xr-x 1 root root 251328 Nov 14 00:14 /lib/libm-2.16.so -rwxr-xr-x 1 root root 524924 Nov 14 00:14 /sbin/ldconfig -rwsr-xr-x 1 root root 554820 Nov 14 00:22 /bin/busybox -rwxr-xr-x 1 root root 1056128 Nov 14 00:14 /lib/libc-2.16.so
busybox, ldconfig and libc (and other libc-related libs) make up about 95% of the system.
If busybox were statically linked, and ldconfig and libc were omitted, I believe it would reduce the size of the system substantially.
exiting the system
There is no 'shutdown' command, but you can use 'ctrl-a to execute a command to the qemu monitor, and 'ctrl-a b' to issue a sysrq to the Linux kernel. You can do a sysrq-B to do a reboot. Do: ctrl-a h to see available commands, and ctrl-a x to exit qemu.
Resources
- Presentation: Tuning Linux For Embedded Systems: When Less Is More by Darren Hart, ELC Europe 2011, October 2011, Prague, Czech Republic
