I wanted to make a ultra lite image that I can quickly drop Go programs onto. This image had a few requirements, be under 300MB, have less than 20MB ram usage idle, startup in under 5 seconds. I will post below everything I did to strip this down so that it can be replicated in the future. Currently with the steps below I have achieved 427MB/16MB, close to my goal for disk and memory usage is below the goal. As for bootup time, I am limited by network connection time 5+ seconds.
Install a fresh Raspbian Stretch Lite image into the SD card (source).
Configure headless SSH and Wi-Fi (if necessary) before starting the SD card (source).
$ mount /dev/sdX /media $ :> /media/ssh $ cat > /media/wpa_supplicant.conf <<"EOF" country=GB ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev update_config=1 network={ ssid="YOUR_SSID" psk="YOUR_PSK" } EOF $ umount /media $ sync
Replacing Openssh with dropbear in raspbian
Installation
To install on Raspbian, simply run the following two commands on your Pi:
apt update && apt install dropbear
Configuration
To enable dropbear, edit the config file with:
nano /etc/default/dropbear
and make sure NO_START matches below:
NO_START=0
and make sure the following is set:
DROPBEAR_PORT=22
22 is the default for SSH, but you can change it if you use another port for SSH(such as 443 or 80 to get around firewalls).
Disable SSH
You could just delete the OpenSSH server with
apt-get purge --yes --auto-remove openssh-server
Cleaning Disk Space
Get rid of some programs, I figured if I need any I will manually add them but for now kill everything for base image.
apt-get purge --yes --auto-remove aptitude aptitude-common apt-listchanges apt-utils blends-tasks xserver-common x11-xfs-utils x11-xserver-utils xinit libsmbclient blt gvfs gvfs-backends gvfs-daemons gvfs-fuse idle idle-python2.7 idle3 libaudio2 libice6 liblightdm-gobject-1-0 libpulse0 libqt4-svg libqtgui4 libsdl-image1.2 libsdl-mixer1.2 libsdl-ttf2.0-0 libsdl1.2debian libsm6 libsmpeg0 libwebkitgtk-1.0-0 libwebkitgtk-3.0-0 libxaw7 libxklavier16 libxmu6 libxss1 libxt6 libxtst6 lightdm lightdm-gtk-greeter lxde lxde-core midori obconf openbox python-pygame python-tk python3-tk scratch tk8.5 wpagui x11-common x11-utils x11-xkb-utils xinit xserver-common xserver-xorg xserver-xorg-core xserver-xorg-input-all xserver-xorg-input-evdev xserver-xorg-input-synaptics xserver-xorg-video-fbdev zenity xserver* x11-common x11-utils x11-xkb-utils x11-xserver-utils xarchiver xauth xkb-data console-setup xinit lightdm libx{composite,cb,cursor,damage,dmcp,ext,font,ft,i,inerama,kbfile,klavier,mu,pm,randr,render,res,t,xf86}* lxde* lx{input,menu-data,panel,polkit,randr,session,session-edit,shortcut,task,terminal} obconf openbox gtk* libgtk* alsa* python-pygame python-tk python3-tk scratch tsconf desktop-file-utils cifs-utils samba-common smbclient scratch debian-reference-en dillo idle3 python3-tk idle python-pygame python-tk lightdm gnome-themes-standard gnome-icon-theme raspberrypi-artwork gvfs-backends gvfs-fuse desktop-base lxpolkit zenity xdg-utils mupdf gtk2-engines alsa-utils lxde lxtask menu-xdg gksu midori xserver-xorg xinit xserver-xorg-video-fbdev libraspberrypi-dev libraspberrypi-doc dbus-x11 libx11-6 libx11-data libx11-xcb1 x11-common x11-utils lxde-icon-theme gconf-service gconf2-common udhcpd avahi-daemon gcc-arm-linux-gnueabihf geoip-database libgdbm* libperl* make patch perl perl-modules-* cups* rsync bluez bluez-firmware pi-bluetooth scratch debian-reference-en dillo idle3 python3-tk idle python-pygame python-tk lightdm gnome-themes-standard gnome-icon-theme raspberrypi-artwork gvfs-backends gvfs-fuse desktop-base lxpolkit zenity xdg-utils mupdf gtk2-engines alsa-utils lxde lxtask menu-xdg gksu midori xserver-xorg xinit xserver-xorg-video-fbdev libraspberrypi-dev libraspberrypi-doc dbus-x11 libx11-6 libx11-data libx11-xcb1 x11-common x11-utils lxde-icon-theme gconf-service gconf2-common firmware-atheros samba-common plymouth
Cleanup any leftover crud
apt-get autoremove --purge
Delete the default pi user
deluser pi && rm -rf /home/pi
kill config comments
find / -type f -name "*.conf" |xargs sed -i '\#^//#d'
Disable dpkg docs and locale files from installing via apt
cat > /etc/apt/apt.conf.d/80noadditional <<"EOF"
APT::Install-Recommends "0";
APT::Install-Suggests "0";
EOF
cat > /etc/dpkg/dpkg.cfg.d/nodoc <<"EOF"
path-exclude /usr/share/doc/* path-include /usr/share/doc/*/copyright path-exclude /usr/share/man/* path-exclude /usr/share/groff/* path-exclude /usr/share/info/* path-exclude /usr/share/lintian/* path-exclude /usr/share/linda/*
EOF
cat > /etc/dpkg/dpkg.cfg.d/nolocale <<"EOF"
path-exclude /usr/share/locale/*
EOF
Cleanup Logs, docs, useless files
find /usr/share/doc -depth -type f ! -name copyright | xargs rm
find /usr/share/doc -depth -type f ! -name copyright | xargs rm -f
find /usr/share/doc -empty | xargs rmdir
rm -rf /usr/share/man/* /usr/share/groff/* /usr/share/info/*
rm -rf /usr/share/lintian/* /usr/share/linda/* /var/cache/man/*
rm -rf /usr/share/locale/*
rm -f /var/log/{auth,boot,bootstrap,daemon,kern}.log
rm -f /var/log/{debug,dmesg,messages,syslog}
Disable MOTD for faster ssh connect
cat /dev/null > /etc/motd
Disable HDMI
Add the following to /etc/rc.local to disable hdmi on startup saving about 25mA of power usage.
/usr/bin/tvservice -o
Disable UART since we wont need it.
systemctl disable hciuart
More crud cleaning
apt-get clean
Other cleanup and optimizations
Add the following lines to your Pi’s /boot/config.txt file and reboot:
# http://rpf.io/configtxt
#https://www.raspberrypi.org/documentation/configuration/config-txt/overclocking.md
arm_freq=1100
#initial_turbo=30
#dtparam=i2c_arm=on
#dtparam=i2s=on
#dtparam=spi=on
# Disable stuff
dtparam=audio=off
dtoverlay=pi3-disable-bt
# Disable the ACT LED on the Pi Zero.
dtparam=act_led_trigger=none
dtparam=act_led_activelow=on
# Disable the splash screen
disable_splash=1
# Overclock the SD Card from 50 to 100MHz
# This can only be done with at least a UHS Class 1 card
dtoverlay=sdtweak,overclock_50=100
# Set the bootloader delay to 0 seconds. The default is 1s if not specified.
boot_delay=0
# Overclock the raspberry pi. This voids its warranty. Make sure you have a good power supply.
force_turbo=1
Quiet boot
Make the kernel output less verbose by adding the “quiet” flag to the kernel command line in file /boot/cmdline.txt. Make sure to change the PARTUUID if you copy and paste this line directly.
dwc_otg.lpm_enable=0 console=tty1 root=PARTUUID=8b037108-02 rootfstype=ext4 elevator=deadline fsck.repair=no quiet rootwait
Disabling some unneeded services
systemctl disable dphys-swapfile.service
systemctl disable apt-daily.service
systemctl disable apt-daily.timer
systemctl disable nfs-client.target
systemctl disable remote-fs.target
systemctl disable apt-daily-upgrade.timer
systemctl disable nfs-config.service
All I am left with now for memory usage. If anyone has suggestions on how to lower any let me know.
PID VIRT RES SHR S %CPU %MEM TIME+ COMMAND
1 9520 5876 4788 S 0.0 1.3 0:03.50 systemd
63 20500 4176 3792 S 0.0 0.9 0:00.83 systemd-journal
271 10064 4004 3492 S 0.0 0.9 0:00.02 wpa_supplicant
167 17100 3956 3524 S 0.0 0.9 0:00.22 systemd-timesyn
219 6816 3796 3440 S 0.0 0.9 0:00.14 systemd-logind
207 6396 3368 3000 S 0.0 0.8 0:00.28 dbus-daemon
89 14152 3200 2604 S 0.0 0.7 0:00.71 systemd-udevd
352 3476 2728 2316 S 0.0 0.6 0:00.13 bash
387 22628 2708 2284 S 0.0 0.6 0:00.04 rsyslogd
217 5200 2396 2196 S 0.0 0.5 0:00.03 cron
345 3868 1900 1780 S 0.0 0.4 0:00.02 agetty
351 2828 1816 1648 S 0.0 0.4 0:00.98 dropbear
346 4092 1804 1688 S 0.0 0.4 0:00.03 agetty
242 2360 1524 1420 S 0.0 0.3 0:00.00 dropbear
332 2780 1508 1192 S 0.0 0.3 0:00.00 dhcpcd
My disk usage unfortunately did not get as low as I wanted it.
Filesystem Size Used Avail Use% Mounted on
/dev/root 7.3G 428M 6.6G 7% /
devtmpfs 213M 0 213M 0% /dev
tmpfs 217M 0 217M 0% /dev/shm
tmpfs 217M 5.7M 212M 3% /run
tmpfs 5.0M 0 5.0M 0% /run/lock
tmpfs 217M 0 217M 0% /sys/fs/cgroup
/dev/mmcblk0p1 44M 22M 22M 51% /boot
Startup time
root@pi-b82xxxxxxx:~# systemd-analyze
Startup finished in 1.334s (kernel) + 16.235s (userspace) = 17.569s
root@pi-b827eb80a9a0:~# systemd-analyze blame
9.316s dhcpcd.service
4.058s dev-mmcblk0p2.device
3.033s networking.service
2.242s dropbear.service
1.795s systemd-logind.service
841ms systemd-journald.service
756ms systemd-udev-trigger.service
674ms systemd-remount-fs.service
601ms rsyslog.service
550ms systemd-fsck-root.service
537ms systemd-timesyncd.service
440ms systemd-fsck@dev-disk-by\x2dpartuuid-8b037108\x2d01.service
409ms systemd-udevd.service
391ms systemd-rfkill.service
313ms systemd-tmpfiles-setup-dev.service
309ms sys-kernel-debug.mount
306ms systemd-update-utmp.service
291ms dev-mqueue.mount
286ms systemd-tmpfiles-setup.service
285ms fake-hwclock.service
270ms kmod-static-nodes.service
262ms systemd-sysctl.service
249ms systemd-modules-load.service
244ms boot.mount
237ms systemd-journal-flush.service
158ms systemd-random-seed.service
126ms sys-kernel-config.mount
108ms systemd-user-sessions.service
93ms rc-local.service
90ms systemd-update-utmp-runlevel.service
78ms wifi-country.service
Download
I have uploaded the image for download. Up to date as of Jun 13th 2019 Image: ultra-minimal-pi.img.7z (113MB) Username: root Password: password
Additional imaging steps
So I don’t forget how to do it later for updates
On the pi run
cat /dev/zero > /tmp/zeros; sync; rm /tmp/zeros
For the rest I took the sd card and mounted it and imaged it using ubuntu disks utility
Use the following script from the download link to shrink the .img file
The finally compress it into a zip file
Sources: http://himeshp.blogspot.com/2018/08/fast-boot-with-raspberry-pi.html