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Arch Minimal

Arch Minimal¶

Because bloat is EVIL

And there are various valid use cases for smaller installations

Old/minimal hardware
Chroots
Containers
System on USB
Embedded systems
Routers
Firewalls
NAS devices
...

<rant>
Also - for such a streamlined OS what is with the install requirements...
base group needs 256MB RAM and 800MB disk ... really ...
</rant>

First line from the home page claims that it is "A simple, lightweight distribution"

I'll assume simple means for people who are already expert sysadmins...
It is my favorite "distribution" but that doesn't mean I'm such a fanboy that I can't point out flaws ;)

Requirements from the Beginners' guide

Arch Linux should run on any i686 compatible machine with a minimum of 256 MB RAM. A basic installation with all packages from the base group should take less than 800 MB of disk space.

Goals¶

~~Using QEMU boot to bash as init as baseline~~
1. ~~Use plan9fs to allow Underlying ZFS Goodness (tm)~~
~~Only what is required and used will be included~~
1. ~~Firewall style default deny~~
Account for the differences between the filesystem and the packages
1. Using the awesome find.differences ;)
Modular
1. Including a rule file should be enough to pull in everything related
2. particularly things like locales, man pages, info pages, ...
  1. Think an NFS rule file ... maybe ... eventually
Simple and modern system ... no Amish support
1. no i'm not using rarpd or NIS (even NIS+)
2. do i want to waste memory on nscd up to 32MB per file for a few lookups on /etc/services
Follow FSHS
1. without being stupid and possibly following some of the exception trends
Self hosting
1. Kernel and initrd are in the image
2. initrd can be made inside the image
3. Packages can be upgraded/installed (both minimally) from inside the VM
Full init with systemd
Use TOMOYO to validate what is used

Success¶

Managed to get a "working" if not slightly crippled boot to bash in 4.4M and 62 Files
(technically 3.6M in 18 files excluding pacman stuff in /var)

Down from 140M and 8K files from the bash baseline :)

TODO how does /tmp get created???¶

And as expected when you exit the shell ;)

bash-4.3# exit 34
[ 1365.738418] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00002200
[ 1365.738418]
[ 1365.740905] CPU: 0 PID: 1 Comm: bash Not tainted 4.4.5-1-ARCH #1
[ 1365.741705] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.9.1-20160216_104851-anatol 04/01/2014
[ 1365.741705]  0000000000000086 00000000dd214654 ffff880006d0fe10 ffffffff812cb391
[ 1365.741705]  ffffffff81717488 ffff880006d0fea8 ffff880006d0fe98 ffffffff81163368
[ 1365.741705]  0000000000000010 ffff880006d0fea8 ffff880006d0fe40 00000000dd214654
[ 1365.741705] Call Trace:
[ 1365.741705]  [<ffffffff812cb391>] dump_stack+0x63/0x82
[ 1365.741705]  [<ffffffff81163368>] panic+0xd3/0x215
[ 1365.741705]  [<ffffffff8115c3ee>] ? perf_event_exit_task+0xbe/0x350
[ 1365.741705]  [<ffffffff8107ab2a>] do_exit+0xb0a/0xb10
[ 1365.741705]  [<ffffffff81065426>] ? __do_page_fault+0x1a6/0x450
[ 1365.741705]  [<ffffffff8107abab>] do_group_exit+0x3b/0xb0
[ 1365.741705]  [<ffffffff8107ac34>] SyS_exit_group+0x14/0x20
[ 1365.741705]  [<ffffffff815970ee>] entry_SYSCALL_64_fastpath+0x12/0x6d
[ 1365.741705] Kernel Offset: disabled
[ 1365.741705] ---[ end Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000000
[ 1365.741705]

The "full" filesystem Show Hide

# ls -l --almost-all --human --recursive
.:
total 2.5K
drwxr-xr-x 2 root root 3 May 12 04:49 etc
lrwxrwxrwx 1 root root 7 Sep 30  2015 lib64 -> usr/lib
drwxrwxrwt 2 root root 2 May 12 04:42 tmp
drwxr-xr-x 4 root root 4 May 12 04:42 usr
drwxr-xr-x 3 root root 3 May 12 04:42 var

./etc:
total 8.5K
-rw-r--r-- 1 root root 365 May 12 04:49 ld.so.cache

./tmp:
total 0

./usr:
total 13K
drwxr-xr-x 2 root root  3 May 12 04:42 bin
drwxr-xr-x 2 root root 12 May 12 04:42 lib

./usr/bin:
total 1.1M
-rwxr-xr-x 1 root root 773K Nov 23 22:20 bash

./usr/lib:
total 3.5M
-rwxr-xr-x 1 root root 169K May  2 10:59 ld-2.23.so
lrwxrwxrwx 1 root root   10 May 12 04:42 ld-linux-x86-64.so.2 -> ld-2.23.so
-rwxr-xr-x 1 root root 1.9M May  2 10:59 libc-2.23.so
lrwxrwxrwx 1 root root   12 May 12 04:42 libc.so.6 -> libc-2.23.so
-rwxr-xr-x 1 root root  15K May  2 10:59 libdl-2.23.so
lrwxrwxrwx 1 root root   13 May 12 04:42 libdl.so.2 -> libdl-2.23.so
lrwxrwxrwx 1 root root   18 Dec  5 17:44 libncursesw.so.6 -> libncursesw.so.6.0
-rwxr-xr-x 1 root root 435K Dec  5 17:45 libncursesw.so.6.0
lrwxrwxrwx 1 root root   18 Sep 18  2015 libreadline.so.6 -> libreadline.so.6.3
-r-xr-xr-x 1 root root 338K Sep 18  2015 libreadline.so.6.3

./var:
total 512
drwxr-xr-x 3 root root 3 May 12 04:42 lib

./var/lib:
total 512
drwxr-xr-x 4 root root 4 May 12 04:42 pacman

./var/lib/pacman:
total 13K
drwxr-xr-x 10 root root 11 May 12 04:42 local
drwxr-xr-x  2 root root  3 May 12 04:42 sync

./var/lib/pacman/local:
total 4.5K
-rw-r--r-- 1 root root 2 May 12 04:42 ALPM_DB_VERSION
drwxr-xr-x 2 root root 6 May 12 05:00 bash-4.3.042-4
drwxr-xr-x 2 root root 6 May 12 05:01 filesystem-2015.09-1
drwxr-xr-x 2 root root 5 May 12 04:42 gcc-libs-6.1.1-1
drwxr-xr-x 2 root root 6 May 12 05:01 glibc-2.23-2
drwxr-xr-x 2 root root 5 May 12 04:42 linux-api-headers-4.5.2-1
drwxr-xr-x 2 root root 5 May 12 04:42 ncurses-6.0-4
drwxr-xr-x 2 root root 6 May 12 05:01 readline-6.3.008-3
drwxr-xr-x 2 root root 5 May 12 04:42 tzdata-2016d-1

./var/lib/pacman/local/bash-4.3.042-4:
total 42K
-rw-r--r-- 1 root root  435 May 12 04:42 desc
-rw-r--r-- 1 root root 4.2K May 12 04:42 files
-rw-r--r-- 1 root root  400 Nov 23 22:20 install
-rw-r--r-- 1 root root 5.4K Nov 23 22:20 mtree

./var/lib/pacman/local/filesystem-2015.09-1:
total 34K
-rw-r--r-- 1 root root  294 May 12 04:42 desc
-rw-r--r-- 1 root root 1.5K May 12 04:42 files
-rw-r--r-- 1 root root 2.0K Sep 30  2015 install
-rw-r--r-- 1 root root 2.6K Sep 30  2015 mtree

./var/lib/pacman/local/gcc-libs-6.1.1-1:
total 26K
-rw-r--r-- 1 root root  342 May 12 04:42 desc
-rw-r--r-- 1 root root 1.6K May 12 04:42 files
-rw-r--r-- 1 root root 2.9K May  2 07:52 mtree

./var/lib/pacman/local/glibc-2.23-2:
total 242K
-rw-r--r-- 1 root root  339 May 12 04:42 desc
-rw-r--r-- 1 root root  42K May 12 04:42 files
-rw-r--r-- 1 root root   49 May  2 10:59 install
-rw-r--r-- 1 root root 102K May  2 10:59 mtree

./var/lib/pacman/local/linux-api-headers-4.5.2-1:
total 146K
-rw-r--r-- 1 root root 312 May 12 04:42 desc
-rw-r--r-- 1 root root 24K May 12 04:42 files
-rw-r--r-- 1 root root 58K May  2 05:28 mtree

./var/lib/pacman/local/ncurses-6.0-4:
total 406K
-rw-r--r-- 1 root root  451 May 12 04:42 desc
-rw-r--r-- 1 root root 113K May 12 04:42 files
-rw-r--r-- 1 root root 162K Dec  5 17:45 mtree

./var/lib/pacman/local/readline-6.3.008-3:
total 34K
-rw-r--r-- 1 root root  352 May 12 04:42 desc
-rw-r--r-- 1 root root 1.3K May 12 04:42 files
-rw-r--r-- 1 root root  410 Sep 18  2015 install
-rw-r--r-- 1 root root 3.0K Sep 18  2015 mtree

./var/lib/pacman/local/tzdata-2016d-1:
total 242K
-rw-r--r-- 1 root root  305 May 12 04:42 desc
-rw-r--r-- 1 root root  69K May 12 04:42 files
-rw-r--r-- 1 root root 100K Apr 19 18:32 mtree

./var/lib/pacman/sync:
total 249K
-rw-r--r-- 1 root root 121K May 10 09:18 core.db

Package Notes ¶

Notes for installed packages

Baselines¶

For these baselines the cache is not kept in the VM
Nor is /etc/pacman.d/gnupg
(mainly because it isn't implemented yet and doesn't help with the statistics anyway)

Baseline for `pm.bootstrap`¶

basically just filesystem and its stupid dependency on iana-etc

# du --summarize --human-readable --apparent-size new_root/
9.1M    new_root/

# find new_root/ | wc --lines
115

Baseline for `pm -S bash`¶

Installs 7 packages
(enabling qemu.start to succeed)

# du --summarize --human-readable --apparent-size new_root/
139M    new_root/

# find new_root/ | wc --lines
8125

... seriously???

140M and 8K files to use bash as init???

Baseline for `pm -S base`¶

Installs 50 packages which blossom to 125 with dependencies
(supporting my rant above)
(also allows booting into systemd && shutting down :) )

Total Installed Size:  610.27 MiB

# du --summarize --human-readable --apparent-size new_root/
627M    new_root/

# find new_root/ | wc --lines
34819

Awesome...

Though in fairness it will "boot" to bash as init in 48M of ram under QEMU
32M caused a boot-loop though this may have to do with the size of the initrd...
When booted to bash with 48M it shows 19M free ...
When booted to systemd with 48M it shows 10M free ...
The least it can boot to systemd with is 42M showing 5M free ... of course 42 is THE answer :)
(free -h)

42 is also the minimum for booting to bash showing 14M free
BUT strangely not reliably ... sometimes it actually OOMed and continued booting :(
(got to love non-deterministic ~~testing~~ computing)

41M and it almost boots then locks hard :P

Also keep in mind this has nothing to do with running anything real and possibly the extra RAM requirements are necessary for making it through a full installation from CD/USB without swapping or OOMing

TODO link to the answer¶

The current initrd with plan9 magic¶

Consumes

# du --summarize --human --apparent-size .
13M    .

# find . | wc --lines
343

How to do stuff with just bash...¶

TODO check all the built-ins and functions¶

cd and tab for ls

because we like cats

cat ()
{
    echo "$(<$1)" 
}

free

cat /proc/meminfo

Future Goal Options¶

Check the bash man page for ^INVOCATION

dash instead of bash for speed?
(watch out for bashism breakage)

Maybe look at minimal window managers there was a 9k one

Some BG dude
#232

8k init

dracut like 5 second boot

run completely from ramfs?

Is lz4 statically inside the kernel for compression?
What about cramfs for no memory overhead decompression?

Seriously 600MB of ram to install the base system???

zram
Ubuntu Linux Considers Greater Usage Of zRAM - Phoronix Forums
compcache - Performance.wiki
systemd-swap/systemd-swap.conf at master · Nefelim4ag/systemd-swap · GitHub
https://www.kernel.org/doc/Documentation/vm/zswap.txt
https://www.kernel.org/doc/Documentation/blockdev/zram.txt

use ldd and other "tricks" to figure out what libraries are necessary and what really depends on what

is readline/history built into bash for arch?

Flavors - bare minimum

can use all cheats like diet libc and busybox

Real small (emphasis on real)

using stripped packages

udev for stacked device discovery?

Only systemd - no sysv legacy crap

vim - a real editor

pacman package management

cryptsetup / encrypted root

log rotation

no additional languages by default

?standard kernel?
?All modules?

?RAID/ZFS? Or more specifically is it a recovery medium

Maybe no lvm2

Probably include i686 - for older hardware

?Self hosting for installs?

Every file and dependency should be accounted for by TOYMO (SP?)

Should follow FSHS

TODO - ADD links for TOYMO and FSHS¶

Boot time a priority?

Tuning?

Somewhat Related Minimal References¶

Linux from scratch General Libraries and Utilities
Linux from scratch which which

Archboot - ArchWiki
GNU Project - ArchWiki
From Power Up To Bash Prompt
From Power Up To Bash Prompt.
Cisco Bug: CSCub38011 - Nexus 5k might boot to bash prompt
Fabric Interconnect booting to bash? | JeffSaidSo
From Power Up To Bash Prompt
From Power Up To Bash Prompt.
From Power Up To Bash Prompt: Building Software From Source
Index of /Linux/redhat/archive.redhat.com/redhat/linux/7.1/es/doc/HOWTOS/other-formats/html/From-PowerUp-To-Bash-Prompt-HOWTO-html
Init - ArchWiki
Minimal Linux with kernel and BusyBox: /etc/inittab is ignored, only /init is executed - Unix & Linux Stack Exchange
minit
GitHub - Yelp/dumb-init: A minimal init system for Linux containers
Tim Potter's Netwinder Things - Building a Minimal Linux System
What is the minimal init.d script for Ubuntu? - Server Fault
Joshua Go's Linux Guide - Creating a Minimal Linux Filesystem
linux - Simple replacement of init to just start console - Stack Overflow
A minimal init script [LWN.net]

Old naming ideas¶

"bear minimum" arch linux (too many misspelled hits)
"TBV - Trust But Verify" (not sure it is intuitive)

Geeky Stuff

Wiki