Build Root File System

Build Root File System on Mini2440

Startup Requirement

You need to have a compiled busybox and the kernel configure with Virtual File memory, NFS client support and the kernel level autoconfiguration function.

This build will create a new Root File System using the NFS service in the host computer to expose the contents to the target system, there is other method which is build a initrd image and booting with an initial RAM disk.

This is by no means a full system setup but a simple process to boot up a Linux system on Mini2440 as a start, alternatively there are tools that will automate the cross compiling process to generate the filesystem and software packages easily - such as Buildroot, OpenEmbedded and etc. which is another stages of learning process.

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Filesystem Hierarchy Standard

In order to build a Root File System i will follow the FHS rules to define the main directories and their layout content as below.

rootfs (/)
|--bin
|--dev
|--etc
|  |--init.d
|--lib
|--mnt
|--proc
|--sys
|--sbin
|--tmp
|--usr
|  |--bin
|  |--sbin
|--var

This RFS is mount as a root directory (/).

Note, there are two components to run a Linux system: the kernel and the RFS.

In this example, busybox is use as a base to construct the minimum set of files to support the system.

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Create Root Filesystem Strcuture

First, create a new root directory for our RFS, this directory is export as a NFS shared directory.

mkdir /rootfs

Copy the busybox system files into the root directory.

cd /rootfs
cp -a /usr/src/toolchain/busybox-1.16.0/_install/* .

Create the remaining FHS directories as require.

mkdir dev
mkdir -p etc/init.d
mkdir lib
mkdir mnt
mkdir proc
mkdir sys
mkdir -m 777 tmp
mkdir var

Copy the runtime libraries from the compiler system.

cd /rootfs/lib
cp -a /usr/local/arm/4.4.1/arm-none-linux-gnueabi/libc/armv4t/lib/* .

Make a serial console device as our system standard output.

cd /rootfs/dev
mknod -m 622 console c 5 1

When the kernel is running the last initialization action is to start the init program in charge of finalizing system startup by spawning various applications and running some key software components.

The operation of the init program is define in the inittab file, busybox init has the following default behaviour.

::sysinit:/etc/init.d/rcS
::askfirst:-/bin/sh
::ctrlaltdel:/sbin/reboot
::shutdown:/bin/umount -a -r
::shutdown:/sbin/swapoff -a
::restart:/sbin/init

Add a getty on the serial console to the above inittab, depending on the environment variable set in the bootargs (eg. console=ttySAC0) the same device to be set similarly.

::respawn:/sbin/getty -L 115200 /dev/ttySAC0 vt100

Create a rcS job file in the /rootfs/etc/init.d directory to initialize the target system.

#! /bin/sh

# Setup the bin file location and export to system PATH
PATH=/sbin:/bin:/usr/sbin:/usr/bin
umask 022
export PATH

# mount the filesystem directories
mount -a
mkdir /dev/pts
mount -t devpts devpts /dev/pts -o mode=0622

# create device nodes and directories
echo /sbin/mdev>/proc/sys/kernel/hotplug
mdev -s
mkdir /var/lock

# start logging utility services
klogd
syslogd

# set system clock from RTC
hwclock -s

# set host and config loopback interface
ifconfig lo 127.0.0.1

Create a mdev.conf file in the /rootfs/etc directory for the mdev process to do an initial update of the device files dynamically.

# system all-writable devices
full  0:0 0666
null  0:0 0666
ptmx  0:0 0666
random  0:0 0666
tty  0:0 0666
zero  0:0 0666

# console devices
tty[0-9]* 0:5 0660
vc/[0-9]* 0:5 0660

# serial port devices
s3c2410_serial0 0:5 0666 =ttySAC0
s3c2410_serial1 0:5 0666 =ttySAC1
s3c2410_serial2 0:5 0666 =ttySAC2
s3c2410_serial3 0:5 0666 =ttySAC3

# loop devices
loop[0-9]* 0:0 0660 =loop/

# i2c devices
i2c-0  0:0 0666 =i2c/0
i2c-1  0:0 0666 =i2c/1

# frame buffer devices
fb[0-9]  0:0 0666

# input devices
mice  0:0 0660 =input/
mouse.*  0:0 0660 =input/
event.*  0:0 0660 =input/
ts.*  0:0 0660 =input/

# rtc devices
rtc0  0:0 0644 >rtc
rtc[1-9] 0:0 0644

# misc devices
mmcblk0p1 0:0 0600 =sdcard */bin/hotplug
sda1  0:0 0600 =udisk * /bin/hotplug

Create a fstab filesystem table in the /rootfs/etc directory to mount the system directories.

# device mount-point type options dump fsck order
proc /proc proc defaults 0 0
sysfs /sys sysfs defaults 0 0
tmpfs /dev tmpfs defaults 0 0
tmpfs /tmp tmpfs defaults 0 0
var /var tmpfs defaults 0 0

Create a group file in /rootfs/etc directory.

grep root /etc/group>group

Create a password file in /rootfs/etc directory.

grep root /etc/passwd>passwd

Create a system wide 'profile' in /rootfs/etc directory.

USER="`id -un`"                                                 
LOGNAME=$USER                                                   
PS1='[\u@\h \W]\# '                                             
PATH=$PATH                                                      
HOSTNAME=`/bin/hostname`                                        
export USER LOGNAME PS1 PATH HOSTNAME

Create a /rootfs/etc/issue to add a welcome prompt to the console login.

Welcome to Mini2440
Kernel \r on an \m (\l)

Finally, create a resolv.conf file in /rootfs/etc directory to configure the DNS address to access the internet with your service provider network domain and ip address.

search internet.com.tw
nameserver 192.168.55.244                                         
nameserver 168.95.1.1

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Start up the NFS Server

Edit /etc/exports to configure the RFS as a shared directory.

/rootfs *(rw,sync,no_root_squash)

Start up the server.

service nfs restart

Verify the NFS server is running.

showmount -e 192.168.114.181

Export list for 192.168.114.181:
/rootfs *

Reboot the device to run the system.

Restarting system�

U-Boot 1.3.2-mini2440 (Feb 26 2010 - 17:34:45)

I2C:   ready
DRAM:  64 MB
Flash:  2 MB
NAND:  128 MiB
Found Environment offset in OOB..
USB:   S3C2410 USB Deviced
In:    serial
Out:   serial
Err:   serial
MAC: 08:00:2f:00:00:02
Hit any key to stop autoboot:  0

Loading from NAND 128MiB 3,3V 8-bit, offset 0x60000                     
Image Name:                                                          
Created:      2010-03-02  14:51:28 UTC                               
Image Type:   ARM Linux Kernel Image (uncompressed)                  
Data Size:    2053096 Bytes =  2 MB                                  
Load Address: 30008000                                               
Entry Point:  30008000                                               
## Booting kernel from Legacy Image at 32000000 ...                     
Image Name:                                                          
Created:      2010-03-02  14:51:28 UTC                               
Image Type:   ARM Linux Kernel Image (uncompressed)                  
Data Size:    2053096 Bytes =  2 MB                                  
Load Address: 30008000                                               
Entry Point:  30008000                                               
Verifying Checksum ... OK                                            
Loading Kernel Image ... OK                                          
OK                                                                      
                                                                
Starting kernel ...                                                     
                                                                
Uncompressing Linux.............................................................
Linux version 2.6.32.7 (root@gmax.localdomain) (gcc version 4.4.1 (Sourcery G++0
CPU: ARM920T [41129200] revision 0 (ARMv4T), cr=c0007177                
CPU: VIVT data cache, VIVT instruction cache                            
Machine: MINI2440                                                       
Memory policy: ECC disabled, Data cache writeback                       
CPU S3C2440A (id 0x32440001)                                            
S3C24XX Clocks, (c) 2004 Simtec Electronics                             
S3C244X: core 405.000 MHz, memory 101.250 MHz, peripheral 50.625 MHz    
CLOCK: Slow mode (1.500 MHz), fast, MPLL on, UPLL on                    
Built 1 zonelists in Zone order, mobility grouping on.  Total pages: 16256
Kernel command line: console=ttySAC0 noinitrd init=/sbin/init mini2440=0tb rootf
PID hash table entries: 256 (order: -2, 1024 bytes)                     
Dentry cache hash table entries: 8192 (order: 3, 32768 bytes)           
Inode-cache hash table entries: 4096 (order: 2, 16384 bytes)            
Memory: 64MB = 64MB total                                               
Memory: 60664KB available (3572K code, 388K data, 128K init, 0K highmem)
SLUB: Genslabs=11, HWalign=32, Order=0-3, MinObjects=0, CPUs=1, Nodes=1 
Hierarchical RCU implementation.                                        
NR_IRQS:85                                                              
irq: clearing subpending status 00000002                                
Console: colour dummy device 80x30                                      
console [ttySAC0] enabled                                               
Calibrating delay loop... 201.93 BogoMIPS (lpj=504832)                  
Mount-cache hash table entries: 512                                     
CPU: Testing write buffer coherency: ok                                 
NET: Registered protocol family 16                                      
MINI2440: Option string mini2440=0tb                                    
MINI2440: LCD [0:240x320] 1:800x480 2:1024x768 3:240x320 4:640x480      
S3C2440: Initialising architecture                                      
S3C2440: IRQ Support                                                    
S3C24XX DMA Driver, (c) 2003-2004,2006 Simtec Electronics               
DMA channel 0 at c4808000, irq 33                                       
DMA channel 1 at c4808040, irq 34                                       
DMA channel 2 at c4808080, irq 35                                       
DMA channel 3 at c48080c0, irq 36                                       
S3C244X: Clock Support, DVS off                                         
S3C24XX CPU Frequency driver, s3c244x cpu support                       
bio: create slab  at 0                                           
usbcore: registered new interface driver usbfs                          
usbcore: registered new interface driver hub                            
usbcore: registered new device driver usb                               
s3c-i2c s3c2440-i2c: slave address 0x10                                 
s3c-i2c s3c2440-i2c: bus frequency set to 98 KHz                        
s3c-i2c s3c2440-i2c: i2c-0: S3C I2C adapter                             
NET: Registered protocol family 2                                       
IP route cache hash table entries: 1024 (order: 0, 4096 bytes)          
TCP established hash table entries: 2048 (order: 2, 16384 bytes)        
TCP bind hash table entries: 2048 (order: 1, 8192 bytes)                
TCP: Hash tables configured (established 2048 bind 2048)                
TCP reno registered                                                     
NET: Registered protocol family 1                                       
RPC: Registered udp transport module.                                   
RPC: Registered tcp transport module.                                   
RPC: Registered tcp NFSv4.1 backchannel transport module.               
squashfs: version 4.0 (2009/01/31) Phillip Lougher                      
JFFS2 version 2.2. (NAND) �© 2001-2006 Red Hat, Inc.                    
msgmni has been set to 118                                              
alg: No test for stdrng (krng)                                          
io scheduler noop registered                                            
io scheduler anticipatory registered (default)                          
io scheduler deadline registered                                        
io scheduler cfq registered                                             
Console: switching to colour frame buffer device 60x53                  
fb0: s3c2410fb frame buffer device                                      
s3c2440-uart.0: ttySAC0 at MMIO 0x50000000 (irq = 70) is a S3C2440      
s3c2440-uart.1: ttySAC1 at MMIO 0x50004000 (irq = 73) is a S3C2440      
s3c2440-uart.2: ttySAC2 at MMIO 0x50008000 (irq = 76) is a S3C2440      
brd: module loaded                                                      
at24 0-0050: 1024 byte 24c08 EEPROM (writable)                          
S3C24XX NAND Driver, (c) 2004 Simtec Electronics                        
s3c24xx-nand s3c2440-nand: Tacls=1, 9ns Twrph0=3 29ns, Twrph1=2 19ns    
s3c24xx-nand s3c2440-nand: NAND soft ECC                                
NAND device: Manufacturer ID: 0xec, Chip ID: 0xf1 (Samsung NAND 128MiB 3,3V 8-b)
Creating 4 MTD partitions on "NAND 128MiB 3,3V 8-bit":                  
0x000000000000-0x000000040000 : "u-boot"                                
0x000000040000-0x000000060000 : "u-boot-env"                            
0x000000060000-0x000000560000 : "kernel"                                
0x000000560000-0x000008000000 : "root"                                  
dm9000 Ethernet Driver, V1.31                                           
eth0: dm9000e at c4860300,c4864304 IRQ 51 MAC: 08:00:2f:00:00:02 (chip) 
ohci_hcd: USB 1.1 'Open' Host Controller (OHCI) Driver                  
s3c2410-ohci s3c2410-ohci: S3C24XX OHCI                                 
s3c2410-ohci s3c2410-ohci: new USB bus registered, assigned bus number 1
s3c2410-ohci s3c2410-ohci: irq 42, io mem 0x49000000                    
usb usb1: configuration #1 chosen from 1 choice                         
hub 1-0:1.0: USB hub found                                              
hub 1-0:1.0: 2 ports detected                                           
usbcore: registered new interface driver libusual                       
mice: PS/2 mouse device common for all mice                             
input: gpio-keys as /devices/platform/gpio-keys/input/input0            
s3c2440-ts s3c2440-ts: Starting                                         
Created group ts filter len 12 depth 2 close 10 thresh 6              
Created Median ts filter len 20 depth 2 dec 24                        
Created Mean ts filter len 4 depth 2 thresh 65535                     
Created Linear ts filter depth 2                                      
s3c2440-ts s3c2440-ts: 4 filter(s) initialized                          
s3c2440-ts s3c2440-ts: successfully loaded                              
input: s3c2410 TouchScreen as /devices/virtual/input/input1             
S3C24XX RTC, (c) 2004,2006 Simtec Electronics                           
s3c2410-rtc s3c2410-rtc: rtc disabled, re-enabling                      
s3c2410-rtc s3c2410-rtc: rtc core: registered s3c as rtc0               
i2c /dev entries driver                                                 
S3C2410 Watchdog Timer, (c) 2004 Simtec Electronics                     
s3c2410-wdt s3c2410-wdt: watchdog inactive, reset disabled, irq enabled 
cpuidle: using governor ladder                                          
sdhci: Secure Digital Host Controller Interface driver                  
sdhci: Copyright(c) Pierre Ossman                                       
s3c-sdi s3c2440-sdi: powered down.                                      
s3c-sdi s3c2440-sdi: mmc0 - using pio, sw SDIO IRQ                      
Registered led device: led1                                             
Registered led device: led2                                             
Registered led device: led3                                             
Registered led device: led4                                             
Registered led device: backlight                                        
usbcore: registered new interface driver hiddev                         
usbcore: registered new interface driver usbhid                         
usbhid: v2.6:USB HID core driver                                        
Advanced Linux Sound Architecture Driver Version 1.0.21.                
No device for DAI UDA134X                                               
No device for DAI s3c24xx-i2s                                           
S3C24XX_UDA134X SoC Audio driver                                        
UDA134X SoC Audio Codec                                                 
asoc: UDA134X <-> s3c24xx-i2s mapping ok                                
ALSA device list:                                                       
#0: S3C24XX_UDA134X (UDA134X)                                         
TCP cubic registered                                                    
NET: Registered protocol family 17                                      
s3c2410-rtc s3c2410-rtc: setting system clock to 2008-12-27 10:22:30 UTC (12303)
eth0: link up, 100Mbps, full-duplex, lpa 0x45E1                         
IP-Config: Complete:                                                    
device=eth0, addr=192.168.114.190, mask=255.255.255.0, gw=192.168.114.1,
host=mini2440, domain=, nis-domain=(none),                         
bootserver=255.255.255.255, rootserver=192.168.114.181, rootpath=  
Looking up port of RPC 100003/2 on 192.168.114.181                      
Looking up port of RPC 100005/1 on 192.168.114.181                      
VFS: Mounted root (nfs filesystem) on device 0:13.                      
Freeing init memory: 128K                                               
                                                                
Please press Enter to activate this console.
[root@mini2440 /]#