常见的文件系统有yaffs2, jffs2，他们是适用于根文件系统镜像存在于NAND Flash上的情况。而传统的Linux EXT2/EXT3文件系统格式适用于传统的block设备，比如SD卡或者硬盘。
cramfs同时适用于以上两种情况。其不管采用哪种格式，内核都必须支持它，这是根文件系统正确挂载的前提条件。其内核支持它是指:在对内核进行编译的时候必须加入对相应文件系统的支持。
由于在内核没有加入对yaffs2的支持，因此在最后根据mkyaffs2image制作yaffs2类型的根文件系统，在加载之前，必须要对linux内核进行打yaffs2的补丁。将yaffs文件系统编译进内核。之后在启动linux内核时候才能识别yaffs2文件系统。
我在自己的mini2440开发板上面通过nfs来加载制作好的"根文件系统"，这里的"根文件系统"指的是：没有经过像mkyaffs2image工具转化的原始的类linux目录结构的文件。其文件包括Linux启动时所必须的目录和关键性的文件。nfs便于加载及验证我们制作的文件系统的正确性。其加载时文件系统不用读写flash。
*******************************第一步：下载busybox并编译********************************
下载busybox-1.19.2.tar.bz2
http://www.busybox.net/downloads/
解压并进入目录
# tar jxvf busybox-1.19.2.tar.bz2
# cd busybox-1.19.2修改Makefile
# gedit Makefile &
把 164 行修改为:
CROSS_COMPILE = arm-linux-
把 190 行修改为:
ARCH = arm
配置
# make menuconfig 或者make xconfig(为图形化界面)
在Busybox Settings->Build Options之下选择Build BusyBox as a static binary (no shared libs) (STATIC)以静态的方式来编译busybox。
其他的比如安装目录及常用命令我没有设置，采用的是默认值。如果有需要再添加。
编译
# make
安装
# make install
在busybox-1.19.2目录下可以找到_install子目录，其中就是编译好的命令。
[busybox-1.19.2]$ll
total 12
drwxr-xr-x 2 root root 4096 Feb 9 14:43 bin
lrwxrwxrwx 1 root root 11 Feb 9 14:43 linuxrc -> bin/busybox
drwxr-xr-x 2 root root 4096 Feb 9 14:43 sbin
drwxr-xr-x 4 root root 4096 Feb 9 14:43 usr
并将以上文件copy到/mini2440/rootfs目录下面
*******************第二步：建立所需的目录及文件*************************
1： 建立目录
使用以下脚本
[root@centos /mini2440]$cat mkDir.sh //具有执行权限
#!/bin/sh
echo "------Create rootfs directons start...--------"
mkdir /mini2440/rootfs
cd /mini2440/rootfs
echo "--------Create root,dev....----------"
mkdir root dev etc boot tmp var sys proc lib mnt home usr
mkdir etc/init.d etc/rc.d etc/sysconfig
mkdir usr/sbin usr/bin usr/lib usr/modules
echo "make node in dev/console dev/null"
mknod -m 600 dev/console c 5 1
mknod -m 600 dev/null c 1 3
mkdir mnt/etc mnt/jffs2 mnt/yaffs mnt/data mnt/temp
mkdir var/lib var/lock var/run var/tmp
chmod 777 tmp
chmod 777 var/tmp
echo "-------make direction done---------"
上面shell中建立的目录有的没有使用。执行问脚本目录结构如下：
[root@centos /mini2440/rootfs]$ls
boot dev etc home lib mnt proc root sys tmp usr var
[root@centos /mini2440/rootfs]$tree
.
|-- boot
|-- dev
| |-- console
| `-- null
|-- etc
| |-- init.d
| |-- rc.d
| `-- sysconfig
|-- home
|-- lib
|-- mnt
| |-- data
| |-- etc
| |-- jffs2
| |-- temp
| `-- yaffs
|-- proc
|-- root
|-- sys
|-- tmp
|-- usr
| |-- bin
| |-- lib
| |-- modules
| `-- sbin
`-- var
|-- lib
|-- lock
|-- run
`-- tmp
28 directories, 2 files:
2：修改与添加系统初始化脚本 都在 /mini2440/rootfs目录下面进行
（1）etc/inittab 系统init进程配置文件，并更改权限 chmod +x inittab
::sysinit:/etc/init.d/rcS
::askfirst:-/bin/sh #没有这就不行，就不能打开console控制台。
::restart:/sbin/init
::ctrlaltdel:/sbin/reboot
::shutdown:/bin/umount -a -r
::shutdown:/sbin/swapoff -a
（2）etc/init.d/rcS系统启动加载项文件，并更改权限chmod +x etc/init.d/rcS
#!/bin/sh
PATH=/sbin:/bin:/usr/sbin:/usr/bin
runlevel=S
prevlevel=N
umask 022
export PATH runlevel prevlevel
mount -a
mkdir /dev/pts
mount -t devpts devpts /dev/pts #用于telnet登录时使用
echo /sbin/mdev > /proc/sys/kernel/hotplug
mdev -s
mkdir -p /var/lock
/bin/hostname -F /etc/sysconfig/HOSTNAME
（3）etc/fstab 系统挂载文件系统列表文件
#device mount-point type option dump fsck order
proc /proc proc defaults 0 0
sysfs /sys sysfs defaults 0 0
mdev /dev ramfs defaults 0 0
none /var ramfs defaults 0 0
none /tmp ramfs defaults 0 0
（4）etc/profile用户环境配置文件
# Ash profile
# vim: syntax= sh
# No core file by defaults
# ulimit - S - c 0> / dev/ null 2> & 1
USER="id -un"
LOGNAME=$USER
PS1="[\u@\h \w]#" #\w 目录将显示全路径
PATH=$PATH
HOSTNAME= '/bin/hostname'
alias cls="clear"
export USER LOGNAME PS1 PATH
（5）/etc/passwd shadow 用户文件以及密码
把主机的passwd shadow 文件拷贝到/etc下
# cp /etc/passwd /mini2440/rootfs/etc
# cp /etc/group /mini2440/rootfs/etc
# cp /etc/shadow /mini2440/rootfs/etc
（6）etc/sysconfig/HOSTNAME的内容为你自己的名字即可,内容为"mini2440"
gedit /etc/sysconfig/HOSTNAME 然后键入 mini2440
***********************第三步：以nfs方式加载测试********************************
测试之前必须确保nfs服务已经开启，uboot中的bootargs参数已经设置成功。
bootcmd=nfs 0x30008000 192.168.1.149:/opt/FriendlyARM/uImage;bootm
bootargs=noinitrd root=/dev/nfs proto=tcp,nolock,nfsvers=3, rw nfsroot=192.168.1.149:/mini2440/rootfs ip=192.168.1.144:192.168.1.149::255.255.255.0 console=ttySAC0,115200 init=/linuxrc mem=64M
在reboot的时候
[@mini2440 /etc]#reboot
[@mini2440 /etc]#umount: mdev busy - remounted read-only
是由于在reboot的时候执行了 /etc/inittab中的::shutdown:/bin/umount -a -r 需要重新挂载设备所致，可以去掉此行。
有待改进：使用mkyaffs2image制作成为最终的根文件系统，烧写到flash中，启动的时候从flash中读取内容。后面会做这一实验。
最终rootfs中的目录结构如下：
[root@centos /mini2440/rootfs]$tree
.
|-- bin
| |-- addgroup -> busybox
| |-- adduser -> busybox
| |-- ash -> busybox
| |-- base64 -> busybox
| |-- busybox
| |-- cat -> busybox
| |-- catv -> busybox
| |-- chattr -> busybox
| |-- chgrp -> busybox
| |-- chmod -> busybox
| |-- chown -> busybox
| |-- cp -> busybox
| |-- cpio -> busybox
| |-- cttyhack -> busybox
| |-- date -> busybox
| |-- dd -> busybox
| |-- delgroup -> busybox
| |-- deluser -> busybox
| |-- df -> busybox
| |-- dmesg -> busybox
| |-- dnsdomainname -> busybox
| |-- dumpkmap -> busybox
| |-- echo -> busybox
| |-- ed -> busybox
| |-- egrep -> busybox
| |-- false -> busybox
| |-- fdflush -> busybox
| |-- fgrep -> busybox
| |-- fsync -> busybox
| |-- getopt -> busybox
| |-- grep -> busybox
| |-- gunzip -> busybox
| |-- gzip -> busybox
| |-- hostname -> busybox
| |-- hush -> busybox
| |-- ionice -> busybox
| |-- iostat -> busybox
| |-- ip -> busybox
| |-- ipaddr -> busybox
| |-- ipcalc -> busybox
| |-- iplink -> busybox
| |-- iproute -> busybox
| |-- iprule -> busybox
| |-- iptunnel -> busybox
| |-- kill -> busybox
| |-- linux32 -> busybox
| |-- linux64 -> busybox
| |-- ln -> busybox
| |-- login -> busybox
| |-- ls -> busybox
| |-- lsattr -> busybox
| |-- lzop -> busybox
| |-- makemime -> busybox
| |-- mkdir -> busybox
| |-- mknod -> busybox
| |-- mktemp -> busybox
| |-- more -> busybox
| |-- mount -> busybox
| |-- mountpoint -> busybox
| |-- mpstat -> busybox
| |-- mt -> busybox
| |-- mv -> busybox
| |-- netstat -> busybox
| |-- nice -> busybox
| |-- pidof -> busybox
| |-- ping -> busybox
| |-- ping6 -> busybox
| |-- pipe_progress -> busybox
| |-- powertop -> busybox
| |-- printenv -> busybox
| |-- ps -> busybox
| |-- pwd -> busybox
| |-- reformime -> busybox
| |-- rev -> busybox
| |-- rm -> busybox
| |-- rmdir -> busybox
| |-- rpm -> busybox
| |-- run-parts -> busybox
| |-- scriptreplay -> busybox
| |-- sed -> busybox
| |-- setarch -> busybox
| |-- setserial -> busybox
| |-- sh -> busybox
| |-- sleep -> busybox
| |-- stat -> busybox
| |-- stty -> busybox
| |-- su -> busybox
| |-- sync -> busybox
| |-- tar -> busybox
| |-- touch -> busybox
| |-- true -> busybox
| |-- umount -> busybox
| |-- uname -> busybox
| |-- usleep -> busybox
| |-- vi -> busybox
| |-- watch -> busybox
| `-- zcat -> busybox
|-- boot
|-- dev
| |-- console
| |-- null
| `-- pts
|-- etc
| |-- fstab
| |-- fstab~
| |-- init.d
| | |-- rcS
| | `-- rcS~
| |-- inittab
| |-- inittab~
| |-- profile
| |-- rc.d
| `-- sysconfig
| |-- HOSTNAME
| `-- HOSTNAME~
|-- home
|-- lib
|-- linuxrc -> bin/busybox
|-- mnt
| |-- data
| |-- etc
| |-- jffs2
| |-- temp
| `-- yaffs
|-- proc
|-- root
|-- sbin
| |-- acpid -> ../bin/busybox
| |-- adjtimex -> ../bin/busybox
| |-- arp -> ../bin/busybox
| |-- blkid -> ../bin/busybox
| |-- blockdev -> ../bin/busybox
| |-- bootchartd -> ../bin/busybox
| |-- depmod -> ../bin/busybox
| |-- devmem -> ../bin/busybox
| |-- fbsplash -> ../bin/busybox
| |-- fdisk -> ../bin/busybox
| |-- findfs -> ../bin/busybox
| |-- freeramdisk -> ../bin/busybox
| |-- fsck -> ../bin/busybox
| |-- fsck.minix -> ../bin/busybox
| |-- getty -> ../bin/busybox
| |-- halt -> ../bin/busybox
| |-- hdparm -> ../bin/busybox
| |-- hwclock -> ../bin/busybox
| |-- ifconfig -> ../bin/busybox
| |-- ifdown -> ../bin/busybox
| |-- ifenslave -> ../bin/busybox
| |-- ifup -> ../bin/busybox
| |-- init -> ../bin/busybox
| |-- insmod -> ../bin/busybox
| |-- klogd -> ../bin/busybox
| |-- loadkmap -> ../bin/busybox
| |-- logread -> ../bin/busybox
| |-- losetup -> ../bin/busybox
| |-- lsmod -> ../bin/busybox
| |-- makedevs -> ../bin/busybox
| |-- man -> ../bin/busybox
| |-- mdev -> ../bin/busybox
| |-- mkdosfs -> ../bin/busybox
| |-- mke2fs -> ../bin/busybox
| |-- mkfs.ext2 -> ../bin/busybox
| |-- mkfs.minix -> ../bin/busybox
| |-- mkfs.vfat -> ../bin/busybox
| |-- mkswap -> ../bin/busybox
| |-- modinfo -> ../bin/busybox
| |-- modprobe -> ../bin/busybox
| |-- nameif -> ../bin/busybox
| |-- pivot_root -> ../bin/busybox
| |-- poweroff -> ../bin/busybox
| |-- raidautorun -> ../bin/busybox
| |-- reboot -> ../bin/busybox
| |-- rmmod -> ../bin/busybox
| |-- route -> ../bin/busybox
| |-- runlevel -> ../bin/busybox
| |-- setconsole -> ../bin/busybox
| |-- slattach -> ../bin/busybox
| |-- start-stop-daemon -> ../bin/busybox
| |-- sulogin -> ../bin/busybox
| |-- swapoff -> ../bin/busybox
| |-- swapon -> ../bin/busybox
| |-- switch_root -> ../bin/busybox
| |-- sysctl -> ../bin/busybox
| |-- syslogd -> ../bin/busybox
| |-- tunctl -> ../bin/busybox
| |-- udhcpc -> ../bin/busybox
| |-- vconfig -> ../bin/busybox
| |-- watchdog -> ../bin/busybox
| `-- zcip -> ../bin/busybox
|-- sys
|-- tmp
|-- usr
| |-- bin
| | |-- [ -> ../../bin/busybox
| | |-- [[ -> ../../bin/busybox
| | |-- add-shell -> ../../bin/busybox
| | |-- arping -> ../../bin/busybox
| | |-- awk -> ../../bin/busybox
| | |-- basename -> ../../bin/busybox
| | |-- beep -> ../../bin/busybox
| | |-- bunzip2 -> ../../bin/busybox
| | |-- bzcat -> ../../bin/busybox
| | |-- bzip2 -> ../../bin/busybox
| | |-- cal -> ../../bin/busybox
| | |-- chat -> ../../bin/busybox
| | |-- chpst -> ../../bin/busybox
| | |-- chrt -> ../../bin/busybox
| | |-- chvt -> ../../bin/busybox
| | |-- cksum -> ../../bin/busybox
| | |-- clear -> ../../bin/busybox
| | |-- cmp -> ../../bin/busybox
| | |-- comm -> ../../bin/busybox
| | |-- crontab -> ../../bin/busybox
| | |-- cryptpw -> ../../bin/busybox
| | |-- cut -> ../../bin/busybox
| | |-- dc -> ../../bin/busybox
| | |-- deallocvt -> ../../bin/busybox
| | |-- diff -> ../../bin/busybox
| | |-- dirname -> ../../bin/busybox
| | |-- dos2unix -> ../../bin/busybox
| | |-- du -> ../../bin/busybox
| | |-- dumpleases -> ../../bin/busybox
| | |-- eject -> ../../bin/busybox
| | |-- env -> ../../bin/busybox
| | |-- envdir -> ../../bin/busybox
| | |-- envuidgid -> ../../bin/busybox
| | |-- ether-wake -> ../../bin/busybox
| | |-- expand -> ../../bin/busybox
| | |-- expr -> ../../bin/busybox
| | |-- fdformat -> ../../bin/busybox
| | |-- fgconsole -> ../../bin/busybox
| | |-- find -> ../../bin/busybox
| | |-- flock -> ../../bin/busybox
| | |-- fold -> ../../bin/busybox
| | |-- free -> ../../bin/busybox
| | |-- ftpget -> ../../bin/busybox
| | |-- ftpput -> ../../bin/busybox
| | |-- fuser -> ../../bin/busybox
| | |-- groups -> ../../bin/busybox
| | |-- hd -> ../../bin/busybox
| | |-- head -> ../../bin/busybox
| | |-- hexdump -> ../../bin/busybox
| | |-- hostid -> ../../bin/busybox
| | |-- id -> ../../bin/busybox
| | |-- ifplugd -> ../../bin/busybox
| | |-- install -> ../../bin/busybox
| | |-- ipcrm -> ../../bin/busybox
| | |-- ipcs -> ../../bin/busybox
| | |-- kbd_mode -> ../../bin/busybox
| | |-- killall -> ../../bin/busybox
| | |-- killall5 -> ../../bin/busybox
| | |-- last -> ../../bin/busybox
| | |-- less -> ../../bin/busybox
| | |-- logger -> ../../bin/busybox
| | |-- logname -> ../../bin/busybox
| | |-- lpq -> ../../bin/busybox
| | |-- lpr -> ../../bin/busybox
| | |-- lspci -> ../../bin/busybox
| | |-- lsusb -> ../../bin/busybox
| | |-- lzcat -> ../../bin/busybox
| | |-- lzma -> ../../bin/busybox
| | |-- lzopcat -> ../../bin/busybox
| | |-- md5sum -> ../../bin/busybox
| | |-- mesg -> ../../bin/busybox
| | |-- microcom -> ../../bin/busybox
| | |-- mkfifo -> ../../bin/busybox
| | |-- mkpasswd -> ../../bin/busybox
| | |-- nc -> ../../bin/busybox
| | |-- nmeter -> ../../bin/busybox
| | |-- nohup -> ../../bin/busybox
| | |-- nslookup -> ../../bin/busybox
| | |-- od -> ../../bin/busybox
| | |-- openvt -> ../../bin/busybox
| | |-- passwd -> ../../bin/busybox
| | |-- patch -> ../../bin/busybox
| | |-- pgrep -> ../../bin/busybox
| | |-- pkill -> ../../bin/busybox
| | |-- pmap -> ../../bin/busybox
| | |-- printf -> ../../bin/busybox
| | |-- pscan -> ../../bin/busybox
| | |-- pstree -> ../../bin/busybox
| | |-- pwdx -> ../../bin/busybox
| | |-- readahead -> ../../bin/busybox
| | |-- readlink -> ../../bin/busybox
| | |-- realpath -> ../../bin/busybox
| | |-- remove-shell -> ../../bin/busybox
| | |-- renice -> ../../bin/busybox
| | |-- reset -> ../../bin/busybox
| | |-- resize -> ../../bin/busybox
| | |-- rpm2cpio -> ../../bin/busybox
| | |-- rtcwake -> ../../bin/busybox
| | |-- runsv -> ../../bin/busybox
| | |-- runsvdir -> ../../bin/busybox
| | |-- rx -> ../../bin/busybox
| | |-- script -> ../../bin/busybox
| | |-- seq -> ../../bin/busybox
| | |-- setkeycodes -> ../../bin/busybox
| | |-- setsid -> ../../bin/busybox
| | |-- setuidgid -> ../../bin/busybox
| | |-- sha1sum -> ../../bin/busybox
| | |-- sha256sum -> ../../bin/busybox
| | |-- sha512sum -> ../../bin/busybox
| | |-- showkey -> ../../bin/busybox
| | |-- smemcap -> ../../bin/busybox
| | |-- softlimit -> ../../bin/busybox
| | |-- sort -> ../../bin/busybox
| | |-- split -> ../../bin/busybox
| | |-- strings -> ../../bin/busybox
| | |-- sum -> ../../bin/busybox
| | |-- sv -> ../../bin/busybox
| | |-- tac -> ../../bin/busybox
| | |-- tail -> ../../bin/busybox
| | |-- tcpsvd -> ../../bin/busybox
| | |-- tee -> ../../bin/busybox
| | |-- telnet -> ../../bin/busybox
| | |-- test -> ../../bin/busybox
| | |-- tftp -> ../../bin/busybox
| | |-- tftpd -> ../../bin/busybox
| | |-- time -> ../../bin/busybox
| | |-- timeout -> ../../bin/busybox
| | |-- top -> ../../bin/busybox
| | |-- tr -> ../../bin/busybox
| | |-- traceroute -> ../../bin/busybox
| | |-- traceroute6 -> ../../bin/busybox
| | |-- tty -> ../../bin/busybox
| | |-- ttysize -> ../../bin/busybox
| | |-- udpsvd -> ../../bin/busybox
| | |-- unexpand -> ../../bin/busybox
| | |-- uniq -> ../../bin/busybox
| | |-- unix2dos -> ../../bin/busybox
| | |-- unlzma -> ../../bin/busybox
| | |-- unlzop -> ../../bin/busybox
| | |-- unxz -> ../../bin/busybox
| | |-- unzip -> ../../bin/busybox
| | |-- uptime -> ../../bin/busybox
| | |-- users -> ../../bin/busybox
| | |-- uudecode -> ../../bin/busybox
| | |-- uuencode -> ../../bin/busybox
| | |-- vlock -> ../../bin/busybox
| | |-- volname -> ../../bin/busybox
| | |-- wall -> ../../bin/busybox
| | |-- wc -> ../../bin/busybox
| | |-- wget -> ../../bin/busybox
| | |-- which -> ../../bin/busybox
| | |-- who -> ../../bin/busybox
| | |-- whoami -> ../../bin/busybox
| | |-- whois -> ../../bin/busybox
| | |-- xargs -> ../../bin/busybox
| | |-- xz -> ../../bin/busybox
| | |-- xzcat -> ../../bin/busybox
| | `-- yes -> ../../bin/busybox
| |-- lib
| |-- modules
| `-- sbin
| |-- brctl -> ../../bin/busybox
| |-- chpasswd -> ../../bin/busybox
| |-- chroot -> ../../bin/busybox
| |-- crond -> ../../bin/busybox
| |-- dhcprelay -> ../../bin/busybox
| |-- dnsd -> ../../bin/busybox
| |-- fakeidentd -> ../../bin/busybox
| |-- fbset -> ../../bin/busybox
| |-- ftpd -> ../../bin/busybox
| |-- httpd -> ../../bin/busybox
| |-- inetd -> ../../bin/busybox
| |-- loadfont -> ../../bin/busybox
| |-- lpd -> ../../bin/busybox
| |-- nbd-client -> ../../bin/busybox
| |-- ntpd -> ../../bin/busybox
| |-- popmaildir -> ../../bin/busybox
| |-- rdate -> ../../bin/busybox
| |-- rdev -> ../../bin/busybox
| |-- readprofile -> ../../bin/busybox
| |-- sendmail -> ../../bin/busybox
| |-- setfont -> ../../bin/busybox
| |-- setlogcons -> ../../bin/busybox
| |-- svlogd -> ../../bin/busybox
| |-- telnetd -> ../../bin/busybox
| |-- ubiattach -> ../../bin/busybox
| |-- ubidetach -> ../../bin/busybox
| |-- ubimkvol -> ../../bin/busybox
| |-- ubirmvol -> ../../bin/busybox
| |-- ubirsvol -> ../../bin/busybox
| |-- ubiupdatevol -> ../../bin/busybox
| `-- udhcpd -> ../../bin/busybox
`-- var
|-- lib
|-- lock
|-- run
| `-- utmp
`-- tmp
31 directories, 361 files