Linux rootfs (UBIFS)

The following switches to the root user to operate (the rootfs compiled in other user modes does not log in as root, which seems to be more troublesome, so let's keep it simple first)

Modify Makefile:

CROSS_COMPILE = /opt/arm-2010q1/bin/arm-none-linux-gnueabi-

ARCH = arm

After saving and exiting:

make menuconfig

1.18.1 has changed the make install directory to ./_install by default. And I don't plan to change it to a static library, so there is nothing to change. Let's take a look at it after saving and exiting:

make (build busybox)

make install (generate files to the _install directory)

Then modify the permissions of _install/bin/busybox:

chmod 4755 _install/bin/busybox

(Give busybox everyone readable and executable, the owner readable, writable and executable, 4 read, 2 write, 1 execute, 7=4+2+1, 5=4+1, the three are the owner, the owner group, and other groups. The first 4 means that when other users execute the file, the permissions are the same as the owner)

Enter the _install directory and create some directories required by Linux:

mkdir -p dev etc home lib mnt proc root sys tmp usr var/lib/misc var/lock var/log var/run var/tmp

And modify the permissions:

chmod 1777 tmp

chmod 1777 var/tmp

(The first one is prevented from being deleted by other users)

Create console and null devices under dev:

mknod -m 660 console c 5 1

mknod -m 660 null c 1 3

(These two devices are used for init startup)

Now let's take a look at what dynamic link libraries busybox needs. Return to the busybox directory and enter:

/opt/arm-2010q1/bin/arm-none-linux-gnueabi-readelf -a busybox  | grep Shared

It shows that libm.so.6 and libc.so.6 are required

Copy the library in the cross compiler to the _install/lib directory. Codesourcery's arm-2010q1, the default is armv5te, in the directory

In the lib under /opt /arm-2010q1/arm-none-linux-gnueabi/libc (corresponding to ARMv4T in armv4t, corresponding to armv7- a thumb2 in thumb2), since future applications may use these libraries except libm.so.6 and libc.so.6, copy all of them and execute under _install:

cp /opt/arm-2010q1/arm-none-linux-gnueabi/libc/lib/*.so*  lib -a

Then create some configuration files under _install/etc:

1 #

2 # /etc/fstab: static file system information.

3 #

4 #

5 #

6 # file system mount type options dump pass

7

8 #for mdev

9 proc /proc proc defaults 00

10 sysfs /sys sysfs defaults 00

11

12 #make sure /dev /tmp /var are tmpfs(tmpfs use ram as media) thus can be r/w

13 tmpfs /tmp tmpfs defaults 00

14 tmpfs /dev tmpfs defaults 00

15 tmpfs /var tmpfs defaults 00

16

17  #usbfs /proc/bus/usb usbfs defaults 0 0

The file system in fstab will be mounted by mount -a.

1 # see busybox/examples/inittab

2

3  # Boot-time system configuration/initialization script.

4 # This is run first except when booting in single-user mode.

5  ::sysinit:/etc/init.d/rcS

6

7  #Start an "askfirst" shell on the console (whatever that may be)

8 #use respawn instead askfirst to make sure console always active

9  ::respawn:-bin/sh

10

11  # Stuff to do when restarting the init process

12  ::restart:/sbin/init

13

14 # Stuff to do before rebooting

15 ::ctrlaltdel:/sbin/reboot

16 ::shutdown:/bin/umount -a -r

17 ::shutdown:/sbin/swapoff -a

18

19

inittab will be executed by init

1 #!/bin/sh

2

3 #add setting here for auto start program

4 PATH=/sbin:/bin:/usr/sbin:/usr/bin

5 runlevel=S

6 prevleval=N

7 umask 022

8 export PATH runlevel prevlevel

9

10 #See docs/mdev.txt

11 #mount all fs in fstab,proc and sysfs are must for mdev

12 mount -a

13

14 #create device nodes

15 echo /sbin/mdev >/proc/sys/kernel/hotplug

16

17 #seed all device nodes

18 mdev -s

19

20 #create pts directory for remote login such as SSH and telnet

21 mkdir -p /dev/pts

22 mount -t devpts devpts /dev/pts

23

24

25

26 if [ -f/etc/hostname ]; then

27 /bin/hostname -F/etc/hostname

28 fi

29

30 if [ -e /sys/class/net/eth0 ]; then

31 ifconfig eth0 192.168.1.15

32 fi

33

34 echo "etc init.d rcS done"

35

init.d/rcS will be automatically executed at boot time.

Change the permissions of rcS and inittab to 777:

chmod 777 init.d/rcS

chmod 777 inittab

There are also several files and directories:

The rc.d directory can store some self-starting scripts

mdev.conf (the content can be empty, you can also refer to busybox docs/mdev.txt)

profile

1 #id -un = whoami

2 export USER="id -un"

3 export LOGNAME=$USER

4 export PATH=$PATH

5

6 #a colorful prompt begin with "e[" end with "m"

7 export PS1='e[1;32mu@e[1;31mh#e[0m'

resolve.conf (marks the DNS server, just one sentence nameserver 202.96.134.133)

hostname (read by init.d/rcS, just a hostname, such as mx27)

passwd, group, shadow user/group/password can be replaced with those on the PC. Here are some instructions:

1 passwd consists of 7 fields, separated by 6 colons. Their meanings are:

2 1 Username

3 2 Whether there is an encryption password, x means yes, blank means no, MD5 and DES encryption are used.

4 3 User ID

5 4 Group ID

6 5 Comments field

7 6 Login Directory

8 7 Shell program used

9

10 Group consists of 4 fields, separated by 3 colons, and their meanings are:

11 1 Group Name

12 2 Is there an encrypted password? Same as passwd

13 3 Group ID

14 4 Array of pointers to user names

15

16 shadow consists of 9 fields, separated by 8 colons, and their meanings are:

17 1 Username

18 2 The encrypted password. If it is empty, it means that the user can log in without a password. If it is an asterisk, it means that the account is disabled. The above shows the encrypted password of 123456.

19 3 The number of days from January 1, 1970 to the last time the password was changed

20 4 The password cannot be changed by the user within a certain number of days

21 5 The number of days after which the password must be changed (0 means no change)

22 6 How many days after the password expires will the user account be banned?

23 7 How many days before the password expires should the user be warned?

24 8 Number of days the password has been banned since January 1, 1970

25 9 Reserved Domain

Now, except for the files in lib/modules/`uname -r`/kernel (`uname -r` is the Linux version of the development board, you can enter echo `uname -r` to view it), the rootfs is basically completed. Find the git address of mkfs in the FAQ of www.infradead.org (sweat, it's hard to find):

git clone git://git.infradead.org/mtd-utils.git

cd mtd-utils

git describe master (version number is v1.3.1-138-gf0cc488)

An error occurred when entering mkfs.ubifs. In the FAQ, I saw that three libraries were needed. I installed them:

sudo apt-get install zlib1g-dev

sudo apt-get install liblzo2-dev

sudo apt-get install uuid-dev

make successfully generates mkfs.ubifs

Then make _install into a ubifs file system:

./mkfs.ubifs -r /_install -m 512 -e 15360 -c 3897 -o ubifs.img

Among them, -m indicates the page size, -e indicates the logical erase block size, and -c indicates the maximum number of logical erase blocks. The specific information can be seen when executing ubiattach in barebox.

Power on and enter barebox:

erase /dev/nand0.root

ubiattach /dev/nand0.root

ubimkvol /dev/ubi0 root 0 (Note that the name here must match bootargs, the default is ubi0.root)

dhcp

tftp ubifs.img /dev/ubi0.root