原创 嵌入式linux根目录制作

（1）创建根文件系统的基本目录结构。
把这个过程做成shell脚本(红色部分) ，在要建立根目录的地方运行即可。?
#! /bin/sh
? echo "creatint rootfs dir......"
? mkdir rootfs
? cd rootfs

? echo "making dir : bin dev etc lib proc sbin sys usr"
? mkdir bin dev etc lib proc sbin sys usr #必备的8个目录
? mkdir usr/bin usr/lib usr/sbin lib/modules

? echo "making dir : mnt tmp var"
? mkdir mnt tmp var
? chmod 1777 tmp
? mkdir mnt/etc mnt/jffs2 mnt/yaffs mnt/data mnt/temp
? mkdir var/lib var/lock var/log var/run var/tmp?
? chmod 1777 var/tmp?

? echo "making dir : home root boot"
? mkdir home root boot

? echo "done"

在你想要建立根文件系统的地方，运行上面建立的脚本：?
$ ./mkroot
creatint rootfs dir......
making dir : bin dev etc lib proc sbin sys usr
making dir : mnt tmp var
making dir : home root boot
done
$ cd rootfs/dev/
$ su
口令：
# mknod -m 600 console c 5 1;mknod -m 666 null c 1 3;exit
Exit

（2）配置busybox
$ tar -xjvf busybox-1.9.1.tar.bz2
修改Makefile
kwrite Makefile

......(第174行附近)
#ARCH ?= $(SUBARCH)
#CROSS_COMPILE ?=
......(修改为)
ARCH = arm
CROSS_COMPILE = arm-linux-
使用menuconfig配置
$ make menuconfig

在原有的基础上修改如下：
Busybox Settings --->
? Build Options --->
?

build busybox as a static binary (no share libs) //（1）
? Installation Options --->
?

Don't use /usr //（2）
? (/home/linux/rootfs) BusyBox installation prefix?
? Busybox Library Tuning --->?
?

Support for /etc/networks?
?

Additional editing keys ?
?

vi-style line editing commands ?
? (15) History size ?
?

History saving ?
?

Tab completion?
?

Username completion ?

?

Fancy shell prompts

Linux System Utilities --->?
?

mdev //(3)
?

Support /etc/mdev.conf
?

Support command execution at device addition/removal
Linux Module Utilities ---> ?

? [N] Support version 2.2.x to 2.4.x Linux kernels?
Shells --->?
? --- Ash Shell Options 下的选项全选

编译安装
.1]$ make
......
?Library crypt is needed
?Library m is needed
Final link with: crypt m
$ make install

为mdev的运行准备环境
-----------------------------------------------
? mdev需要改写/dev和/sys两个目录。所以必须保证这两个目录是可写的(一般会用到sysfs,tmpfs。所以要重新编译内核)。然后在你的启动脚本文件中加入/sbin/mdev -s

linux-2.6.19 -- make menuconfig
File systems --->
? Pseudo filesystems --->?
?

sysfs file system support ?
?

Virtual memory file system support (former shm fs)?
?

Tmpfs POSIX Access Control Lists

常见问题
（1）因为busybox主要应用于对空间要求非常严格的嵌入式系统，所以它推荐使用uclibc而不鼓励使用glibc,如果你没有安装uclibc，而且在 build Options也选择了Build BusyBox as a static binary(no shared libs)，
Busybox Settings --->
? Build Options --->
?

build busybox as a static binary (no share libs)
那肯定无法编译通过的，当然如果你之前build Options选择的是动态编译的话就不会有这样的问题出现了。假设你是第一种情况，编译的时候将会遇到下面问题:
applets/applets.c:20:2: error: #warning Static linking against glibc produces buggy executables
applets/applets.c:21:2: error: #warning (glibc does not cope well with ld --gc-sections).
applets/applets.c:22:2: error: #warning See sources.redhat.com/bugzilla/show_bug.cgi?id=3400
applets/applets.c:23:2: error: #warning Note that glibc is unsuitable for static linking anyway.
applets/applets.c:24:2: error: #warning If you still want to do it, remove -Wl,--gc-sections
applets/applets.c:25:2: error: #warning from top-level Makefile and remove this warning.
make[1]: *** [applets/applets.o] Error 1

这段警告的意思是告诉你最好用uclibc编译，而不是用glibc因为glibc比较大，busybox在寸土寸金的嵌入式系统中运用比较多，所以会有这样的要求。
-----------------------------------------------
我们可以这样解决：把applets/applets.c开头的几行 warning注释掉

# vi applets/applets.c
/*
#if ENABLE_STATIC && defined(__GLIBC__) && !defined(__UCLIBC__)
#warning Static linking against glibc produces buggy executables
#warning (glibc does not cope well with ld --gc-sections).
#warning See sources.redhat.com/bugzilla/show_bug.cgi?id=3400
#warning Note that glibc is unsuitable for static linking anyway.
#warning If you still want to do it, remove -Wl,--gc-sections
#warning from top-level Makefile and remove this warning.
#error Aborting compilation.
#endif
*/
该情况在使用1.10.4版本时未出现

（2）miscutils/taskset.c:17: error: parse error before '*' token
-----------------------------------------------
最根本的解决办法是换一个libc库，可是现在还不知道哪个库最合适，唯有暂时将有问题的命令关掉
Miscellaneous Utilities --->
[ ] taskset

（3）runit/runsv.c: In function `gettimeofday_ns':
-----------------------------------------------

Runit Utilities --->
? [ ] runsv ?

（4）内核启动时遇到的问题:
-----------------------------------------------
“could not run '/bin/sh': No such file or directory”

解决方法:
要这样配置：
Shells ---> ?
? Choose your default shell (ash) ---> ?

如果是这样配置的话，虽然可以生成ash，但不能生成sh，将会在内核启动时出现上面出现的问题：
Shells ---> ?
? Choose your default shell (none) --->

ash?