http://busybox.net/downloads/BusyBox.html
LIBC NSS
GNU Libc (glibc) uses the Name Service Switch (NSS) to configure the behavior of the C library for the local environment, and to configure how it reads system data, such as passwords and group information. This is implemented using an /etc/nsswitch.conf configuration file, and using one or more of the /lib/libnss_* libraries. BusyBox tries to avoid using any libc calls that make use of NSS. Some applets however, such as login and su, will use libc functions that require NSS.
GNU Libc使用NSS来配置C库的行为，比如读取passwords和group。这是通过/etc/nsswitch.conf 和/lib/libnss_* 库来实现的。busybox避免使用libc的NSS，但是一些命令，如login和su还是使用libc的NSS
If you enable CONFIG_USE_BB_PWD_GRP, BusyBox will use internal functions to directly access the /etc/passwd, /etc/group, and /etc/shadow files without using NSS. This may allow you to run your system without the need for installing any of the NSS configuration files and libraries.
如果启用CONFIG_USE_BB_PWD_GRP，busybox会用内部的函数来访问/etc/passwd, /etc/group, and /etc/shadow 等文件。当程序中使用用户名和密码时要注意！
When used with glibc, the BusyBox 'networking' applets will similarly require that you install at least some of the glibc NSS stuff (in particular, /etc/nsswitch.conf, /lib/libnss_dns*, /lib/libnss_files*, and /lib/libresolv*).
Shameless Plug: As an alternative, one could use a C library such as uClibc. In addition to making your system significantly smaller, uClibc does not require the use of any NSS support files or libraries.
当使用glib时，busybox的网络相关命令（如ping）需要glibc和 NSS。如果ping 域名不同，可能就是少了这些库。
另外，可以参考我之前的文章：
http://www.cnblogs.com/cute/archive/2011/05/03/2035645.html
| libnss_dns | NSS routines for DNS. | Loaded automatically by the glibc NSS |
| libnss_files | NSS routines for file lookups. | Loaded automatically by the glibc NSS |
| libnss_hesiod | NSS routines for Hesiod name service. | Loaded automatically by the glibc NSS |
| libnss_nis | NSS routines for NIS. | Loaded automatically by the glibc NSS |
| libnss_nisplus | NSS routines for NIS plus. | Loaded automatically by the glibc NSS |
getpwnam失败，cp libnss-files过去就可以了。参考
Library Dependency 的議題要點 http://www.jollen.org/blog/2006/10/library_dependency_1.html
还可以通过strace来跟踪：http://www.xxlinux.com/linux/article/accidence/technique/20080221/13957.html
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http://www.jollen.org/blog/2006/10/name_service_switch.html
http://www.jollen.org/blog/2006/10/name_service_switch_1.html#more
root@james-desktop:/opt/qt-everywhere/marvell/SDK/initramfs/lib# arm-mv5sft-linux-gnueabi-readelf -s ./libnss_dns.so.2 | grep gethostbyname
37: 00001e2c 564 FUNC GLOBAL DEFAULT 12 _nss_dns_gethostbyname3_r@@GLIBC_PRIVATE
39: 00002100 56 FUNC GLOBAL DEFAULT 12 _nss_dns_gethostbyname2_r@@GLIBC_PRIVATE
40: 00002060 160 FUNC GLOBAL DEFAULT 12 _nss_dns_gethostbyname_r@@GLIBC_PRIVATE
root@james-desktop:/opt/qt-everywhere/marvell/SDK/initramfs/lib# arm-mv5sft-linux-gnueabi-readelf -s ./libnss_files.so.2 | grep gethostbyname
68: 00004ea4 1412 FUNC GLOBAL DEFAULT 12 _nss_files_gethostbyname_@@GLIBC_PRIVATE
97: 00004928 1404 FUNC GLOBAL DEFAULT 12 _nss_files_gethostbyname2@@GLIBC_PRIVATE
root@james-desktop:/opt/qt-everywhere/marvell/SDK/initramfs/lib# grep -rn "gethostbyname" *
二进制文件 libc-2.8.so 匹配
二进制文件 libc.so.6 匹配
二进制文件 libnss_dns-2.8.so 匹配
二进制文件 libnss_dns.so.2 匹配
二进制文件 libnss_files-2.8.so 匹配
二进制文件 libnss_files.so.2 匹配
二进制文件 libresolv-2.8.so 匹配
二进制文件 libresolv.so.2 匹配
root@james-desktop:/opt/qt-everywhere/marvell/SDK/initramfs/lib# arm-mv5sft-linux-gnueabi-readelf -s ./libc.so.6 | grep gethostbyname
692: 000dbfa8 808 FUNC GLOBAL DEFAULT 11 gethostbyname_r@@GLIBC_2.4
769: 000dbc6c 828 FUNC GLOBAL DEFAULT 11 gethostbyname2_r@@GLIBC_2.4
1291: 000db7c4 592 FUNC GLOBAL DEFAULT 11 gethostbyname@@GLIBC_2.4
1699: 000dba14 600 FUNC GLOBAL DEFAULT 11 gethostbyname2@@GLIBC_2.4