写一个简单的程序调用，使用strace ./a.out，发现是没有拷贝libnss_files库。pwd可以使用file db，访问/etc/passwd文件。
openat(AT_FDCWD, "/etc/nsswitch.conf", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/lib/libnss_files.so.2", O_RDONLY|O_LARGEFILE|O_CLOEXEC) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/tls/v7l/neon/vfp/libnss_files.so.2", O_RDONLY|O_LARGEFILE|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/tls/v7l/neon/vfp", 0xbee544e0) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/tls/v7l/neon/libnss_files.so.2", O_RDONLY|O_LARGEFILE|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/tls/v7l/neon", 0xbee544e0) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/tls/v7l/vfp/libnss_files.so.2", O_RDONLY|O_LARGEFILE|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/tls/v7l/vfp", 0xbee544e0) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/tls/v7l/libnss_files.so.2", O_RDONLY|O_LARGEFILE|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/tls/v7l", 0xbee544e0) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/tls/neon/vfp/libnss_files.so.2", O_RDONLY|O_LARGEFILE|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/tls/neon/vfp", 0xbee544e0) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/tls/neon/libnss_files.so.2", O_RDONLY|O_LARGEFILE|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/tls/neon", 0xbee544e0) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/tls/vfp/libnss_files.so.2", O_RDONLY|O_LARGEFILE|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/tls/vfp", 0xbee544e0) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/tls/libnss_files.so.2", O_RDONLY|O_LARGEFILE|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/tls", 0xbee544e0) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/v7l/neon/vfp/libnss_files.so.2", O_RDONLY|O_LARGEFILE|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/v7l/neon/vfp", 0xbee544e0) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/v7l/neon/libnss_files.so.2", O_RDONLY|O_LARGEFILE|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/v7l/neon", 0xbee544e0) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/v7l/vfp/libnss_files.so.2", O_RDONLY|O_LARGEFILE|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/v7l/vfp", 0xbee544e0) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/v7l/libnss_files.so.2", O_RDONLY|O_LARGEFILE|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/v7l", 0xbee544e0) = -1 ENOENT (No such file or directory)