redhat下编译的 uclinux的top命令 %CPU %MEM 怎么显示的是nan

9:05am up 24855 days, 3:14, 0 users, load average: nan, nan, nan
13 processes: 12 sleeping, 1 running, 0 zombie, 0 stopped
CPU states: 0.0% user, 0.7% system, 0.0% nice, 99.2% idle
Mem: 27100K av, 3016K used, 24084K free, 0K shrd, 800K buff
Swap: 0K av, 0K used, 0K free 800K cached

PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME COMMAND
48 root 13 15 352 352 260 R N nan nan 0:02 top
2 root 21 15 0 0 0 SWN nan nan 0:00 keventd
3 root 11 -4 0 0 0 SW< nan nan 0:00 ksoftirqd_CPU0
4 root 21 15 0 0 0 SWN nan nan 0:00 kswapd
1 root 21 15 276 272 216 S N nan nan 0:00 init
6 root 21 15 0 0 0 SWN nan nan 0:00 kupdated
36 root 21 15 232 232 180 S N nan nan 0:00 inetd
40 root 21 15 244 244 192 S N nan nan 0:00 thttpd
5 root 21 15 0 0 0 SWN nan nan 0:00 bdflush
42 root 21 15 220 220 180 S N nan nan 0:00 flatfsd
46 root 21 15 224 220 164 S N nan nan 0:00 telnetd
47 root 21 15 328 328 252 S N nan nan 0:00 sh
41 root 21 15 332 332 256 S N nan nan 0:00 sh