29号早上9点对一台Linux redhat 6 的VM(虚拟机)在调整CPU数(2->8)后发现，sar 查看当天CPU loading时，报错：
[root@vswhInd4DBt ~]# sar
Invalid system activity file: /var/log/sa/sa29
查看SYSSTAT官网
http://sebastien.godard.pagesperso-orange.fr/faq.html
主要说可能是因为sysstat版本变化照成saxx文件(/var/log/sa/sa29)格式的变化，不兼容导致不可读sarxx文件
Invalid system activity file: ...
You are trying to use a file which is not a system activity file, or whose format is no longer compatible with that of files created by current version of sar.
If you were trying to use the standard system activity files located in the /var/log/sa directory then the solution is easy: Just log in as root and remove by hand all the files located in the /var/log/sa directory:
# rm /var/log/sa/sa??
If you are using sysstat 11.1.1 and later, you can also use the sadf command to convert an old system activity binary datafile (version 9.1.6 and later) to current up-to-date format. Use the following syntax:
$ sadf -c old_datafile > new_datafile
Note: Starting with sysstat version 8.1.1 and later, it is possible to know which version of sar or sadc has been used to create a data file. Just enter the following command:
$ sadf -H /your/datafile | grep sysstat
File created using sar/sadc from sysstat version 8.1.7
回到我的环境，sysstat版本并没有变化。
怀疑因为CPU数的变化，导致saxx文件记录及运算的变化，使saxx文件写入失败sar不可读。
准备等30号再看是否正常，果然命令显示正常：
[root@vswhInd4DBt ~]# sar
Linux 2.6.32-504.el6.x86_64 (vswhInd4DBt) 07/30/2018 _x86_64_ (8 CPU)
00:01 AM CPU %user %nice %system %iowait %steal %idle
10:01 AM all 0.48 0.00 0.11 0.12 0.00 99.29
01 AM all 0.27 0.00 0.10 0.06 0.00 99.57
02 AM all 0.21 0.00 0.08 0.02 0.00 99.68
...
当然，在29号对CPU调整后rm -rf /var/log/sa/sa29 ，sar命令应该也能显示出调整后的信息
