More detailed error message below:

     | ./var/cache/fontconfig/
     | ./var/cache/fontconfig/707971e003b4ae6c8121c3a920e507f5-le32d4.cache-3
     | ./var/cache/fontconfig/fe547fea3a41b43a38975d292a2b19c7-le32d4.cache-3
     | ./var/cache/fontconfig/c855463f699352c367813e37f3f70ea7-le32d4.cache-3
     | ./var/cache/fontconfig/94322f4d3cdf1bd54794b691285ca062-le32d4.cache-3
     | ./var/cache/fontconfig/CACHEDIR.TAG
     | ./var/cache/fontconfig/3830d5c3ddfd5cd38a049b759396e72e-le32d4.cache-3
     | ./var/cache/fontconfig/6333f38776742d18e214673cd2c24e34-le32d4.cache-3
     | ./var/cache/rpm/
     | ./var/cache/ldconfig/
     | ./var/cache/ldconfig/aux-cache
     | tar: .: file changed as we read it


If we are building a read-only rootfs, this error will appear now and then.
The root cause is that we spawn background process in populate-volatile.sh.

//Chen Qi