It seems that "shm_put_var()" has a problem with the
calculation of free space for setting a variable the
second time. I guess it calculates the remaining free
space including the size taken by the old variable

<?php
$str=str_repeat("-",30); // 52 (max which fits in 100) is even worse
$shm=shm_attach(0xfffe,100);
shm_put_var($shm,1,$str);
//shm_put_var($shm,1,0); // using that will make next statement work without error
shm_put_var($shm,1,$str); // THIS will tell you there is not enoug memory left!
shm_detach($shm);
shm_remove(0xfffe);
?>

Sincerely,
 Hans Raaf