eAccelerator: Could not allocate xxx bytes, the maximum size the kernel allows is xxx bytes

eAccelerator is a open-source PHP accelerator & optimizer. It increases the performance of PHP scripts by caching them in their compiled state, so that the overhead of compiling is eliminated. It helps to speed the execution of scripts. eAccelerator usually speeds up your PHP code by a factor of 1–10 while lowering server load. Compiled PHP scripts are kept in shared memory by eAccelerator, which then runs code straight from there. It simply locks the screen for a brief period of time while looking through the cache for a compiled PHP script, allowing multiple engines to run the same script at once. Only files that are cached on disk will fit in shared memory.

When accessing any URL on your server, you might receive an error below.

eAccelerator: Could not allocate xxx bytes, the maximum size the kernel allows is xxx bytes. Lower the amount of memory request or increase the limit in /proc/sys/kernel/shmmax

The server-compiled eAccelerator is the cause of the aforementioned problem. PHP and the installed version of eAccelerator are not compatible. To correct the error, you can take two steps.

1. Increase memory in shmmax. Execute the commands below to increase memory.
   # echo “67108864” > /proc/sys/kernel/shmmax
   # sysctl -w kernel.shmmax=67108864
   # sysctl -p
   
2. Remove the unstable/incompatible version of eAccelerator and use PHP to create a fresh, stable version. Every server used for reseller and shared hosting has eAccelerator installed.