Problem scenario
You get an error about memcache and you are running PHP. Or you get an error "Unable to load dynamic library "memcached.so"? You run "php --version" and you see an error about memcache or memcached (e.g., a missing memcached.so file). What should you do?
Possible Solution #1
Get a memcached.so file from a working Linux server and place it in the directory that the error message showed in the php --version command. If the OS is the exact same as a working server, you could try the location mentioned in the error message. Alternatively you could run this to find it: sudo find / -name memcached.so
Possible Solution #2
You could run this (where "/path/to/pecl" is the result of this command "which pecl"):
sudo /path/to/pecl install memcached
Possible Solution #3
Check the permissions of the memcached.so file if it exists. The file may have incorrect permissions that keep it from being usable.
Possible Solution #4
Is the memcached.so file corrupt or too small? There may be a problem with it. You may need to recreate it. You may want to back it up before you recreate it just to be sure.
Possible Solution #5
If you are using brew, see this posting: https://stackoverflow.com/questions/7860404/how-to-enable-the-memcached-php-extension-after-installing-with-homebrew
For future reference:
To find the version of memcached installed, try these commands:
rpm -qi libmemcached
yum list installed | grep memcache
which memcached
memcached -h