Hi Carlo,
Are you sure memcached is not running? or is it just monit that THINK it is not?
You can verify easily with:
# ps fax|grep memcached
which should show something like:
2025 ? Sl 2:14 /usr/bin/memcached -vv -m 128 -p 11211 -u memcache -l 127.0.0.1
Then you can also telnet to make sure it answers with:
# telnet 127.0.0.1 11211
if it is indeed running and the issue is only with monit not detecting it, then, does /var/run/memcached/memcached.pid exist and has the correct PID for memcached?
If not, try killing the current memcached process, removing /var/run/memcached/memcached.pid and use:
# /sbin/service memcached start
to start it again, then make sure /var/run/memcached/memcached.pid exists and has the correct PID.