You need to find out under which user your apache deamon runs.
You can do this by

root@ljstudio:/# cat /etc/httpd/conf/httpd.conf | grep "User"

And then:

root@ljstudio:/# su - apache -c 'ulimit -aHS' -s '/bin/bash'
core file size          (blocks, -c) 0
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 257402
max locked memory       (kbytes, -l) 64
max memory size         (kbytes, -m) unlimited
open files                      (-n) 1024
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 10240
cpu time               (seconds, -t) unlimited
max user processes              (-u) 1024
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

‘apache’ is usually used on CentOS, while on Ubuntu it’s expected to use www-data user instead.