I'm using Debian 5.0 (Lenny) 64Bit on my server and my server has 4GB memory but unfortunately Debian shows 2 GB on /proc/meminfo and with "top" command. Do I need to use bigmem kernel with 64bit Debian?
No. Debian x64 supports up to 64 Tb. I use Debian 5.0 amd64(2.6.26-24lenny1)
Please, add output # lshw | grep "*-memory" -A 40