How much memory is on my linux server? Run the free command

free -g 
 total       used       free     shared    buffers     cached
Mem:             2          1          0          0          0          1
-/+ buffers/cache:          0          1
Swap:            3          0          3

Which will tell you memory in Gigs. You can pass other flags, such as, -m or -k, which will give you the number in megs and kilobytes respectively.

The man page is as follows

man free
FREE(1)                                                                       Linux User's Manual                                                                      FREE(1)
NAME
free - Display amount of free and used memory in the system
SYNOPSIS
free [-b | -k | -m | -g] [-o] [-s delay ] [-t] [-V]
DESCRIPTION
free  displays the total amount of free and used physical and swap memory in the system, as well as the buffers used by the kernel.  The shared memory column should be
ignored; it is obsolete.
Options
The -b switch displays the amount of memory in bytes; the -k switch (set by default) displays it in kilobytes; the -m switch displays it in megabytes;  the  -g  switch
displays it in gigabytes.
   The -t switch displays a line containing the totals.

   The  -o  switch  disables the display of a "buffer adjusted" line.  If the -o option is not specified, free subtracts buffer memory from the used memory and adds it to
   the free memory reported.

   The -s switch activates continuous polling delay seconds apart. You may actually specify any floating point number for delay, usleep(3) is used for microsecond resolu-
   tion delay times.

   The -V displays version information.
FILES
/proc/meminfo
memory information
SEE ALSO
ps(1), slabtop(1), vmstat(8), top(1)

Just finishing up brewing up some fresh ground comments...