check memory in linux

1) free:
total used free shared buffers cached
Mem: 4060988 1231108 2829880 0 37504 532256
-/+ buffers/cache: 661348 3399640
Swap: 4626608 0 4626608

This means that the total memory is 4G and 2.8G is still available.

2) dmesg:
shows you the last status messages reported by your OS kernel, and since every boot procedure includes scanning the hardware and confirming the devices and resources recognized by the kernel, you can see some basic information by using dmesg.

dmesg |grep Memory
Memory: 4056564k/5242880k available (3370k kernel code, 1051444k absent, 134872k reserved, 1934k data, 644k init)

3) /proc/meminfo:
/proc/meminfo is a clear text presentation of the most vital memory stats of your system and we can use cat /proc/meminfo to see all the parameters