Linux free output result description

The output result of linux free command is as follows: [root @ linux/tmp] # free total used free shared buffers cached Mem: 4149156 4130412 18744 0 13220 2720160-/+ buffers/cache: 1397032 2752124 Swap: 6289408 144 6289264 1st rows total memory: 4149156 used memory used: 4130412 free idle memory: 18744 shared memory is not used up currently, always 0 buffers Buffer Cache memory: 13220 cached Page Cache memory: 2720160 relationship: total = used + free 2nd rows: -/+ buffers/cache means: -Buffers/cache memory: 1397032 (equivalent to 1st rows of used-buffers-cached) + buffers/cache memory: 2752124 (equivalent to 1st rows of free + buffers + cached) it can be seen that-buffers/cache reflects the memory actually eaten by the program, while + buffers/cache reflects the total number of memories that can be used.