Free
free - Display amount of free and used memory in the system, as well as the buffer used by the kernel, and the used physical and swap memory.
It displays the total amount of free and used physical and swap memory in the system, as well as the buffers and caches used by the kernel. The information is gathered by parsing /proc/meminfo.
- total - Total installed memory (MemTotal and SwapTotal in /proc/meminfo)
- used - Used memory (calculated as total - free - buffers - cache)
- free - Unused memory (MemFree and SwapFree in /proc/meminfo)
- shared - Memory used (mostly) by tmpfs (Shmem in /proc/meminfo, available on kernels 2.6.32, displayed as zero if not available)
- buffers - Memory used by kernel buffers (Buffers in /proc/meminfo. "Buffers" represent how much portion of RAM is dedicated to cache disk blocks.
- cache - Memory used by the page cache and slabs (Cached and SReclaimable in /proc/meminfo). "Cached" is similar like "Buffers", only this time it caches pages from file reading.
- buff/cache - Sum of buffers and cache
- available - Estimation of how much memory is available for starting new applications, without swapping.
- Unlike the data provided by the cache or free fields, this field takes into account page cache and also that not all reclaimable memory slabs will be reclaimed due to items being in use (MemAvailable in /proc/meminfo, available on kernels 3.14, emulated on kernels 2.6.27+, otherwise the same as free)
How to use free
Some common ‘free’ command options:
-b,-k,-m,-g show output in bytes, KB, MB, or GB
-l show detailed low and high memory statistics
-t display total for RAM + swap
-s update every [delay] seconds
-c update [count] times
Examples:
$ free
total used free shared buff/cache available
Mem: 984180 494120 240972 716 249088 349920
Swap: 0 0 0
$ free -h
total used free shared buff/cache available
Mem: 961M 482M 235M 716K 243M 341M
Swap: 0B 0B 0B
$ free -m
total used free shared buff/cache available
Mem: 961 483 234 0 243 340
Swap: 0 0 0
$ free -k
total used free shared buff/cache available
Mem: 984180 493416 241592 716 249172 350624
Swap: 0 0 0
# Display a line containing the total memory in MB
$ free -t -h
total used free shared buff/cache available
Mem: 961M 479M 237M 716K 243M 344M
Swap: 0B 0B 0B
Total: 961M 479M 237M
/proc/meminfo
/proc/meminfo stores statistics about memory usage on the Linux system. The same file is used by free and other utilities to report the amount of free and used memory (physical and swap) on the system, as well as the shared memory and buffers used by the kernel.
$ less /proc/meminfo $ more /proc/meminfo $ egrep --color 'Mem|Cache|Swap' /proc/meminfo
$ cat /proc/meminfo MemTotal: 984180 kB MemFree: 248040 kB MemAvailable: 357272 kB Buffers: 0 kB Cached: 214256 kB SwapCached: 0 kB Active: 485564 kB Inactive: 128240 kB Active(anon): 394264 kB Inactive(anon): 376 kB Active(file): 91300 kB Inactive(file): 127864 kB Unevictable: 0 kB Mlocked: 0 kB SwapTotal: 0 kB SwapFree: 0 kB Dirty: 0 kB . . . . [Long output]
$ egrep --color 'Mem|Cache|Swap' /proc/meminfo MemTotal: 984180 kB MemFree: 248396 kB MemAvailable: 357836 kB Cached: 214464 kB SwapCached: 0 kB SwapTotal: 0 kB SwapFree: 0 kB
References: