Linux Command Library


Display amount of free and used memory in the system

- Display system memory:

- Display memory in Bytes/KB/MB/GB:
free -[b|k|m|g]

- Display memory in human readable units:
free -h

- Refresh the output every 2 seconds:
free -s [2]

free [options]

free 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. The displayed columns are:

Total installed memory (MemTotal and SwapTotal in /proc/meminfo)
Used memory (calculated as total - free - buffers - cache)
Unused memory (MemFree and SwapFree in /proc/meminfo)
Memory used (mostly) by tmpfs (Shmem in /proc/meminfo)
Memory used by kernel buffers (Buffers in /proc/meminfo)
Memory used by the page cache and slabs (Cached and SReclaimable in /proc/meminfo)
Sum of buffers and cache
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)

-b, --bytes
Display the amount of memory in bytes.
-k, --kibi
Display the amount of memory in kibibytes. This is the default.
-m, --mebi
Display the amount of memory in mebibytes.
-g, --gibi
Display the amount of memory in gibibytes.
Display the amount of memory in tebibytes.
Display the amount of memory in pebibytes.
Display the amount of memory in kilobytes. Implies --si.
Display the amount of memory in megabytes. Implies --si.
Display the amount of memory in gigabytes. Implies --si.
Display the amount of memory in terabytes. Implies --si.
Display the amount of memory in petabytes. Implies --si.
-h, --human
Show all output fields automatically scaled to shortest three digit unit and display the units of print out. Following units are used.
 B = bytes K = kibibyte M = mebibyte G = gibibyte T = tebibyte P = pebibyte 

If unit is missing, and you have exbibyte of RAM or swap, the number is in tebibytes and columns might not be aligned with header.

-w, --wide
Switch to the wide mode. The wide mode produces lines longer than 80 characters. In this mode buffers and cache are reported in two separate columns.
-c, --count count
Display the result count times. Requires the -s option.
-l, --lohi
Show detailed low and high memory statistics.
-s, --seconds delay
Continuously display the result delay seconds apart. You may actually specify any floating point number for delay using either . or , for decimal point. usleep(3) is used for microsecond resolution delay times.
Use kilo, mega, giga etc (power of 1000) instead of kibi, mebi, gibi (power of 1024).
-t, --total
Display a line showing the column totals.
Print help.
-V, --version
Display version information.

memory information

The value for the shared column is not available from kernels before 2.6.32 and is displayed as zero.

Please send bug reports to

ps(1), slabtop(1), top(1), vmstat(8).

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