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free

The free command in Unix and Linux systems is used to display information about the system's memory usage, including total and used memory, free memory, swap usage, and buffer/cache usage.

Basic Usage

Simply type free in your terminal:

free

Output Format

The free command typically outputs information in the following format:

              total        used        free      shared  buff/cache   available
Mem:        1635412      467908      587084       44644      580420      922572
Swap:       2097148      192224     1904924
  • total: Total amount of physical memory (RAM) in kilobytes.
  • used: Used memory, in kilobytes.
  • free: Free memory, in kilobytes.
  • shared: Memory used (shared by processes), in kilobytes.
  • buff/cache: Memory used as buffers/cache, in kilobytes.
  • available: Estimate of how much memory is available for starting new applications, in kilobytes.

For swap:

  • Swap: Total amount of swap memory (if available).
  • used: Used swap memory.
  • free: Free swap memory.

Practical Use Cases

  • Monitoring Memory Usage: Quickly check how much memory is being used and how much is free.
  • Identifying Memory Pressure: Determine if the system is running low on available memory.
  • Checking Swap Usage: Assess whether swap space is being utilized and if there might be performance implications.

Summary

The free command provides essential information about system memory usage, including both physical memory (RAM) and swap space. It's a useful tool for monitoring system resources, diagnosing performance issues related to memory, and understanding the overall health of the system on Unix and Linux platforms.

help

Usage:
 free [options]

Options:
 -b, --bytes         show output in bytes
     --kilo          show output in kilobytes
     --mega          show output in megabytes
     --giga          show output in gigabytes
     --tera          show output in terabytes
     --peta          show output in petabytes
 -k, --kibi          show output in kibibytes
 -m, --mebi          show output in mebibytes
 -g, --gibi          show output in gibibytes
     --tebi          show output in tebibytes
     --pebi          show output in pebibytes
 -h, --human         show human-readable output
     --si            use powers of 1000 not 1024
 -l, --lohi          show detailed low and high memory statistics
 -t, --total         show total for RAM + swap
 -s N, --seconds N   repeat printing every N seconds
 -c N, --count N     repeat printing N times, then exit
 -w, --wide          wide output

     --help     display this help and exit
 -V, --version  output version information and exit

For more details see free(1).