free

What it does

free -h prints total, used and free memory, the shared memory, the buffers and cache, and available: the memory programs can still get (free + cache the kernel can give back). Look at "available", not "free" — Linux uses spare RAM as cache on purpose.

How to write it

free [OPTION]...

Options 17

Most used

-h, --human: Readable units (Mi, Gi).
-b, --bytes: In bytes.
-k, --kibi: In KiB (default).
-m, --mebi: In MiB.
-g, --gibi: In GiB.
--tebi, --pebi: In TiB or PiB.
--kilo, --mega, --giga, --tera, --peta: Powers of 1000 (implies --si).
--si: Use 1000 instead of 1024.
-w, --wide: Buffers and cache in their own columns.
-t, --total: Add a total line (RAM + swap).
-l, --lohi: Low and high memory details.
-L, --line: Everything on one line.
-v, --committed: Show committed memory.
-s, --seconds DELAY: Repeat every DELAY seconds.
-c, --count COUNT: Repeat COUNT times.
--help: Show help.
-V, --version: Show the version.

Examples 10

$ run as a normal user# run as root (or with sudo)

1Memory in readable units

$free -h
               total        used        free      shared  buff/cache   available
Mem:           3.6Gi       812Mi       2.1Gi        12Mi       891Mi       2.6Gi
Swap:          4.0Gi          0B       4.0Gi

available = what new programs can still use.

2Wide view
```
$free -hw
```
Buffers and cache apart.
3Watch every 2 seconds
```
$free -h -s 2
```
Ctrl+C to stop.
4With a total line
```
$free -ht
```
RAM + swap together.

5Value for a script

$free -m | awk '/^Mem:/ {print $7}'
2662

Available MiB.

6One line
```
$free -hL
```
Short for logs.
7Is swap used a lot?
```
$free -h | grep Swap; vmstat 1 5
```
High si/so in vmstat = the system swaps actively (too little RAM).
8Drop the cache for a test (not in production)
```
#sync; echo 3 > /proc/sys/vm/drop_caches; free -h
```
Shows that cache is given back.
9Who uses the memory?
```
$ps -eo pid,rss,cmd --sort=-rss | head
```
free shows totals; ps shows the processes.
10Check OOM killer events (security/stability)
```
#journalctl -k | grep -i 'out of memory'
```
The kernel killed a process because memory was full.

Files

/proc/meminfo: The source of the numbers.

Exit codes

0 :: Done. 1 :: Error.

`free`

What it does

How to write it

Options 17

Examples 10

1Memory in readable units

2Wide view

3Watch every 2 seconds

4With a total line

5Value for a script

6One line

7Is swap used a lot?

8Drop the cache for a test (not in production)

9Who uses the memory?

10Check OOM killer events (security/stability)

Files

Exit codes

Full manual

What it does

How to write it

Options 17

Examples 10

1Memory in readable units

2Wide view

3Watch every 2 seconds

4With a total line

5Value for a script

6One line

7Is swap used a lot?

8Drop the cache for a test (not in production)

9Who uses the memory?

10Check OOM killer events (security/stability)

Files

Exit codes

Related commands

Used in these lessons

Full manual

`free`