Formula for used% in linux
free -o
total used free shared buffers cached
Mem: 8167004 8115292 51712 0 87680 1444676
Swap: 8388584 3252996 5135588
((memUsed-mebBuffers-memCached)*100)/memTotal => totalMemoryUsed%
((8115292-87680-1444676)*100/8167004) => 81%
Display free memory in Linux / Ubuntu
Short Answer:
free -m | awk 'NR==3 {print $4 " MB"}'
The command 'free' displays some formatted information from /proc/meminfo.
The throw '-m' displays these numbers in rounded megabytes.
# free -m
total used free shared buffers cached
Mem: 4049 3982 67 0 16 3530
-/+ buffers/cache: 435 3614
Swap: 6142 53 6088
It's strange, cause I always figured the "first row, third column" - right under 'FREE' - would be the amount of free memory on a Linux system. But that number was always low after I'd been running awhile.
And it turns out that it is NOT really what I was looking for. A more accurate representation of the memory being used by your applications and available for new processes is displayed in the SECOND line.
In addition to the memory that is actually being USED by the kernel and processes resident in memory - Linux also reserves memory to allocate to processes as 'buffers' AND uses pretty much any left over memory to hold "cached" files.
Looking only at the top line...
total = all memory in the system (4GB on this server)
used = all memory currently in use/reserved by running processes and the OS
free = total - used
shared = memory being shared by multiple processes (deprecated?)
buffers = memory reserved by the OS to alloc as buffers when process need them (aka the 'heap')
cached = recently used files being stored in ram (THANK YOU LINUX!)
Here's a simple example I found to show off the power of 'caching':
for i in 1 2 ; do free -o; time grep -r foo /usr/bin >/dev/null 2>/dev/null; done
So really the buffers would be allocated to a running process if it asked for them anyway, and the memory being used to cache copies of recently used files would be released immediately if it makes sense to allocate the RAM elsewhere. So all that memory is 'available'.
Using these definitions:
When thinking about 'how much memory is really being used' - I want to calculate:
'used' - ('buffers' + 'cached')
When thinking about 'how much memory is really free' - I want to calculate:
'free' + ('buffers' + 'cached')
With this in mind, the meaning of the second row header form the output of the Linux command "free" (-/+ buffers/cache:) makes more sense...
Free is doing some light lifting for us, using the formula's above to display:
"minus buffers and cache" for the used column
and
"plus buffers and cache" for the free colum
So when you run free on Linux - the amount of free memory is always displayed right there in the second row, third column. Hence the 'Short Answer'...
Short Answer:
free -m | awk 'NR==3 {print $4 " MB"}'
The command 'free' displays some formatted information from /proc/meminfo.
The throw '-m' displays these numbers in rounded megabytes.
# free -m
total used free shared buffers cached
Mem: 4049 3982 67 0 16 3530
-/+ buffers/cache: 435 3614
Swap: 6142 53 6088
It's strange, cause I always figured the "first row, third column" - right under 'FREE' - would be the amount of free memory on a Linux system. But that number was always low after I'd been running awhile.
And it turns out that it is NOT really what I was looking for. A more accurate representation of the memory being used by your applications and available for new processes is displayed in the SECOND line.
In addition to the memory that is actually being USED by the kernel and processes resident in memory - Linux also reserves memory to allocate to processes as 'buffers' AND uses pretty much any left over memory to hold "cached" files.
Looking only at the top line...
total = all memory in the system (4GB on this server)
used = all memory currently in use/reserved by running processes and the OS
free = total - used
shared = memory being shared by multiple processes (deprecated?)
buffers = memory reserved by the OS to alloc as buffers when process need them (aka the 'heap')
cached = recently used files being stored in ram (THANK YOU LINUX!)
Here's a simple example I found to show off the power of 'caching':
for i in 1 2 ; do free -o; time grep -r foo /usr/bin >/dev/null 2>/dev/null; done
So really the buffers would be allocated to a running process if it asked for them anyway, and the memory being used to cache copies of recently used files would be released immediately if it makes sense to allocate the RAM elsewhere. So all that memory is 'available'.
Using these definitions:
When thinking about 'how much memory is really being used' - I want to calculate:
'used' - ('buffers' + 'cached')
When thinking about 'how much memory is really free' - I want to calculate:
'free' + ('buffers' + 'cached')
With this in mind, the meaning of the second row header form the output of the Linux command "free" (-/+ buffers/cache:) makes more sense...
Free is doing some light lifting for us, using the formula's above to display:
"minus buffers and cache" for the used column
and
"plus buffers and cache" for the free colum
So when you run free on Linux - the amount of free memory is always displayed right there in the second row, third column. Hence the 'Short Answer'...
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