IBM REDP-4285-00 User Manual

Chapter 2. Monitoring and benchmark tools

Draft Document for Review May 4, 2007 11:35 am

4285ch02.fm

Figure 2-1 free command output

Useful parameters for the free command include:

-b, -k, -m, -g

display values in bytes, kilobytes, megabytes, and gigabytes.

-l

distinguishes between low and high memory (refer to 1.2, “Linux memory
architecture” on page 11).

-c <count>

displays the free output <count> number of times.

Memory used in a zone

Using the -l option, you can see how much memory is used in each memory zone.
Example 2-8 and Example 2-9 show the example of free -l output of 32 bit and 64 bit
system. Notice that 64-bit system no longer use High memory.

Example 2-8 Example output from the free command on 32 bit version kernel

[root@edam ~]# free -l
          total       used       free     shared   buffers     cached
Mem:       4154484    2381500   1772984         0    108256    1974344
Low:        877828    199436     678392
High:      3276656    2182064   1094592
-/+ buffers/cache:    298900   3855584
Swap:      4194296          0   4194296

Example 2-9 Example output from the free command on 64 bit version kernel

[root@lnxsu4 ~]# free -l
          total       used       free     shared   buffers     cached
Mem:       4037420    138508   3898912         0    10300     42060
Low:       4037420    138508   3898912
High:          0         0        0
-/+ buffers/cache:      86148   3951272

#free -m

total used free shared buffers cached

Mem: 4092 3270 826 0

36 1482

-/+ buffers/cache: 1748 2344
Swap: 4096 0 4096

free
memory
(KB)

used
memory
(KB)

shared
memory
(KB)

buffer
(KB)

cache
(KB)

Free= 826(MB)

Buffer=36(MB)

Cache=1482(MB)

Used=1748(MB)

memory 4GB

Free= 826(MB)

Buffer=36(MB)

Cache=1482(MB)

Used=1748(MB)

memory 4GB

total amount
of memory
(KB)

Mem

: used = Used + Buffer + Cache / free = Free

-/+ buffers/cache

: used = Used / free = Free + Buffer + Cache