Memory

RAM

Linux Memory Types

1. physical memory - resource containing code and data.
2. swap file - optional. Keeps (dirty) modified memory for later use if too many demands are made on physical memory.
3. virtual memory - "unlimited" (...)

No matter the memory type - all are managed as pages (typically 4096 bytes)

Memory monitoring tools

1. free (-m to show in MB)

Header	Description
total	indicates memory/physical RAM available for your machine. By default these numbers are in KB's
used	indicates memory/RAM used by system. This includes buffers and cached data size as well
free	indicates total unused RAM available for new process to run
shared	indicates shared memory. This column is obsolete and may be removed in future releases of free
buffers	indicates total RAM buffered by different applications in Linux
cached	indicates total RAM used for Caching of data for future purpose
-/+ buffers/cache	shows used column minus (buffers+cached) and free column plus (buffers+cached). Why is that? Because when memory used is getting up to limit, the buffers + cache will be freed and used by demanding applications. This show most accurate memory usage.
New version of free:

• buff/cache: sum of buffers and cached
• available: not exactly free column plus (buffers+cached)

2. top

Header	Description
virt
res
shr
%mem