End      jump to end of input line

   Linux Memory Types
       For  our purposes there are three types of memory, and one is optional.  First is physical memory, a limited resource where code and data must reside when executed or referenced.  Next is the optional swap file, where
       modified (dirty) memory can be saved and later retrieved if too many demands are made on physical memory.  Lastly we have virtual memory, a nearly unlimited resource serving the following goals:

          1. abstraction, free from physical memory addresses/limits
          2. isolation, every process in a separate address space
          3. sharing, a single mapping can serve multiple needs
          4. flexibility, assign a virtual address to a file

       Regardless of which of these forms memory may take, all are managed as pages (typically 4096 bytes) but expressed by default in top as KiB (kibibyte).  The memory discussed under topic ‘2c. MEMORY  Usage’  deals  with
       physical memory and the swap file for the system as a whole.  The memory reviewed in topic ‘3. FIELDS / Columns Display’ embraces all three memory types, but for individual processes.

       For  each such process, every memory page is restricted to a single quadrant from the table below.  Both physical memory and virtual memory can include any of the four, while the swap file only includes #1 through #3.
       The memory in quadrant #4, when modified, acts as its own dedicated swap file.

                                     Private | Shared
                                 1           |          2
            Anonymous  . stack               |
                       . malloc()            |
                       . brk()/sbrk()        | . POSIX shm*
                       . mmap(PRIVATE, ANON) | . mmap(SHARED, ANON)
                      ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐+‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐
                       . mmap(PRIVATE, fd)   | . mmap(SHARED, fd)
          File‐backed  . pgms/shared libs    |
                                 3           |          4

       The following may help in interpreting process level memory values displayed as scalable columns and discussed under topic ‘3a. DESCRIPTIONS of Fields’.

          %MEM - simply RES divided by total physical memory
          CODE - the ‘pgms’ portion of quadrant 3
          DATA - the entire quadrant 1 portion of VIRT plus all
                 explicit mmap file‐backed pages of quadrant 3
          RES  - anything occupying physical memory which, beginning with
                 Linux‐4.5, is the sum of the following three fields:
                 RSan - quadrant 1 pages, which include any
                        former quadrant 3 pages if modified
                 RSfd - quadrant 3 and quadrant 4 pages
                 RSsh - quadrant 2 pages
          RSlk - subset of RES which cannot be swapped out (any quadrant)
          SHR  - subset of RES (excludes 1, includes all 2 & 4, some 3)
          SWAP - potentially any quadrant except 4
          USED - simply the sum of RES and SWAP
          VIRT - everything in‐use and/or reserved (all quadrants)

       Note: Even though program images and shared libraries are considered private to a process, they will be accounted for as shared (SHR) by the kernel.

1. COMMAND‐LINE Options
       Mandatory arguments to long options are mandatory for short options too.

       Although not required, the equals sign can be used with either option form and whitespace before and/or after the ‘=’ is permitted.

       -b, --batch
          Starts top in Batch mode, which could be useful for sending output from top to other programs or to a file.  In this mode, top will not accept input and runs until the iterations limit  you’ve  set  with  the  ‘-n’
          command-line option or until killed.

       -c, --cmdline-toggle
          Starts  top  with  the  last  remembered  ‘c’  state  reversed.   Thus,  if  top was displaying command lines, now that field will show