![]() ![]() The program provides a limited interactive interface for process manipulation as well as a much more extensive interface for personal configuration - encompassing every aspect of its operation. The types of system summary information shown and the types, order and size of information displayed for processes are all user configurable and that configuration can be made persistent across restarts. It can display system summary information as well as a list of processes or threads currently being managed by the Linux kernel. The top program provides a dynamic real-time view of a running system. Top – display Linux processes – uptime and load averages, task and cpu states and memory usage. Unlike the data provided by the cache or free fields, this field takes into account page cache and also that not all reclaimable memory slabs will be reclaimed due to items being in use (MemAvailable in /proc/meminfo, available on kernels 3.14, emulated on kernels 2.6.27+, otherwise the same as free) top ![]() Shared –Memory used (mostly) by tmpfs (Shmem in /proc/meminfo, available on kernels 2.6.32, displayed as zero if not available)īuffers – Memory used by kernel buffers (Buffers in /proc/meminfo)Ĭache – Memory used by the page cache and slabs (Cached and Slab in /proc/meminfo)Īvailable –Estimation of how much memory is available for starting new applications, without swapping. Used – Used memory (calculated as total – free – buffers – cache)įree – Unused memory (MemFree and SwapFree in /proc/meminfo) Total – Total installed memory (MemTotal and SwapTotal in /proc/meminfo) The information is gathered by parsing /proc/meminfo. free displays the total amount of free and used physical and swap memory in the system, as well as the buffers and caches used by the kernel. Paging is usually more efficient, and that's what Linux does, but traditional Linux terminology talks about swapping anyway.Free – Display amount of free and used memory in the system. ![]() This means that if you only occasionally need an unusual amount of swap space, you can set up an extra swap file at such times, instead of keeping the whole amount allocated all the time.Ī note on operating system terminology: computer science usually distinguishes between swapping (writing the whole process out to swap space) and paging (writing only fixed size parts, usually a few kilobytes, at a time). You should also know that Linux allows one to use several swap partitions and/or swap files at the same time. When you know how much swap space you need, you should go for a swap partition, but if you are uncertain, you can use a swap file first, use the system for a while so that you can get a feel for how much swap you need, and then make a swap partition when you're confident about its size. A swap partition is faster, but it is easier to change the size of a swap file (there's no need to repartition the whole hard disk, and possibly install everything from scratch). Linux can use either a normal file in the filesystem or a separate partition for swap space. The part of the hard disk that is used as virtual memory is called the swap space. Of course, reading and writing the hard disk is slower (on the order of a thousand times slower) than using real memory, so the programs don't run as fast. This is all made completely transparent to the user programs running under Linux only see the larger amount of memory available and don't notice that parts of them reside on the disk from time to time. When the original contents are needed again, they are read back into memory. The kernel will write the contents of a currently unused block of memory to the hard disk so that the memory can be used for another purpose. Linux supports virtual memory, that is, using a disk as an extension of RAM so that the effective size of usable memory grows correspondingly. Will be counted in VIRT and SHR, but only the parts of the libraryįile containing the functions being used will actually be loaded in Uses a few functions in a library, the whole library is mapped and In the case of libraries, it does not necessarily mean SHR indicates how much of the VIRT size is actually sharable (memory (This alsoĬorresponds directly to the %MEM column.) This will virtually alwaysīe less than the VIRT size, since most programs depend on the C Of how much actual physical memory a process is consuming. RES stands for the resident size, which is an accurate representation Program is able to access at the present moment. Have been mapped into it (most notably shared libraries), and memory Instance the video card’s RAM for the X server), files on disk that Memory it is actually using, memory it has mapped into itself (for VIRT stands for the virtual size of a process, which is the sum of I found this explanation from Mugurel Sumanariu very clear:
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