Memory Then we have the Mem line, representing
Memory Then we have the Mem line, representing actual physical RAM ({). Unlike Windows, which simply divides memory into “used” and “unused” categories, FreeBSD uses memory in several different ways. Active memory is the total amount of memory in use at the moment for running user programs and their data. When a program ends, the program information is put into inactive memory and the data pulled from the disk is put in the cache memory. Similarly, the Buf entry shows the size of the memory buffer. The memory buffer contains data recently called from disk. Free memory is unused. Wired memory is memory used for in-kernel data structures, as well as for particular system calls that must have a particular piece of memory immediately available. Wired memory is never swapped out. Swap Then we have the Swap line, (|), which simply represents the total swap available and how much is in use. Swapping is when the system uses the disk drive as additional memory. We’ll look at swap in more detail later in the chapter. Process List Finally, we have a list of the processes on the system and their basic characteristics (}). The table format is designed to present as much information as possible in as little space as possible. Every process is on its own line. Let’s look at each column in the following sections. PID First we have the process ID number, or PID. Every process running on the system has a unique PID. When you issue kill commands, you use the PID to identify the process you want to affect. Username Next is the username of the person running the process. If multiple processes consume large chunks of CPU or memory, and they are all owned by the same user ID, you know who to talk to. Priority and Nice The PRI (priority) and NICE columns are interrelated, and indicate how much precedence the system gives these processes. We’ll talk about priority and niceness a little later in the chapter. Size Size is the amount of memory that the system has set aside for this process. Resident Memory The RES column shows how much of the program is actually in memory, or resident, at the moment. A program might have a huge amount of memory reserved for it, but only be using a small fraction of it. State The STATE column shows what the process is doing at the moment. Processes can be in a variety of states at any given time: waiting for input, sleeping until something wakes them, actively running, and so on. 410
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