If you want to kill a process and you don't care about being nice, this is the signal you want. For scripts and other programs with no signal handler, however, it not only kills the running script but it also kills the shell session in which the script is running this may not be the behavior that you want.
The program's signal handler must intercept incoming signals and act accordingly. It may also be the least effective because the program must have a signal handler built into it. SIGTERM (15): Signal 15, SIGTERM is the default signal sent by top and the other monitors when the k key is pressed.Three of these signals can be used to kill a process. The kill -l can be used to list all possible signals that can be sent. The separate kill command can also be used to send signals to processes outside of the monitors. Each of these signals has a specific function though some of them can be defined by the receiving program using signal handlers. SignalsĪll of the monitors discussed here allow you to send signals to running processes.
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Linux Journal has an excellent article describing load averages, the theory and the math behind them, and how to interpret them in the Decemissue. The longer-term load averages provide indication of the overall utilization trend. That would mean that every CPU is fully utilized and yet no instruction must be forced to wait. The optimum condition for load average is for it to equal the total number of CPUs in a system. A perfectly utilized 4 CPU system would show a load average of 4.00 so that the system in the example is fully loaded but not overloaded. In the example above, a 4 CPU system has a 1 minute load average of 4.04 meaning that there is no remaining capacity among the 4 CPUs and a few instructions are forced to wait. If it has a load average of 3.24, for example, then three of its processors are fully utilized and one is utilized at about 76%. If a 4 CPU system has a load average of 4 then it has perfect utilization. This is also true for multiple processors. For example, a load average of 1.5 in a single CPU system indicates that one-third of the CPU instructions are forced to wait to be executed until the one preceding it has completed. A load average of less than one means that the CPU is underutilized and a load average of greater than 1 means that the CPU is overutilized and that there is pent-up, unsatisfied demand.
This means that the CPU is keeping up exactly with the demand in other words it has perfect utilization. So this is a true measure of CPU performance, unlike the standard "CPU percentage" which includes I/O wait times during which the CPU is not really working.įor example, a fully utilized single processor system CPU would have a load average of 1. Load averages are an important criteria for measuring CPU usage, but what does this really mean when I say that the 1 (or 5 or 10) minute load average is 4.04, for example? Load average can be considered a measure of demand for the CPU it is a number that represents the average number of instructions waiting for CPU time. Load averagesīefore I go on to discuss the monitoring tools, it is important to discuss load averages in more detail. All provide near real-time views of system activity. Some monitor other aspects of a Linux system as well. For me, these are top, atop, htop, and glances.Īll of these tools monitor CPU and memory usage, and most of them list information about running processes at the very least. My go to tools for problem determination in a Linux environment are almost always the system monitoring tools. If I did not cover your favorite tool, please forgive me and let us all know what tools you use and why in the comments section. This article concentrates on the tools that I typically use.
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