Chapter 12. Process Management

The process is the entity that the operating system uses to control the use of system resources. AIX Version 4 introduces the use of threads to control processor-time consumption, but most of the system management tools still require the administrator to refer to the process in which a thread is running, rather than to the thread itself.

See the System User's Guide: Operating System and Devices for basic information on managing your own processes; for example, restarting or stopping a process that you started or scheduling a process for a later time. The System User's Guide also defines terms that describe processes, such as daemons and zombies.

This chapter describes processes and the tools that the operating system provides to manage processes from the perspective of the system administrator rather than the general user.

AIX contains tools to:

• Observe the creation, cancellation, identity, and resource consumption of processes.
  • ps is used to report process IDs, users, CPU-time consumption, and other attributes.
  • who -u reports the shell process ID of logged-on users.
  • svmon is used to report process real-memory consumption. (See Performance Toolbox Version 1.2 and 2 for AIX: Guide and Reference for information on the svmon command.)
  • acct mechanism writes records at process termination summarizing the process's resource use. (See how to set up an accounting system in "Accounting Overview" .)
• Control the priority level at which a process contends for the CPU.
  • nice causes a command to be run with a specified process priority. (See AIX Version 4.3 System User's Guide: Operating System and Devices.)
  • renice changes the priority of a given process.
• Terminate processes that are out of control.
  • kill sends a termination signal to one or more processes.
• Tune the operating system's process-management mechanisms.
  • schedtune permits changes to the process scheduler parameters. (See AIX Versions 3.2 and 4 Performance Tuning Guide for information on the schedtune command.)

Process Monitoring

The ps command is the primary tool for observing the processes in the system. Most of the flags of the ps command fall into one of two categories:

• Flags that specify which types of processes to include in the output
• Flags that specify which attributes of those processes are to be displayed

The most widely useful variants of ps for system-management purposes are:

To identify the current heaviest users of CPU time, you could enter:

ps -ef | egrep -v "STIME|$LOGNAME" | sort +3 -r | head -n 15

This will list, in descending order, the 15 most CPU-intensive processes other than those owned by you.

For more specialized uses, the following two tables are intended to simplify the task of choosing ps flags by summarizing the effects of the flags.

If ps is given with no flags or with a process-specifying flag that begins with a minus sign, the columns displayed are those shown for Default1. If the command is given with a process-specifying flag that does not begin with minus, Default2 columns are displayed. The -u or -U flag is both a process-specifying and column-selecting flag.

The following are brief descriptions of the contents of the columns:

Process-Priority Alteration

For a detailed discussion of process-priority alteration, see "Controlling Contention for the CPU" in AIX Versions 3.2 and 4 Performance Tuning Guide. Basically, if you have identified a process that is using too much CPU time, you can reduce its effective priority by increasing its nice value with renice. For example:

renice +5 ProcID

The nice value of the ProcID's would increase process from the normal 20 of a foreground process to 25. To reset process ProcID's nice value to 20, you would have to be root and enter:

renice -5 ProcID

Process Termination

Use the kill command to end a process. The kill command sends a signal to the designated process. Depending on the type of signal and the nature of the program that is running in the process, the process may end or may keep running. The signals you would send are:

Normally, it is desirable to issue SIGTERM rather than SIGKILL. If the program has a handler for SIGTERM, it can clean up and terminate in an orderly fashion. You would issue:

kill -term ProcessID

(The -term could be omitted.) If the process does not respond to the SIGTERM, enter:

kill -kill ProcessID

Binding or Unbinding a Process

On multiprocessor systems, you can bind a process to a processor or unbind a previously bound process from:

• Web-based System Manager
• SMIT
• command line

  Note: While binding a process to a processor may lead to improved performance for the bound process (by decreasing hardware-cache misses), overuse of this facility could cause individual processors to become overloaded while other processors are underused. The resulting bottlenecks could reduce overall throughput and performance. During normal operations, it is better to let the operating system assign processes to processors automatically, distributing system load across all processors. Bind only those processes that you know will benefit from being run on a single processor.

Prerequisite

You must have root user authority to bind or unbind a process you do not own.