Process Control Tools
Process Control Tools
Copyright(c) Management Analytics, 1995 - All Rights Reserved
Copyright(c), 1990, 1995 Dr. Frederick B. Cohen - All Rights Reserved
- The Login program identifies and authenticates a
user, and creates a process for that user by
running a system specified program. The terminal being used by the
user for login is normally attached to that process
for input and output, and the default program run at login is
normally the Sh command interpreter.
- The Sh program is designed as an interactive interface
between the user and the operating system (commonly called a
``command interpreter''). This program allows the user to specify
programs, ``command line'' arguments, inputs to those programs, and
output from those programs. It then takes the specifications and
translates them into appropriate sequences of system calls. Sh
also has a substantial programming capability and can interpret commands
from files, thus making is a powerful language for performing
many of the tasks that would require programs in other operating
environments.
- The Csh program is a version of the Sh program that
provides a command syntax similar to the ``C'' language.
- The Ps program produces a list of processes on the
system and their status. Depending on the command line parameters
passed to Ps, it can list processes from the current
user or all users, and list various subsets of the
available information on those processes. The available
information includes the Pid, Gid, parent, system
time, user time, IO time, name of the calling program and command
line parameters, and process scheduler status.
- The Newgrp program changes the group of the current
process.
- The Kill program sends a specified signal to a specified
process or set of processes. It is most commonly used to
terminate a process, but is occasionally used to send other
signals.
- The At program schedules a process for a later time
and date. This is most often used to perform ``batch'' processing,
schedule processing for the evening hours, or (on occasion) to do
something at a particular date and time in the future. The Cron
program facility is normally used for periodic tasks.
- The Cron program is a program that chronically wakes up to
run programs scheduled for particular times and dates. Cron can
be used to schedule specific events, but more often is used for periodic
processing like remote mail delivery and reminding the operator to do
backups.
- The Nice program requests that the system scheduler change
the priority with which the present and all subprocesses be
scheduled to run. For normal users, Nice can only lower
the execution priority, but for the superuser, Nice can be
used to schedule higher priorities as well. Priorities on most
UNIX systems range from -127 to 128, with -127 being the
``highest'' priority. User programs normally run at priority 0,
while device drivers tend to run at negative priorities, with DMA
priorities more negative then sequential devices.
- The Time program times a subprocess, returning the
User CPU time, system CPU time, and real time.