92 lines
2.2 KiB
C
92 lines
2.2 KiB
C
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/* This file is part of the sample code and exercises
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* used by the class "Advanced Programming in the UNIX
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* Environment" taught by Jan Schaumann
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* <jschauma@netmeister.org> at Stevens Institute of
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* Technology.
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*
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* This file is in the public domain.
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*
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* You don't have to, but if you feel like
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* acknowledging where you got this code, you may
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* reference me by name, email address, or point
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* people to the course website:
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* https://stevens.netmeister.org/631/
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*/
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/* This program illustrates the use of getpriority(2)
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* and setpriority(2). It shows that we can adjust
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* our priority by lowering it, but that we can't
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* raise it again afterwards, unless we are root.
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*
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* Run as
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* $ ./a.out 5
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* $ sudo ./a.out 5
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* $ nice -n 10 ./a.out 5
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* $ nice -n 10 ./a.out 15
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* $ nice -n -5 ./a.out 5
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*/
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#include <sys/resource.h>
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#include <err.h>
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#include <errno.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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int
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main(int argc, char **argv) {
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int n, p1, p2;
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if (argc != 2) {
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fprintf(stderr, "Usage: %s num\n", argv[0]);
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exit(EXIT_FAILURE);
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}
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/* If argv[1] is not a valid number, then we
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* get 0, but so be it, we'll use that. */
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n = atoi(argv[1]);
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errno = 0;
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if ((p1 = getpriority(PRIO_PROCESS, getpid())) == -1) {
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if (errno != 0) {
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err(EXIT_FAILURE, "getpriority");
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/* NOTREACHED */
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}
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}
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(void)printf("My current priority is: %d\n", p1);
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if (setpriority(PRIO_PROCESS, getpid(), n) == -1) {
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err(EXIT_FAILURE, "setpriority");
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/* NOTREACHED */
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}
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errno = 0;
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if ((p2 = getpriority(PRIO_PROCESS, getpid())) == -1) {
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if (errno != 0) {
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err(EXIT_FAILURE, "getpriority");
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/* NOTREACHED */
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}
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}
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(void)printf("My new priority is: %d\n", p2);
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/* We expect this to fail when running with
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* euid != 0, since we can't raise our
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* priority even to a value we initially had.
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*/
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if (setpriority(PRIO_PROCESS, getpid(), p1) == -1) {
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(void)fprintf(stderr, "Unable to setpriority(): %s\n", strerror(errno));
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}
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errno = 0;
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if ((p2 = getpriority(PRIO_PROCESS, getpid())) == -1) {
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if (errno != 0) {
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err(EXIT_FAILURE, "getpriority");
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/* NOTREACHED */
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}
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}
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(void)printf("My priority %sis: %d\n", (p1 != p2) ? "still " : "", p2);
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return 0;
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}
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