A simple terminal locking application for Linux. Compile with: gcc -o tlock tlock.c -lpam -lpam_misc

tlock.c

#include <security/pam_appl.h>
#include <security/pam_misc.h>
#include <signal.h>
#include <stdio.h>
#include <string.h>
#include <time.h>

/**
 * Code adapted from:
 * PAM: http://www.makelinux.net/alp/084
 * Screen clearing: http://stackoverflow.com/a/263650/907773
 * Signal handling: http://www.yolinux.com/TUTORIALS/C++Signals.html
 * Time display: http://www.cplusplus.com/reference/ctime/strftime/
 */

pam_handle_t *pamh;
struct pam_conv pamc;
char timeBuffer[80];
char message[100];
short useMessage = 0;

void lockTerm();
void signalHandler(int sig);

int main(int argc, char* argv[]) {
	time_t rawtime;
	struct tm * timeinfo;
	time (&rawtime);
	timeinfo = localtime(&rawtime);
	strftime(timeBuffer, 80, "%T on %a %F", timeinfo);
	int i = 0;
	for(i = 1; i < argc - 1; i++) {
		if (strcmp(argv[i], "-m")==0) {
			strcpy(message, argv[++i]);
			useMessage = 1;
		}
	}
	signal(SIGHUP, signalHandler);
	signal(SIGINT, signalHandler);
	signal(SIGQUIT, signalHandler);
	signal(SIGTERM, signalHandler);
	signal(SIGTSTP, signalHandler);
	pamc.conv = &misc_conv;
	pamc.appdata_ptr = NULL;
	pam_start("common-auth", getenv("USER"), &pamc, &pamh);
	lockTerm();
	pam_end(pamh, 0);
	return 0;
}

void lockTerm() {
	write(1,"\E[H\E[2J",7);
	fprintf(stderr, "Terminal locked since %s by %s.\n", timeBuffer, getenv("USER"));
	if (useMessage == 1) fprintf(stderr, "Message: %s\n", message);
	while (pam_authenticate(pamh, 0) != PAM_SUCCESS) {
		fprintf(stderr, "Authentication failed.\n");
	}
	fprintf(stderr, "Terminal unlocked.\n");
}

void signalHandler(int sig) {
	write(1,"\E[H\E[2J",7);
	fprintf(stderr, "Terminal locked since %s by %s.\n", timeBuffer, getenv("USER"));
}