On Tue, 31 Oct 2000, Carel Fellinger wrote:
>down /etc/init.d/eam tcp nowait carel /usr/bin/ssh /usr/bin/ssh iae
bin/nc mail.iae.nl eam tcp nowait carel /usr/bin/ssh /usr/bin/ssh ire
bin/nc uucp.iae.nl uucp-pipes stop
Come again?
> > SSHARGS="${SSHFLAGS} -l ${USER} -L ${LOCALPORT}:${DEST}:${REMOTEPORT}
> > ${HOST} ${PIPE}l"
>
> what is this ${PIPE}l? some program you run on the other side?
> I would have expected something like "sleep forever".
Oh yeah. It's basically "sleep forever" except replace "sleep" with
"wait" and add this feature: if an instance of the program already
exists, replace it with this one. Code follows below.
> So I did it differently using tcp-wrappers/inetd, like this:
Cool, let me try it..
-chris
/* program that hangs forever */
/* only one instance of it (by a given name) may run at a time */
/* ln(1) the executable to whatever names you need */
#include <stdio.h>
#include <unistd.h>
#include <strings.h>
#include <sys/types.h>
#include <signal.h>
#include <stdlib.h>
#include <malloc.h>
#include <libgen.h>
int
main(int arc, const char** argv)
{
const char* home = getenv("HOME");
char* fullName = (char *)malloc(1000*sizeof(char));
char* name = NULL;
pid_t pid = getpid();
pid_t previousPid = 0;
char* fileName = (char*)malloc(1000*sizeof(char));
FILE* file = NULL;
int _signal = 9;
strcpy(fullName, argv[0]);
name = basename(fullName);
fileName[0] = (char)0;
strcat(fileName, home);
strcat(fileName, "/var/run/");
strcat(fileName, name);
strcat(fileName, ".pid");
file = fopen(fileName, "r");
if (file == NULL) {
fprintf(stderr, "Failed to open file '%s' for reading\n", fileName);
exit(1);
}
fscanf(file, "%d", &previousPid);
if (previousPid != pid) {
if (previousPid > 0) {
/* There is a race condition here. If we kill the old instance
before overwriting its PID, a third instance could try to kill
a nonexistent process. If on the other hand we overwrite
the PID first, a third instance could kill us before we have
a chance to kill the old instance.
*/
int result = kill(previousPid, _signal);
if (result != 0) {
fprintf(stderr,
"Failed to kill PID '%d' with signal '%d'\n"
"Continuing anyway...\n",
previousPid,
_signal);
}
}
} else {
fprintf(stderr,
"Suicide attempt thwarted\n");
exit(1);
}
{
int result;
fclose(file);
file = fopen(fileName, "w");
if (file == NULL) {
fprintf(stderr, "Failed to open file '%s' for writing\n", fileName);
exit(1);
}
fprintf(file, "%d", pid);
fflush(file);
fclose(file);
result = pause();
fprintf(stderr, "pause() returned value '%d'\n", result);
return 0;
}
}
